e
'\"	enclosed in one large box.
'\"
'\" .BE
'\"	End of box enclosure.
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'\" .CS
'\"	Begin code excerpt.
'\"
'\" .CE
'\"	End code excerpt.
'\"
'\" .VS ?version? ?br?
'\"	Begin vertical sidebar, for use in marking newly-changed parts
'\"	of man pages.  The first argument is ignored and used for recording
'\"	the version when the .VS was added, so that the sidebars can be
'\"	found and removed when they reach a certain age.  If another argument
'\"	is present, then a line break is forced before starting the sidebar.
'\"
'\" .VE
'\"	End of vertical sidebar.
'\"
'\" .DS
'\"	Begin an indented unfilled display.
'\"
'\" .DE
'\"	End of indented unfilled display.
'\"
'\" .SO
'\"	Start of list of standard options for a Tk widget.  The
'\"	options follow on successive lines, in four columns separated
'\"	by tabs.
'\"
'\" .SE
'\"	End of list of standard options for a Tk widget.
'\"
'\" .OP cmdName dbName dbClass
'\"	Start of description of a specific option.  cmdName gives the
'\"	option's name as specified in the class command, dbName gives
'\"	the option's name in the option database, and dbClass gives
'\"	the option's class in the option database.
'\"
'\" .UL arg1 arg2
'\"	Print arg1 underlined, then print arg2 normally.
'\"
'\" RCS: @(#) $Id: man.macros,v 1.4 2000/08/25 06:18:32 ericm Exp $
'\"
'\"	# Set up traps and other miscellaneous stuff for Tcl/Tk man pages.
.if t .wh -1.3i ^B
.nr ^l \n(.l
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.\}
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.SH "STANDARD OPTIONS"
.LP
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.LP
See the \\fBoptions\\fR manual entry for details on the standard options.
..
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.de OP
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Command-Line Name:	\\fB\\$1\\fR
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\\$1\l'|0\(ul'\\$2
..
.TH Tcl_Obj 3 8.1 Tcl "Tcl Library Procedures"
.BS
.SH NAME
Tcl_NewObj, Tcl_DuplicateObj, Tcl_IncrRefCount, Tcl_DecrRefCount, Tcl_IsShared, Tcl_InvalidateStringRep \- manipulate Tcl objects
.SH SYNOPSIS
.nf
\fB#include <tcl.h>\fR
.sp
Tcl_Obj *
\fBTcl_NewObj\fR()
.sp
Tcl_Obj *
\fBTcl_DuplicateObj\fR(\fIobjPtr\fR)
.sp
\fBTcl_IncrRefCount\fR(\fIobjPtr\fR)
.sp
\fBTcl_DecrRefCount\fR(\fIobjPtr\fR)
.sp
int
\fBTcl_IsShared\fR(\fIobjPtr\fR)
.sp
\fBTcl_InvalidateStringRep\fR(\fIobjPtr\fR)
.SH ARGUMENTS
.AS Tcl_Obj *objPtr in
.AP Tcl_Obj *objPtr in
Points to an object;
must have been the result of a previous call to \fBTcl_NewObj\fR.
.BE

.SH INTRODUCTION
.PP
This man page presents an overview of Tcl objects and how they are used.
It also describes generic procedures for managing Tcl objects.
These procedures are used to create and copy objects,
and increment and decrement the count of references (pointers) to objects.
The procedures are used in conjunction with ones
that operate on specific types of objects such as
\fBTcl_GetIntFromObj\fR and \fBTcl_ListObjAppendElement\fR.
The individual procedures are described along with the data structures
they manipulate.
.PP
Tcl's \fIdual-ported\fR objects provide a general-purpose mechanism
for storing and exchanging Tcl values.
They largely replace the use of strings in Tcl.
For example, they are used to store variable values,
command arguments, command results, and scripts.
Tcl objects behave like strings but also hold an internal representation
that can be manipulated more efficiently.
For example, a Tcl list is now represented as an object
that holds the list's string representation
as well as an array of pointers to the objects for each list element.
Dual-ported objects avoid most runtime type conversions.
They also improve the speed of many operations
since an appropriate representation is immediately available.
The compiler itself uses Tcl objects to
cache the instruction bytecodes resulting from compiling scripts.
.PP
The two representations are a cache of each other and are computed lazily.
That is, each representation is only computed when necessary,
it is computed from the other representation,
and, once computed, it is saved.
In addition, a change in one representation invalidates the other one.
As an example, a Tcl program doing integer calculations can
operate directly on a variable's internal machine integer
representation without having to constantly convert
between integers and strings.
Only when it needs a string representing the variable's value,
say to print it,
will the program regenerate the string representation from the integer.
Although objects contain an internal representation,
their semantics are defined in terms of strings:
an up-to-date string can always be obtained,
and any change to the object will be reflected in that string
when the object's string representation is fetched.
Because of this representation invalidation and regeneration,
it is dangerous for extension writers to access
\fBTcl_Obj\fR fields directly.
It is better to access Tcl_Obj information using
procedures like \fBTcl_GetStringFromObj\fR and \fBTcl_GetString\fR.
.PP
Objects are allocated on the heap
and are referenced using a pointer to their \fBTcl_Obj\fR structure.
Objects are shared as much as possible.
This significantly reduces storage requirements
because some objects such as long lists are very large.
Also, most Tcl values are only read and never modified.
This is especially true for procedure arguments,
which can be shared between the caller and the called procedure.
Assignment and argument binding is done by
simply assigning a pointer to the value. 
Reference counting is used to determine when it is safe to
reclaim an object's storage.
.PP
Tcl objects are typed.
An object's internal representation is controlled by its type.
Seven types are predefined in the Tcl core
including integer, double, list, and bytecode.
Extension writers can extend the set of types
by using the procedure \fBTcl_RegisterObjType\fR .

.SH "THE TCL_OBJ STRUCTURE"
.PP
Each Tcl object is represented by a \fBTcl_Obj\fR structure
which is defined as follows.
.CS
typedef struct Tcl_Obj {
	int \fIrefCount\fR;
	char *\fIbytes\fR;
	int \fIlength\fR;
	Tcl_ObjType *\fItypePtr\fR;
	union {
		long \fIlongValue\fR;
		double \fIdoubleValue\fR;
		VOID *\fIotherValuePtr\fR;
		struct {
			VOID *\fIptr1\fR;
			VOID *\fIptr2\fR;
		} \fItwoPtrValue\fR;
	} \fIinternalRep\fR;
} Tcl_Obj;
.CE
The \fIbytes\fR and the \fIlength\fR members together hold
.VS 8.1
an object's UTF-8 string representation,
which is a \fIcounted string\fR not containing null bytes (UTF-8 null
characters should be encoded as a two byte sequence: 192, 128.)
\fIbytes\fR points to the first byte of the string representation.
The \fIlength\fR member gives the number of bytes.
The byte array must always have a null byte after the last data byte,
at offset \fIlength\fR;
this allows string representations
to be treated as conventional null-terminated C strings.
.VE 8.1
C programs use \fBTcl_GetStringFromObj\fR and \fBTcl_GetString\fR to get
an object's string representation.
If \fIbytes\fR is NULL,
the string representation is invalid.
.PP
An object's type manages its internal representation.
The member \fItypePtr\fR points to the Tcl_ObjType structure
that describes the type.
If \fItypePtr\fR is NULL,
the internal representation is invalid.
.PP
The \fIinternalRep\fR union member holds
an object's internal representation.
This is either a (long) integer, a double-precision floating point number,
a pointer to a value containing additional information
needed by the object's type to represent the object,
or two arbitrary pointers.
.PP
The \fIrefCount\fR member is used to tell when it is safe to free
an object's storage.
It holds the count of active references to the object.
Maintaining the correct reference count is a key responsibility
of extension writers.
Reference counting is discussed below
in the section \fBSTORAGE MANAGEMENT OF OBJECTS\fR.
.PP
Although extension writers can directly access
the members of a Tcl_Obj structure,
it is much better to use the appropriate procedures and macros.
For example, extension writers should never
read or update \fIrefCount\fR directly;
they should use macros such as
\fBTcl_IncrRefCount\fR and \fBTcl_IsShared\fR instead.
.PP
A key property of Tcl objects is that they hold two representations.
An object typically starts out containing only a string representation:
it is untyped and has a NULL \fItypePtr\fR.
An object containing an empty string or a copy of a specified string
is created using \fBTcl_NewObj\fR or \fBTcl_NewStringObj\fR respectively.
An object's string value is gotten with
\fBTcl_GetStringFromObj\fR or \fBTcl_GetString\fR
and changed with \fBTcl_SetStringObj\fR.
If the object is later passed to a procedure like \fBTcl_GetIntFromObj\fR
that requires a specific internal representation,
the procedure will create one and set the object's \fItypePtr\fR.
The internal representation is computed from the string representation.
An object's e
eeeeeetwo representations are duals of each other:
changes made to one are reflected in the other.
For example, \fBTcl_ListObjReplace\fR will modify an object's
internal representation and the next call to \fBTcl_GetStringFromObj\fR
or \fBTcl_GetString\fR will reflect that change.
.PP
Representations are recomputed lazily for efficiency.
A change to one representation made by a procedure
such as \fBTcl_ListObjReplace\fR is not reflected immediately
in the other representation.
Instead, the other representation is marked invalid
so that it is only regenerated if it is needed later.
Most C programmers never have to be concerned with how this is done
and simply use procedures such as \fBTcl_GetBooleanFromObj\fR or
\fBTcl_ListObjIndex\fR.
Programmers that implement their own object types
must check for invalid representations
and mark representations invalid when necessary.
The procedure \fBTcl_InvalidateStringRep\fR is used
to mark an object's string representation invalid and to
free any storage associated with the old string representation.
.PP
Objects usually remain one type over their life,
but occasionally an object must be converted from one type to another.
For example, a C program might build up a string in an object
with repeated calls to \fBTcl_AppendToObj\fR,
and then call \fBTcl_ListObjIndex\fR to extract a list element from
the object.
The same object holding the same string value
can have several different internal representations
at different times.
Extension writers can also force an object to be converted from one type
to another using the \fBTcl_ConvertToType\fR procedure.
Only programmers that create new object types need to be concerned
about how this is done.
A procedure defined as part of the object type's implementation
creates a new internal representation for an object
and changes its \fItypePtr\fR.
See the man page for \fBTcl_RegisterObjType\fR
to see how to create a new object type.

.SH "EXAMPLE OF THE LIFETIME OF AN OBJECT"
.PP
As an example of the lifetime of an object,
consider the following sequence of commands:
.CS
\fBset x 123\fR
.CE
This assigns to \fIx\fR an untyped object whose
\fIbytes\fR member points to \fB123\fR and \fIlength\fR member contains 3.
The object's \fItypePtr\fR member is NULL.
.CS
\fBputs "x is $x"\fR
.CE
\fIx\fR's string representation is valid (since \fIbytes\fR is non-NULL)
and is fetched for the command.
.CS
\fBincr x\fR
.CE
The \fBincr\fR command first gets an integer from \fIx\fR's object
by calling \fBTcl_GetIntFromObj\fR.
This procedure checks whether the object is already an integer object.
Since it is not, it converts the object
by setting the object's \fIinternalRep.longValue\fR member
to the integer \fB123\fR
and setting the object's \fItypePtr\fR
to point to the integer Tcl_ObjType structure.
Both representations are now valid.
\fBincr\fR increments the object's integer internal representation
then invalidates its string representation
(by calling \fBTcl_InvalidateStringRep\fR)
since the string representation
no longer corresponds to the internal representation.
.CS
\fBputs "x is now $x"\fR
.CE
The string representation of \fIx\fR's object is needed
and is recomputed.
The string representation is now \fB124\fR.
and both representations are again valid.

.SH "STORAGE MANAGEMENT OF OBJECTS"
.PP
Tcl objects are allocated on the heap and are shared as much as possible
to reduce storage requirements.
Reference counting is used to determine when an object is
no longer needed and can safely be freed.
An object just created by \fBTcl_NewObj\fR or \fBTcl_NewStringObj\fR
has \fIrefCount\fR 0.
The macro \fBTcl_IncrRefCount\fR increments the reference count
when a new reference to the object is created.
The macro \fBTcl_DecrRefCount\fR decrements the count
when a reference is no longer needed and,
if the object's reference count drops to zero, frees its storage.
An object shared by different code or data structures has
\fIrefCount\fR greater than 1.
Incrementing an object's reference count ensures that
it won't be freed too early or have its value change accidently.
.PP
As an example, the bytecode interpreter shares argument objects
between calling and called Tcl procedures to avoid having to copy objects.
It assigns the call's argument objects to the procedure's
formal parameter variables.
In doing so, it calls \fBTcl_IncrRefCount\fR to increment
the reference count of each argument since there is now a new
reference to it from the formal parameter.
When the called procedure returns,
the interpreter calls \fBTcl_DecrRefCount\fR to decrement
each argument's reference count.
When an object's reference count drops less than or equal to zero,
\fBTcl_DecrRefCount\fR reclaims its storage.
Most command procedures do not have to be concerned about
reference counting since they use an object's value immediately
and don't retain a pointer to the object after they return.
However, if they do retain a pointer to an object in a data structure,
they must be careful to increment its reference count
since the retained pointer is a new reference.
.PP
Command procedures that directly modify objects
such as those for \fBlappend\fR and \fBlinsert\fR must be careful to
copy a shared object before changing it.
They must first check whether the object is shared
by calling \fBTcl_IsShared\fR.
If the object is shared they must copy the object
by using \fBTcl_DuplicateObj\fR;
this returns a new duplicate of the original object
that has \fIrefCount\fR 0.
If the object is not shared,
the command procedure "owns" the object and can safely modify it directly.
For example, the following code appears in the command procedure
that implements \fBlinsert\fR.
This procedure modifies the list object passed to it in \fIobjv[1]\fR
by inserting \fIobjc-3\fR new elements before \fIindex\fR.
.CS
listPtr = objv[1];
if (Tcl_IsShared(listPtr)) {
	listPtr = Tcl_DuplicateObj(listPtr);
}
result = Tcl_ListObjReplace(interp, listPtr, index, 0, (objc-3), &(objv[3]));
.CE
As another example, \fBincr\fR's command procedure
must check whether the variable's object is shared before
incrementing the integer in its internal representation.
If it is shared, it needs to duplicate the object
in order to avoid accidently changing values in other data structures.

.SH "SEE ALSO"
Tcl_ConvertToType, Tcl_GetIntFromObj, Tcl_ListObjAppendElement, Tcl_ListObjIndex, Tcl_ListObjReplace, Tcl_RegisterObjType

.SH KEYWORDS
internal representation, object, object creation, object type, reference counting, string representation, type conversion
'\"
'\" Copyright (c) 1989-1993 The Regents of the University of California.
'\" Copyright (c) 1994-1996 Sun Microsystems, Inc.
'\"
'\" See the file "license.terms" for information on usage and redistribution
'\" of this file, and for a DISCLAIMER OF ALL WARRANTIES.
'\" 
'\" RCS: @(#) $Id: Hash.3,v 1.10.2.1 2003/07/18 16:56:24 dgp Exp $
'\" 
'\" The definitions below are for supplemental macros used in Tcl/Tk
'\" manual entries.
'\"
'\" .AP type name in/out ?indent?
'\"	Start paragraph describing an argument to a library procedure.
'\"	type is type of argument (int, etc.), in/out is either "in", "out",
'\"	or "in/out" to describe whether procedure reads or modifies arg,
'\"	and indent is equivalent to second arg of .IP (shouldn't ever be
'\"	needed;  use .AS below instead)
'\"
'\" .AS ?type? ?name?
'\"	Give maximum sizes of arguments for setting tab stops.  Type and
'\"	name are examples of largest possible arguments that will be passed
'\"	to .AP later.  If args are omitted, default tab stops are used.
'\"
'\" .BS
'\"	Start box enclosure.  From here until next .BE, everything will be
'\"	enclosed in one large box.
'\"
'\" .BE
'\"	End of box enclosure.
'\"
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'\"	the version when the .VS was added, so that the sidebars can be
'\"	found and removed when they reach a certain age.  If another argument
'\"	is present, then a line break is forced before starting the sidebar.
'\"
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'\"	Start of description of a specific option.  cmdName gives the
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'\"	the option's class in the option database.
'\"
'\" .UL arg1 arg2
'\"	Print arg1 underlined, then print arg2 normally.
'\"
'\" RCS: @(#) $Id: man.macros,v 1.4 2000/08/25 06:18:32 ericm Exp $
'\"
'\"	# Set up traps and other miscellaneous stuff for Tcl/Tk man pages.
.if t .wh -1.3i ^B
.nr ^l \n(.l
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.de AP
.ie !"\\$4"" .TP \\$4
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.TH Tcl_Hash 3 "" Tcl "Tcl Library Procedures"
.BS
.SH NAME
Tcl_InitHashTable, Tcl_InitCustomHashTable, Tcl_InitObjHashTable, Tcl_DeleteHashTable, Tcl_CreateHashEntry, Tcl_DeleteHashEntry, Tcl_FindHashEntry, Tcl_GetHashValue, Tcl_SetHashValue, Tcl_GetHashKey, Tcl_FirstHashEntry, Tcl_NextHashEntry, Tcl_HashStats \- procedures to manage hash tables
.SH SYNOPSIS
.nf
\fB#include <tcl.h>\fR
.sp
\fBTcl_InitHashTable\fR(\fItablePtr, keyType\fR)
.sp
\fBTcl_InitCustomHashTable\fR(\fItablePtr, keyType, typePtr\fR)
.sp
\fBTcl_InitObjHashTable\fR(\fItablePtr\fR)
.sp
\fBTcl_DeleteHashTable\fR(\fItablePtr\fR)
.sp
Tcl_HashEntry *
\fBTcl_CreateHashEntry\fR(\fItablePtr, key, newPtr\fR)
.sp
\fBTcl_DeleteHashEntry\fR(\fIentryPtr\fR)
.sp
Tcl_HashEntry *
\fBTcl_FindHashEntry\fR(\fItablePtr, key\fR)
.sp
ClientData
\fBTcl_GetHashValue\fR(\fIentryPtr\fR)
.sp
\fBTcl_SetHashValue\fR(\fIentryPtr, value\fR)
.sp
char *
\fBTcl_GetHashKey\fR(\fItablePtr, entryPtr\fR)
.sp
Tcl_HashEntry *
\fBTcl_FirstHashEntry\fR(\fItablePtr, searchPtr\fR)
.sp
Tcl_HashEntry *
\fBTcl_NextHashEntry\fR(\fIsearchPtr\fR)
.sp
CONST char *
\fBTcl_HashStats\fR(\fItablePtr\fR)
.SH ARGUMENTS
.AS Tcl_HashSearch *searchPtr
.AP Tcl_HashTable *tablePtr in
Address of hash table structure (for all procedures but
\fBTcl_InitHashTable\fR, this must have been initialized by
previous call to \fBTcl_InitHashTable\fR).
.AP int keyType in
Kind of keys to use for new hash table.  Must be either
TCL_STRING_KEYS, TCL_ONE_WORD_KEYS, TCL_CUSTOM_TYPE_KEYS,
TCL_CUSTOM_PTR_KEYS, or an integer value greater than 1.
.AP Tcl_HashKeyType *typePtr in
Address of structure which defines the behaviour of the hash table.
.AP "CONST char" *key in
Key to use for probe into table.  Exact form depends on
\fIkeyType\fR used to create table.
.AP int *newPtr out
The word at \fI*newPtr\fR is set to 1 if a new entry was created
and 0 if there was already an entry for \fIkey\fR.
.AP Tcl_HashEntry *entryPtr in
Pointer to hash table entry.
.AP ClientData value in
New value to assign to hash table entry.  Need not have type
ClientData, but must fit in same space as ClientData.
.AP Tcl_HashSearch *searchPtr in
Pointer to record to use to keep track of progress in enumerating
all the entries in a hash table.
.BE
.SH DESCRIPTION
.PP
A hash table consists of zero or more entries, each consisting of a
key and a value.  Given the key for an entry, the hashing routines can
very quickly locate the entry, and hence its value. There may be at
most one entry in a hash table with a particular key, but many entries
may have the same value.  Keys can take one of four forms: strings,
one-word values, integer arrays, or custom keys defined by a
Tcl_HashKeyType structure (See section \fBTHE TCL_HASHKEYTYPE
STRUCTURE\fR below). All of the keys in a given table have the same
form, which is specified when the table is initialized.
.PP
The value of a hash table entry can be anything that fits in the same
space as a ``char *'' pointer.  Values for hash table entries are
managed entirely by clients, not by the hash module itself.  Typically
each entry's value is a pointer to a data structure managed by client
code.
.PP
Hash tables grow gracefully as the number of entries increases, so
that there are always less than three entries per hash bucket, on
average. This allows for fast lookups regardless of the number of
entries in a table.
.PP
The core provides three functions for the initialization of hash
tables, Tcl_InitHashTable, Tcl_InitObjHashTable and
Tcl_InitCustomHashTable.
.PP
\fBTcl_InitHashTable\fR initializes a structure that describes a new
hash table.  The space for the structure is provided by the caller,
not by the hash module.  The value of \fIkeyType\fR indicates what
kinds of keys will be used for all entries in the table. All of the
key types described later are allowed, with the exception of
\fBTCL_CUSTOM_TYPE_KEYS\fR and \fBTCL_CUSTOM_PTR_KEYS\fR.
.PP
\fBTcl_InitObjHashTable\fR is a wrapper around
\fBTcl_InitCustomHashTable\fR and initializes a hash table whose keys
are Tcl_Obj *.
.PP
\fBTcl_InitCustomHashTable\fR initializes a structure that describes a
new hash table. The space for the structure is provided by the
caller, not by the hash module.  The value of \fIkeyType\fR indicates
what kinds of keys will be used for all entries in the table.
\fIKeyType\fR must have one of the following values:
.IP \fBTCL_STRING_KEYS\fR 25
Keys are null-terminated strings.
They are passed to hashing routines using the address of the
first character of the string.
.IP \fBTCL_ONE_WORD_KEYS\fR 25
Keys are single-word values;  they are passed to hashing routines
and stored in hash table entries as ``char *'' values.
The pointer value is the key;  it need not (and usually doesn't)
actually point to a string.
.IP \fBTCL_CUSTOM_TYPE_KEYS\fR 25
Keys are of arbitrary type, and are stored in the entry. Hashing
and comparison is determined by \fItypePtr\fR. The Tcl_HashKeyType 
structure is described in the section 
\fBTHE TCL_HASHKEYTYPE STRUCTURE\fR below.
.IP \fBTCL_CUSTOM_PTR_KEYS\fR 25
Keys are pointers to an arbitrary type, and are stored in the entry. Hashing
and comparison is determined by \fItypePtr\fR. The Tcl_HashKeyType 
structure is described in the section 
\fBTHE TCL_HASHKEYTYPE STRUCTURE\fR below.
.IP \fIother\fR 25
If \fIkeyType\fR is not one of the above,
then it must be an integer value greater than 1.
In this case the keys will be arrays of ``int'' values, where
\fIkeyType\fR gives the number of ints in each key.
This allows structures to be used as keys.
All keys must have the same size.
Array keys are passed into hashing functions using the address
of the first int in the array.
.PP
\fBTcl_DeleteHashTable\fR deletes all of the entries in a hash
table and frees up the memory associated with the table's
bucket array and entries.
It does not free the actual table structure (pointed to
by \fItablePtr\fR), since that memory is assumed to be managed
by the client.
\fBTcl_DeleteHashTable\fR also does not free or otherwise
manipulate the values of the hash table entries.
If the entry values point to dynamically-allocated memory, then
it is the client's responsibility to free these structures
before deleting the table.
.PP
\fBTcl_CreateHashEntry\fR locates the entry corresponding to a
particular key, creating a new entry in the table if there
wasn't already one with the given key.
If an entry already existed with the given key then \fI*newPtr\fR
is set to zero.
If a new entry was created, then \fI*newPtr\fR is set to a non-zero
value and the value of the new entry will be set to zero.
The return value from \fBTcl_CreateHashEntry\fR is a pointer to
the entry, which may be used to retrieve and modify the entry's
value or to delete the entry from the table.
.PP
\fBTcl_DeleteHashEntry\fR will remove an existing entry from a
table.
The memory associated with the entry itself will be freed, but
the client is responsible for any cleanup associated with the
entry's value, such as freeing  e!e"e#e$e%ea structure that it points to.
.PP
\fBTcl_FindHashEntry\fR is similar to \fBTcl_CreateHashEntry\fR
except that it doesn't create a new entry if the key doesn't exist;
instead, it returns NULL as result.
.PP
\fBTcl_GetHashValue\fR and \fBTcl_SetHashValue\fR are used to
read and write an entry's value, respectively.
Values are stored and retrieved as type ``ClientData'', which is
large enough to hold a pointer value.  On almost all machines this is
large enough to hold an integer value too.
.PP
\fBTcl_GetHashKey\fR returns the key for a given hash table entry,
either as a pointer to a string, a one-word (``char *'') key, or
as a pointer to the first word of an array of integers, depending
on the \fIkeyType\fR used to create a hash table.
In all cases \fBTcl_GetHashKey\fR returns a result with type
``char *''.
When the key is a string or array, the result of \fBTcl_GetHashKey\fR
points to information in the table entry;  this information will
remain valid until the entry is deleted or its table is deleted.
.PP
\fBTcl_FirstHashEntry\fR and \fBTcl_NextHashEntry\fR may be used
to scan all of the entries in a hash table.
A structure of type ``Tcl_HashSearch'', provided by the client,
is used to keep track of progress through the table.
\fBTcl_FirstHashEntry\fR initializes the search record and
returns the first entry in the table (or NULL if the table is
empty).
Each subsequent call to \fBTcl_NextHashEntry\fR returns the
next entry in the table or
NULL if the end of the table has been reached.
A call to \fBTcl_FirstHashEntry\fR followed by calls to
\fBTcl_NextHashEntry\fR will return each of the entries in
the table exactly once, in an arbitrary order.
It is unadvisable to modify the structure of the table, e.g.
by creating or deleting entries, while the search is in
progress.
.PP
\fBTcl_HashStats\fR returns a dynamically-allocated string with
overall information about a hash table, such as the number of
entries it contains, the number of buckets in its hash array,
and the utilization of the buckets.
It is the caller's responsibility to free the result string
by passing it to \fBckfree\fR.
.PP
The header file \fBtcl.h\fR defines the actual data structures
used to implement hash tables.
This is necessary so that clients can allocate Tcl_HashTable
structures and so that macros can be used to read and write
the values of entries.
However, users of the hashing routines should never refer directly
to any of the fields of any of the hash-related data structures;
use the procedures and macros defined here.
.SH "THE TCL_HASHKEYTYPE STRUCTURE"
.PP
Extension writers can define new hash key types by defining four
procedures, initializing a Tcl_HashKeyType structure to describe
the type, and calling \fBTcl_InitCustomHashTable\fR.
The \fBTcl_HashKeyType\fR structure is defined as follows:
.CS
typedef struct Tcl_HashKeyType {
    int \fIversion\fR;
    int \fIflags\fR;
    Tcl_HashKeyProc *\fIhashKeyProc\fR;
    Tcl_CompareHashKeysProc *\fIcompareKeysProc\fR;
    Tcl_AllocHashEntryProc *\fIallocEntryProc\fR;
    Tcl_FreeHashEntryProc *\fIfreeEntryProc\fR;
} Tcl_HashKeyType;
.CE
.PP
The \fIversion\fR member is the version of the table. If this
structure is extended in future then the version can be used
to distinguish between different structures. It should be set
to \fBTCL_HASH_KEY_TYPE_VERSION\fR.
.PP
The \fIflags\fR member is one or more of the following values OR'ed together:
.IP \fBTCL_HASH_KEY_RANDOMIZE_HASH\fR 25
There are some things, pointers for example which don't hash well 
because they do not use the lower bits. If this flag is set then the
hash table will attempt to rectify this by randomising the bits and 
then using the upper N bits as the index into the table.
.PP
The \fIhashKeyProc\fR member contains the address of a function 
called to calculate a hash value for the key.
.CS
typedef unsigned int (Tcl_HashKeyProc) (
    Tcl_HashTable *\fItablePtr\fR,
    VOID *\fIkeyPtr\fR);
.CE
If this is NULL then \fIkeyPtr\fR is used and 
\fBTCL_HASH_KEY_RANDOMIZE_HASH\fR is assumed.
.PP
The \fIcompareKeysProc\fR member contains the address of a function 
called to compare two keys.
.CS
typedef int (Tcl_CompareHashKeysProc) (VOID *\fIkeyPtr\fR,
    Tcl_HashEntry *\fIhPtr\fR);
.CE
If this is NULL then the \fIkeyPtr\fR pointers are compared.
If the keys don't match then the function returns 0, otherwise
it returns 1.
.PP
The \fIallocEntryProc\fR member contains the address of a function 
called to allocate space for an entry and initialise the key.
.CS
typedef Tcl_HashEntry *(Tcl_AllocHashEntryProc) (
    Tcl_HashTable *\fItablePtr\fR, VOID *\fIkeyPtr\fR);
.CE
If this is NULL then Tcl_Alloc is used to allocate enough space for a
Tcl_HashEntry and the key pointer is assigned to key.oneWordValue.
String keys and array keys use this function to allocate enough 
space for the entry and the key in one block, rather than doing
it in two blocks. This saves space for a pointer to the key from
the entry and another memory allocation. Tcl_Obj * keys use this 
function to allocate enough space for an entry and increment the 
reference count on the object.
If 
.PP
The \fIfreeEntryProc\fR member contains the address of a function 
called to free space for an entry.
.CS
typedef void (Tcl_FreeHashEntryProc) (Tcl_HashEntry *\fIhPtr\fR);
.CE
If this is NULL then Tcl_Free is used to free the space for the 
entry. Tcl_Obj * keys use this function to decrement the
reference count on the object.
.SH KEYWORDS
hash table, key, lookup, search, value
'\"
'\" Copyright (c) 1994 The Regents of the University of California.
'\" Copyright (c) 1994-1996 Sun Microsystems, Inc.
'\" Copyright (c) 1998-1999 Scriptics Corporation
'\"
'\" See the file "license.terms" for information on usage and redistribution
'\" of this file, and for a DISCLAIMER OF ALL WARRANTIES.
'\" 
'\" RCS: @(#) $Id: RegExp.3,v 1.13 2002/11/13 22:11:40 vincentdarley Exp $
'\" 
'\" The definitions below are for supplemental macros used in Tcl/Tk
'\" manual entries.
'\"
'\" .AP type name in/out ?indent?
'\"	Start paragraph describing an argument to a library procedure.
'\"	type is type of argument (int, etc.), in/out is either "in", "out",
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'\"	needed;  use .AS below instead)
'\"
'\" .AS ?type? ?name?
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'\"	name are examples of largest possible arguments that will be passed
'\"	to .AP later.  If args are omitted, default tab stops are used.
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'\"	option's name as specified in the class command, dbName gives
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'\"
'\" .UL arg1 arg2
'\"	Print arg1 underlined, then print arg2 normally.
'\"
'\" RCS: @(#) $Id: man.macros,v 1.4 2000/08/25 06:18:32 ericm Exp $
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.TH Tcl_RegExpMatch 3 8.1 Tcl "Tcl Library Procedures"
.BS
.SH NAME
Tcl_RegExpMatch, Tcl_RegExpCompile, Tcl_RegExpExec, Tcl_RegExpRange, Tcl_GetRegExpFromObj, Tcl_RegExpMatchObj, Tcl_RegExpExecObj, Tcl_RegExpGetInfo \- Pattern matching with regular expressions
.SH SYNOPSIS
.nf
\fB#include <tcl.h>\fR
.sp
int
\fBTcl_RegExpMatchObj\fR(\fIinterp\fR, \fIstrObj\fR, \fIpatObj\fR)
.sp
int
\fBTcl_RegExpMatch\fR(\fIinterp\fR, \fIstring\fR, \fIpattern\fR)
.sp
Tcl_RegExp
\fBTcl_RegExpCompile\fR(\fIinterp\fR, \fIpattern\fR)
.sp
int
\fBTcl_RegExpExec\fR(\fIinterp\fR, \fIregexp\fR, \fIstring\fR, \fIstart\fR)
.sp
\fBTcl_RegExpRange\fR(\fIregexp\fR, \fIindex\fR, \fIstartPtr\fR, \fIendPtr\fR)
.VS 8.1
.sp
Tcl_RegExp
\fBTcl_GetRegExpFromObj\fR(\fIinterp\fR, \fIpatObj\fR, \fIcflags\fR)
.sp
int
\fBTcl_RegExpExecObj\fR(\fIinterp\fR, \fIregexp\fR, \fIobjPtr\fR, \fIoffset\fR, \fInmatches\fR, \fIeflags\fR)
.sp
\fBTcl_RegExpGetInfo\fR(\fIregexp\fR, \fIinfoPtr\fR)
.VE 8.1

.SH ARGUMENTS
.AS Tcl_Interp *interp
.AP Tcl_Interp *interp in
Tcl interpreter to use for error reporting.  The interpreter may be
NULL if no error reporting is desired.
.VS 8.1
.AP Tcl_Obj *strObj in/out
Refers to the object from which to get the string to search.  The
internal representation of the object may be converted to a form that
can be efficiently searched.
.AP Tcl_Obj *patObj in/out
Refers to the object from which to get a regular expression. The
compiled regular expression is cached in the object.
.VE 8.1
.AP char *string in
String to check for a match with a regular expression.
.AP "CONST char" *pattern in
String in the form of a regular expression pattern.
.AP Tcl_RegExp regexp in
Compiled regular expression.  Must have been returned previously
by \fBTcl_GetRegExpFromObj\fR or \fBTcl_RegExpCompile\fR.
.AP char *start in
If \fIstring\fR is just a portion of some other string, this argument
identifies the beginning of the larger string.
If it isn't the same as \fIstring\fR, then no \fB^\fR matches
will be allowed.
.AP int index in
Specifies which range is desired:  0 means the range of the entire
match, 1 or greater means the range that matched a parenthesized
sub-expression.
.VS 8.4
.AP "CONST char" **startPtr out
The address of the first character in the range is stored here, or
NULL if there is no such range.
.AP "CONST char" **endPtr out
The address of the character just after the last one in the range
is stored here, or NULL if there is no such range.
.VE 8.4
.VS 8.1
.AP int cflags in
OR-ed combination of compilation flags. See below for more information.
.AP Tcl_Obj *objPtr in/out
An object which contains the string to check for a match with a
regular expression.
.AP int offset in
The character offset into the string where matching should begin.
The value of the offset has no impact on \fB^\fR matches.  This
behavior is controlled by \fIeflags\fR.
.AP int nmatches in
The number of matching subexpressions that should be remembered for
later use.  If this value is 0, then no subexpression match
information will be computed.  If the value is -1, then
all of the matching subexpressions will be remembered.  Any other
value will be taken as the maximum number of subexpressions to
remember.
.AP int eflags in
OR-ed combination of the values TCL_REG_NOTBOL and TCL_REG_NOTEOL.
See below for more information.
.AP Tcl_RegExpInfo *infoPtr out
The address of the location where information about a previous match
should be stored by \fBTcl_RegExpGetInfo\fR.
.VE 8.1
.BE

.SH DESCRIPTION
.PP
\fBTcl_RegExpMatch\fR determines whether its \fIpattern\fR argument
matches \fIregexp\fR, where \fIregexp\fR is interpreted
as a regular expression using the rules in the \fBre_syntax\fR
reference page. 
If there is a match then \fBTcl_RegExpMatch\fR returns 1.
If there is no match then \fBTcl_RegExpMatch\fR returns 0.
If an error occurs in the matching process (e.g. \fIpattern\fR
is not a valid regular expression) then \fBTcl_RegExpMatch\fR
returns \-1 and leaves an error message in the interpreter result.
.VS 8.1.2
\fBTcl_RegExpMatchObj\fR is similar to \fBTcl_RegExpMatch\fR except it
operates on the Tcl objects \fIstrObj\fR and \fIpatObj\fR instead of
UTF strings. 
\fBTcl_RegExpMatchObj\fR is generally more efficient than
\fBTcl_RegExpMatch\fR, so it is the preferred interface.
.VE 8.1.2
.PP
\fBTcl_RegExpCompile\fR, \fBTcl_RegExpExec\fR, and \fBTcl_RegExpRange\fR
provide lower-level access to the regular expression pattern matcher.
\fBTcl_RegExpCompile\fR compiles a regular expression string into
the internal form used for efficient pattern matching.
The return value is a token for this compiled form, which can be
used in subsequent calls to \fBTcl_RegExpExec\fR or \fBTcl_RegExpRange\fR.
If an error occurs while compiling the regular expression then
\fBTcl_RegExpCompile\fR returns NULL and leaves an error message
in the interpreter result.
Note:  the return value from \fBTcl_RegExpCompile\fR is only valid
up to the next call to \fBTcl_RegExpCompile\fR;  it is not safe to
retain these values for long periods of time.
.PP
\fBTcl_RegExpExec\fR executes the regular expression pattern matcher.
It returns 1 if \fIstring\fR contains a range of characters that
match \fIregexp\fR, 0 if no match is found, and
\-1 if an error occurs.
In the case of an error, \fBTcl_RegExpExec\fR leaves an error
message in the interpreter result.
When searching a string for multiple matches of a pattern,
it is important to distinguish between the start of the original
string and the start of the current search.
For example, when searching for the second occurrence of a
match, the \fIstring\fR argument might point to the character
just after the first match;  however, it is important for the
pattern matcher to know that this is not the start of the entire string,
so that it doesn't allow \fB^\fR atoms in the pattern to match.
The \fIstart\fR argument provides this information by pointing
to the start of the overall string containing \fIstring\fR.
\fIStart\fR will be less than or equal to \fIstring\fR;  if it
is less than \fIstring\fR then no \fB^\fR matches will be allowed.
.PP
\fBTcl_RegExpRange\fR may be invoked after \fBTcl_RegExpExec\fR
returns;  it provides detailed information about what ranges of
the string matched what parts of the pattern.
\fBTcl_RegExpRange\fR returns a pair of pointers in \fI*startPtr\fR
and \fI*endPtr\fR that identify a range of characters in
the source string for the most recent call to \fBTcl_RegExpExec\fR.
\fIIndex\fR indicates which of several ranges is desired:
if \fIindex\fR is 0, information is returned about the overall range
of characters that matched the entire pattern;  otherwise,
information is returned about the range of characters that matched the
\fIindex\fR'th parenthesized subexpression within the pattern.
If there is no range corresponding to \fIindex\fR then NULL
is stored in \fI*startPtr\fR and \fI*endPtr\fR.
.PP
.VS 8.1
\fBTcl_GetRegExpFromObj\fR, \fBTcl_RegE3e4e5e6e7e8e9e:expExecObj\fR, and
\fBTcl_RegExpGetInfo\fR are object interfaces that provide the most
direct control of Henry Spencer's regular expression library.  For
users that need to modify compilation and execution options directly,
it is recommended that you use these interfaces instead of calling the
internal regexp functions.  These interfaces handle the details of UTF
to Unicode translations as well as providing improved performance
through caching in the pattern and string objects.
.PP
\fBTcl_GetRegExpFromObj\fR attempts to return a compiled regular
expression from the \fIpatObj\fR.  If the object does not already
contain a compiled regular expression it will attempt to create one
from the string in the object and assign it to the internal
representation of the \fIpatObj\fR.  The return value of this function
is of type \fBTcl_RegExp\fR.  The return value is a token for this
compiled form, which can be used in subsequent calls to
\fBTcl_RegExpExecObj\fR or \fBTcl_RegExpGetInfo\fR.  If an error
occurs while compiling the regular expression then
\fBTcl_GetRegExpFromObj\fR returns NULL and leaves an error message in
the interpreter result.  The regular expression token can be used as
long as the internal representation of \fIpatObj\fR refers to the
compiled form.  The \fIeflags\fR argument is a bitwise OR of
zero or more of the following flags that control the compilation of
\fIpatObj\fR:
.RS 2
.TP
\fBTCL_REG_ADVANCED\fR
Compile advanced regular expressions (`AREs').  This mode corresponds to
the normal regular expression syntax accepted by the Tcl regexp and
regsub commands.
.TP
\fBTCL_REG_EXTENDED\fR
Compile extended regular expressions (`EREs').  This mode corresponds
to the regular expression syntax recognized by Tcl 8.0 and earlier
versions. 
.TP
\fBTCL_REG_BASIC\fR
Compile basic regular expressions (`BREs').  This mode corresponds
to the regular expression syntax recognized by common Unix utilities
like \fBsed\fR and \fBgrep\fR.  This is the default if no flags are
specified.
.TP
\fBTCL_REG_EXPANDED\fR
Compile the regular expression (basic, extended, or advanced) using an
expanded syntax that allows comments and whitespace.  This mode causes
non-backslashed non-bracket-expression white
space and #-to-end-of-line comments to be ignored.
.TP
\fBTCL_REG_QUOTE\fR
Compile a literal string, with all characters treated as ordinary characters.
.TP
\fBTCL_REG_NOCASE\fR
Compile for matching that ignores upper/lower case distinctions.
.TP
\fBTCL_REG_NEWLINE\fR
Compile for newline-sensitive matching.  By default, newline is a
completely ordinary character with no special meaning in either
regular expressions or strings.  With this flag, `[^' bracket
expressions and `.' never match newline, `^' matches an empty string
after any newline in addition to its normal function, and `$' matches
an empty string before any newline in addition to its normal function.
\fBREG_NEWLINE\fR is the bitwise OR of \fBREG_NLSTOP\fR and
\fBREG_NLANCH\fR.
.TP
\fBTCL_REG_NLSTOP\fR
Compile for partial newline-sensitive matching,
with the behavior of
`[^' bracket expressions and `.' affected,
but not the behavior of `^' and `$'.  In this mode, `[^' bracket
expressions and `.' never match newline.
.TP
\fBTCL_REG_NLANCH\fR
Compile for inverse partial newline-sensitive matching,
with the behavior of
of `^' and `$' (the ``anchors'') affected, but not the behavior of
`[^' bracket expressions and `.'.  In this mode `^' matches an empty string
after any newline in addition to its normal function, and `$' matches
an empty string before any newline in addition to its normal function.
.TP
\fBTCL_REG_NOSUB\fR
Compile for matching that reports only success or failure,
not what was matched.  This reduces compile overhead and may improve
performance.  Subsequent calls to \fBTcl_RegExpGetInfo\fR or
\fBTcl_RegExpRange\fR will not report any match information.
.TP
\fBTCL_REG_CANMATCH\fR
Compile for matching that reports the potential to complete a partial
match given more text (see below).
.RE
.PP
Only one of
\fBTCL_REG_EXTENDED\fR,
\fBTCL_REG_ADVANCED\fR,
\fBTCL_REG_BASIC\fR, and
\fBTCL_REG_QUOTE\fR may be specified.
.PP
\fBTcl_RegExpExecObj\fR executes the regular expression pattern
matcher.  It returns 1 if \fIobjPtr\fR contains a range of characters
that match \fIregexp\fR, 0 if no match is found, and \-1 if an error
occurs.  In the case of an error, \fBTcl_RegExpExecObj\fR leaves an
error message in the interpreter result.  The \fInmatches\fR value
indicates to the matcher how many subexpressions are of interest.  If
\fInmatches\fR is 0, then no subexpression match information is
recorded, which may allow the matcher to make various optimizations.
If the value is -1, then all of the subexpressions in the pattern are
remembered.  If the value is a positive integer, then only that number
of subexpressions will be remembered.  Matching begins at the
specified Unicode character index given by \fIoffset\fR.  Unlike
\fBTcl_RegExpExec\fR, the behavior of anchors is not affected by the
offset value.  Instead the behavior of the anchors is explicitly
controlled by the \fIeflags\fR argument, which is a bitwise OR of
zero or more of the following flags:
.RS 2
.TP
\fBTCL_REG_NOTBOL\fR
The starting character will not be treated as the beginning of a
line or the beginning of the string, so `^' will not match there.
Note that this flag has no effect on how `\fB\eA\fR' matches.
.TP
\fBTCL_REG_NOTEOL\fR
The last character in the string will not be treated as the end of a
line or the end of the string, so '$' will not match there.
Note that this flag has no effect on how `\fB\eZ\fR' matches.
.RE
.PP
\fBTcl_RegExpGetInfo\fR retrieves information about the last match
performed with a given regular expression \fIregexp\fR.  The
\fIinfoPtr\fR argument contains a pointer to a structure that is
defined as follows:
.PP
.CS
typedef struct Tcl_RegExpInfo {
	int \fInsubs\fR;
	Tcl_RegExpIndices *\fImatches\fR;
	long \fIextendStart\fR;
} Tcl_RegExpInfo;
.CE
.PP
The \fInsubs\fR field contains a count of the number of parenthesized
subexpressions within the regular expression.  If the \fBTCL_REG_NOSUB\fR
was used, then this value will be zero.  The \fImatches\fR field
points to an array of \fInsubs\fR values that indicate the bounds of each
subexpression matched.  The first element in the array refers to the
range matched by the entire regular expression, and subsequent elements
refer to the parenthesized subexpressions in the order that they
appear in the pattern.  Each element is a structure that is defined as
follows:
.PP
.CS
typedef struct Tcl_RegExpIndices {
	long \fIstart\fR;
	long \fIend\fR;
} Tcl_RegExpIndices;
.CE
.PP
The \fIstart\fR and \fIend\fR values are Unicode character indices
relative to the offset location within \fIobjPtr\fR where matching began.
The \fIstart\fR index identifies the first character of the matched
subexpression.  The \fIend\fR index identifies the first character
after the matched subexpression.  If the subexpression matched the
empty string, then \fIstart\fR and \fIend\fR will be equal.  If the
subexpression did not participate in the match, then \fIstart\fR and
\fIend\fR will be set to -1.
.PP
The \fIextendStart\fR field in \fBTcl_RegExpInfo\fR is only set if the
\fBTCL_REG_CANMATCH\fR flag was used.  It indicates the first
character in the string where a match could occur.  If a match was
found, this will be the same as the beginning of the current match.
If no match was found, then it indicates the earliest point at which a
match might occur if additional text is appended to the string.  If it
is no match is possible even with further text, this field will be set 
to -1.
.VE 8.1
.SH "SEE ALSO"
re_syntax(n)
.SH KEYWORDS
match, pattern, regular expression, string, subexpression, Tcl_RegExpIndices, Tcl_RegExpInfo
'\"
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'\" 
'\" The definitions below are for supplemental macros used in Tcl/Tk
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Command-Line Name:	\\fB\\$1\\fR
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