path: root/doc/SetVar.3

'\"
'\" Copyright (c) 1989-1993 The Regents of the University of California.
'\" Copyright (c) 1994-1997 Sun Microsystems, Inc.
'\"
'\" See the file "license.terms" for information on usage and redistribution
'\" of this file, and for a DISCLAIMER OF ALL WARRANTIES.
'\"
.TH Tcl_SetVar 3 8.1 Tcl "Tcl Library Procedures"
.so man.macros
.BS
.SH NAME
Tcl_SetVar2Ex, Tcl_SetVar, Tcl_SetVar2, Tcl_ObjSetVar2, Tcl_GetVar2Ex, Tcl_GetVar, Tcl_GetVar2, Tcl_ObjGetVar2, Tcl_UnsetVar, Tcl_UnsetVar2 \- manipulate Tcl variables
.SH SYNOPSIS
.nf
\fB#include <tcl.h>\fR
.sp
Tcl_Obj *
\fBTcl_SetVar2Ex\fR(\fIinterp, name1, name2, newValuePtr, flags\fR)
.sp
const char *
\fBTcl_SetVar\fR(\fIinterp, varName, newValue, flags\fR)
.sp
const char *
\fBTcl_SetVar2\fR(\fIinterp, name1, name2, newValue, flags\fR)
.sp
Tcl_Obj *
\fBTcl_ObjSetVar2\fR(\fIinterp, part1Ptr, part2Ptr, newValuePtr, flags\fR)
.sp
Tcl_Obj *
\fBTcl_GetVar2Ex\fR(\fIinterp, name1, name2, flags\fR)
.sp
const char *
\fBTcl_GetVar\fR(\fIinterp, varName, flags\fR)
.sp
const char *
\fBTcl_GetVar2\fR(\fIinterp, name1, name2, flags\fR)
.sp
Tcl_Obj *
\fBTcl_ObjGetVar2\fR(\fIinterp, part1Ptr, part2Ptr, flags\fR)
.sp
int
\fBTcl_UnsetVar\fR(\fIinterp, varName, flags\fR)
.sp
int
\fBTcl_UnsetVar2\fR(\fIinterp, name1, name2, flags\fR)
.SH ARGUMENTS
.AS Tcl_Interp *newValuePtr
.AP Tcl_Interp *interp in
Interpreter containing variable.
.AP "const char" *name1 in
Contains the name of an array variable (if \fIname2\fR is non-NULL)
or (if \fIname2\fR is NULL) either the name of a scalar variable
or a complete name including both variable name and index.
May include \fB::\fR namespace qualifiers
to specify a variable in a particular namespace.
.AP "const char" *name2 in
If non-NULL, gives name of element within array; in this
case \fIname1\fR must refer to an array variable.
.AP Tcl_Obj *newValuePtr in
Points to a Tcl value containing the new value for the variable.
.AP int flags in
OR-ed combination of bits providing additional information. See below
for valid values.
.AP "const char" *varName in
Name of variable.
May include \fB::\fR namespace qualifiers
to specify a variable in a particular namespace.
May refer to a scalar variable or an element of
an array.
.AP "const char" *newValue in
New value for variable, specified as a null-terminated string.
A copy of this value is stored in the variable.
.AP Tcl_Obj *part1Ptr in
Points to a Tcl value containing the variable's name.
The name may include a series of \fB::\fR namespace qualifiers
to specify a variable in a particular namespace.
May refer to a scalar variable or an element of an array variable.
.AP Tcl_Obj *part2Ptr in
If non-NULL, points to a value containing the name of an element
within an array and \fIpart1Ptr\fR must refer to an array variable.
.BE

.SH DESCRIPTION
.PP
These procedures are used to create, modify, read, and delete
Tcl variables from C code.
.PP
\fBTcl_SetVar2Ex\fR, \fBTcl_SetVar\fR, \fBTcl_SetVar2\fR, and
\fBTcl_ObjSetVar2\fR
will create a new variable or modify an existing one.
These procedures set the given variable to the value
given by \fInewValuePtr\fR or \fInewValue\fR and return a
pointer to the variable's new value, which is stored in Tcl's
variable structure.
\fBTcl_SetVar2Ex\fR and \fBTcl_ObjSetVar2\fR take the new value as a
Tcl_Obj and return
a pointer to a Tcl_Obj.  \fBTcl_SetVar\fR and \fBTcl_SetVar2\fR
take the new value as a string and return a string; they are
usually less efficient than \fBTcl_ObjSetVar2\fR.  Note that the
return value may be different than the \fInewValuePtr\fR or
\fInewValue\fR argument, due to modifications made by write traces.
If an error occurs in setting the variable (e.g. an array
variable is referenced without giving an index into the array)
NULL is returned and an error message is left in \fIinterp\fR's
result if the \fBTCL_LEAVE_ERR_MSG\fR \fIflag\fR bit is set.
.PP
\fBTcl_GetVar2Ex\fR, \fBTcl_GetVar\fR, \fBTcl_GetVar2\fR, and
\fBTcl_ObjGetVar2\fR
return the current value of a variable.
The arguments to these procedures are treated in the same way
as the arguments to the procedures described above.
Under normal circumstances, the return value is a pointer
to the variable's value.  For \fBTcl_GetVar2Ex\fR and
\fBTcl_ObjGetVar2\fR the value is
returned as a pointer to a Tcl_Obj.  For \fBTcl_GetVar\fR and
\fBTcl_GetVar2\fR the value is returned as a string; this is
usually less efficient, so \fBTcl_GetVar2Ex\fR or \fBTcl_ObjGetVar2\fR
are preferred.
If an error occurs while reading the variable (e.g. the variable
does not exist or an array element is specified for a scalar
variable), then NULL is returned and an error message is left
in \fIinterp\fR's result if the \fBTCL_LEAVE_ERR_MSG\fR \fIflag\fR
bit is set.
.PP
\fBTcl_UnsetVar\fR and \fBTcl_UnsetVar2\fR may be used to remove
a variable, so that future attempts to read the variable will return
an error.
The arguments to these procedures are treated in the same way
as the arguments to the procedures above.
If the variable is successfully removed then \fBTCL_OK\fR is returned.
If the variable cannot be removed because it does not exist then
\fBTCL_ERROR\fR is returned and an error message is left
in \fIinterp\fR's result if the \fBTCL_LEAVE_ERR_MSG\fR \fIflag\fR
bit is set.
If an array element is specified, the given element is removed
but the array remains.
If an array name is specified without an index, then the entire
array is removed.
.PP
The name of a variable may be specified to these procedures in
four ways:
.IP [1]
If \fBTcl_SetVar\fR, \fBTcl_GetVar\fR, or \fBTcl_UnsetVar\fR
is invoked, the variable name is given as
a single string, \fIvarName\fR.
If \fIvarName\fR contains an open parenthesis and ends with a
close parenthesis, then the value between the parentheses is
treated as an index (which can have any string value) and
the characters before the first open
parenthesis are treated as the name of an array variable.
If \fIvarName\fR does not have parentheses as described above, then
the entire string is treated as the name of a scalar variable.
.IP [2]
If the \fIname1\fR and \fIname2\fR arguments are provided and
\fIname2\fR is non-NULL, then an array element is specified and
the array name and index have
already been separated by the caller: \fIname1\fR contains the
name and \fIname2\fR contains the index.  An error is generated
if \fIname1\fR  contains an open parenthesis and ends with a
close parenthesis (array element) and \fIname2\fR is non-NULL.
.IP [3]
If \fIname2\fR is NULL, \fIname1\fR is treated just like
\fIvarName\fR in case [1] above (it can be either a scalar or an array
element variable name).
.PP
The \fIflags\fR argument may be used to specify any of several
options to the procedures.
It consists of an OR-ed combination of the following bits.
.TP
\fBTCL_GLOBAL_ONLY\fR
Under normal circumstances the procedures look up variables as follows.
If a procedure call is active in \fIinterp\fR,
the variable is looked up at the current level of procedure call.
Otherwise, the variable is looked up first in the current namespace,
then in the global namespace.
However, if this bit is set in \fIflags\fR then the variable
is looked up only in the global namespace
even if there is a procedure call active.
If both \fBTCL_GLOBAL_ONLY\fR and \fBTCL_NAMESPACE_ONLY\fR are given,
\fBTCL_GLOBAL_ONLY\fR is ignored.
.TP
\fBTCL_NAMESPACE_ONLY\fR
If this bit is set in \fIflags\fR then the variable
is looked up only in the current namespace; if a procedure is active
its variables are ignored, and the global namespace is also ignored unless
it is the current namespace.
.TP
\fBTCL_LEAVE_ERR_MSG\fR
If an error is returned and this bit is set in \fIflags\fR, then
an error message will be left in the interpreter's result,
where it can be retrieved with \fBTcl_GetObjResult\fR
or \fBTcl_GetStringResult\fR.
If this flag bit is not set then no error message is left
and the interpreter's result will not be modified.
.TP
\fBTCL_APPEND_VALUE\fR
If this bit is set then \fInewValuePtr\fR or \fInewValue\fR is
appended to the current value instead of replacing it.
If the variable is currently undefined, then the bit is ignored.
This bit is only used by the \fBTcl_Set*\fR procedures.
.TP
\fBTCL_LIST_ELEMENT\fR
If this bit is set, then \fInewValue\fR is converted to a valid
Tcl list element before setting (or appending to) the variable.
A separator space is appended before the new list element unless
the list element is going to be the first element in a list or
sublist (i.e. the variable's current value is empty, or contains
the single character
.QW { ,
or ends in
.QW " }" ).
When appending, the original value of the variable must also be
a valid list, so that the operation is the appending of a new
list element onto a list.
.PP
\fBTcl_GetVar\fR and \fBTcl_GetVar2\fR
return the current value of a variable.
The arguments to these procedures are treated in the same way
as the arguments to \fBTcl_SetVar\fR and \fBTcl_SetVar2\fR.
Under normal circumstances, the return value is a pointer
to the variable's value (which is stored in Tcl's variable
structure and will not change before the next call to \fBTcl_SetVar\fR
or \fBTcl_SetVar2\fR).
\fBTcl_GetVar\fR and \fBTcl_GetVar2\fR use the flag bits \fBTCL_GLOBAL_ONLY\fR
and \fBTCL_LEAVE_ERR_MSG\fR, both of
which have
the same meaning as for \fBTcl_SetVar\fR.
If an error occurs in reading the variable (e.g. the variable
does not exist or an array element is specified for a scalar
variable), then NULL is returned.
.PP
\fBTcl_UnsetVar\fR and \fBTcl_UnsetVar2\fR may be used to remove
a variable, so that future calls to \fBTcl_GetVar\fR or \fBTcl_GetVar2\fR
for the variable will return an error.
The arguments to these procedures are treated in the same way
as the arguments to \fBTcl_GetVar\fR and \fBTcl_GetVar2\fR.
If the variable is successfully removed then \fBTCL_OK\fR is returned.
If the variable cannot be removed because it does not exist then
\fBTCL_ERROR\fR is returned.
If an array element is specified, the given element is removed
but the array remains.
If an array name is specified without an index, then the entire
array is removed.

.SH "REFERENCE COUNT MANAGEMENT"
.PP
The result of \fBTcl_SetVar2Ex\fR, \fBTcl_ObjSetVar2\fR, \fBTcl_GetVar2Ex\fR,
and \fBTcl_ObjGetVar2\fR is (if non-NULL) a value with a reference of at least
1, where that reference is held by the variable that the function has just
operated upon.
.PP
The \fInewValuePtr\fR argument to \fBTcl_SetVar2Ex\fR and \fBTcl_ObjSetVar2\fR
may be an arbitrary reference count value.  Its reference count is
incremented on success.  On failure, if its reference count is zero, it is
decremented and freed so the caller need do nothing with it.
.PP
The \fIpart1Ptr\fR argument to \fBTcl_ObjSetVar2\fR and \fBTcl_ObjGetVar2\fR can
have any reference count.  These functions never modify it.
.PP
The \fIpart2Ptr\fR argument to \fBTcl_ObjSetVar2\fR and \fBTcl_ObjGetVar2\fR, if
non-NULL, should not have a zero reference count as these functions may
retain a reference to it, particularly when it is used to create an array
element that did not previously exist, and decrementing the reference count
later would leave them pointing to a freed Tcl_Obj.

.SH "SEE ALSO"
Tcl_GetObjResult, Tcl_GetStringResult, Tcl_TraceVar

.SH KEYWORDS
array, get variable, interpreter, scalar, set, unset, value, variable