Tcl_SetVar(3)
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NAME
Tcl_SetVar, Tcl_SetVar2, Tcl_GetVar, Tcl_GetVar2,
Tcl_UnsetVar, Tcl_UnsetVar2 - manipulate Tcl variables
SYNOPSIS
#include <<tcl.h>>
char *
Tcl_SetVar(interp, varName, newValue, flags)
char *
Tcl_SetVar2(interp, name1, name2, newValue, flags)
char *
Tcl_GetVar(interp, varName, flags)
char *
Tcl_GetVar2(interp, name1, name2, flags)
int
Tcl_UnsetVar(interp, varName, flags)
int
Tcl_UnsetVar2(interp, name1, name2, flags)
ARGUMENTS
Tcl_Interp *interp (in) Interpreter containing
variable.
char *varName (in) Name of variable. May
include a series of ::
namespace qualifiers to
specify a variable in a
particular namespace.
May refer to a scalar
variable or an element
of an array variable.
If the name references
an element of an array,
then it must be in
writable memory: Tcl
will make temporary
modifications to it
while looking up the
name.
char *newValue (in) New value for variable.
int flags (in) OR-ed combination of
bits providing addi-
tional information for
operation. See below
for valid values.
char *name1 (in) Name of scalar vari-
able, or name of array
variable if name2 is
non-NULL. May include
a series of :: names-
pace qualifiers to
specify a variable in a
particular namespace.
char *name2 (in) If non-NULL, gives name
of element within array
and name1 must refer to
an array variable.
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DESCRIPTION
These procedures may be used to create, modify, read, and
delete Tcl variables from C code.
Note that Tcl_GetVar and Tcl_SetVar have been largely
replaced by the object-based procedures Tcl_ObjGetVar2 and
Tcl_ObjSetVar2. Those object-based procedures read, mod-
ify, and create a variable whose name is held in a Tcl
object instead of a string. They also return a pointer to
the object which is the variable's value instead of
returning a string. Operations on objects can be faster
since objects hold an internal representation that can be
manipulated more efficiently.
Tcl_SetVar and Tcl_SetVar2 will create a new variable or
modify an existing one. Both of these procedures set the
given variable to the value given by newValue, and they
return a pointer to a copy of the variable's new value,
which is stored in Tcl's variable structure. Tcl keeps a
private copy of the variable's value, so the caller may
change newValue after these procedures return without
affecting the value of the variable. If an error occurs
in setting the variable (e.g. an array variable is refer-
enced without giving an index into the array), they return
NULL.
The name of the variable may be specified to Tcl_SetVar
and Tcl_SetVar2 in either of two ways. If Tcl_SetVar is
called, the variable name is given as a single string,
varName. If varName 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 varName doesn't have parentheses as described above,
then the entire string is treated as the name of a scalar
variable. If Tcl_SetVar2 is called, then the array name
and index have been separated by the caller into two sepa-
rate strings, name1 and name2 respectively; if name2 is
zero it means that a scalar variable is being referenced.
The flags argument may be used to specify any of several
options to the procedures. It consists of an OR-ed combi-
nation of the following bits. Note that the flag bit
TCL_PARSE_PART1 is only meaningful for the procedures
Tcl_SetVar2 and Tcl_GetVar2.
TCL_GLOBAL_ONLY
Under normal circumstances the procedures look up
variables as follows: If a procedure call is active
in interp, a variable is looked up at the current
level of procedure call. Otherwise, a variable is
looked up first in the current namespace, then in
the global namespace. However, if this bit is set
in flags then the variable is looked up only in the
global namespace even if there is a procedure call
active. If both TCL_GLOBAL_ONLY and TCL_NAMES-
PACE_ONLY are given, TCL_GLOBAL_ONLY is ignored.
TCL_NAMESPACE_ONLY
Under normal circumstances the procedures look up
variables as follows: If a procedure call is active
in interp, a variable is looked up at the current
level of procedure call. Otherwise, a variable is
looked up first in the current namespace, then in
the global namespace. However, if this bit is set
in flags then the variable is looked up only in the
current namespace even if there is a procedure call
active.
TCL_LEAVE_ERR_MSG
If an error is returned and this bit is set in
flags, then an error message will be left in the
interpreter's result, where it can be retrieved
with Tcl_GetObjResult or Tcl_GetStringResult. If
this flag bit isn't set then no error message is
left and the interpreter's result will not be modi-
fied.
TCL_APPEND_VALUE
If this bit is set then newValue is appended to the
current value, instead of replacing it. If the
variable is currently undefined, then this bit is
ignored.
TCL_LIST_ELEMENT
If this bit is set, then newValue 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 sub-
list (i.e. the variable's current value is empty,
or contains the single character ``{'', or ends in
`` }'').
TCL_PARSE_PART1
If this bit is set when calling Tcl_SetVar2 and
Tcl_GetVar2, name1 may contain both an array and an
element name: if the name contains an open paren-
thesis and ends with a close parenthesis, then the
value between the parentheses is treated as an ele-
ment name (which can have any string value) and the
characters before the first open parenthesis are
treated as the name of an array variable. If the
flag TCL_PARSE_PART1 is given, name2 should be NULL
since the array and element names are taken from
name1.
Tcl_GetVar and Tcl_GetVar2 return the current value of a
variable. The arguments to these procedures are treated
in the same way as the arguments to Tcl_SetVar and
Tcl_SetVar2. 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 Tcl_SetVar or Tcl_SetVar2). Tcl_GetVar and
Tcl_GetVar2 use the flag bits TCL_GLOBAL_ONLY and
TCL_LEAVE_ERR_MSG, both of which have the same meaning as
for Tcl_SetVar. In addition, Tcl_GetVar2 uses the bit
TCL_PARSE_PART1, which has the same meaning as for
Tcl_SetVar2. If an error occurs in reading the variable
(e.g. the variable doesn't exist or an array element is
specified for a scalar variable), then NULL is returned.
Tcl_UnsetVar and Tcl_UnsetVar2 may be used to remove a
variable, so that future calls to Tcl_GetVar or Tcl_Get-
Var2 for the variable will return an error. The arguments
to these procedures are treated in the same way as the
arguments to Tcl_GetVar and Tcl_GetVar2. If the variable
is successfully removed then TCL_OK is returned. If the
variable cannot be removed because it doesn't exist then
TCL_ERROR 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.
SEE ALSO
Tcl_GetObjResult, Tcl_GetStringResult, Tcl_ObjGetVar2,
Tcl_ObjSetVar2, Tcl_TraceVar
KEYWORDS
array, interpreter, object, scalar, set, unset, variable