#include <tcl_utils.h>char *w(char *str);char *vw(char *fmt, ...);
These functions return strings held in writable memory. Writable strings are
required in the arguments of many Tcl functions, including Tcl_SetVar
and Tcl_GetKeyedListField. The arguments specify the string the return
as writable. For w() this is simply an exact copy of the argument. For
vw() the returned string is a formatted copy of the input, which is
specified in the standard printf style.
The return value from the w function isvalid only until the next call
of w(). Similarly for the vw function.
Examples of usage are:
Tcl_GetKeyedListField(interp, vw("MODE%d", mode_num), gap_defs, &buf);
Tcl_SetVar(interp, w("arr(element)"), "10", TCL_GLOBAL_ONLY);
NOTE: In the current implementations both functions have a limit of handling 8192 bytes per call.