tcl_splitlist(3)

NAME

Tcl_SplitList, Tcl_Merge, Tcl_ScanElement, Tcl_ConvertEle
ment, Tcl_ScanCountedElement, Tcl_ConvertCountedElement manipulate Tcl lists

SYNOPSIS

#include <tcl.h>
int
Tcl_SplitList(interp, list, argcPtr, argvPtr)
char *
Tcl_Merge(argc, argv)
int
Tcl_ScanElement(src, flagsPtr)
int
Tcl_ScanCountedElement(src, length, flagsPtr)
int
Tcl_ConvertElement(src, dst, flags)
int
Tcl_ConvertCountedElement(src, length, dst, flags)

ARGUMENTS

Tcl_Interp *interp (out) Interpreter to

use for error
reporting. If
NULL, then no
error message
is left.

char *list (in) Pointer to a

string with
proper list
structure.

int *argcPtr (out) Filled in with

number of ele
ments in list.

CONST char ***argvPtr (out) *argvPtr will

be filled in
with the
address of an
array of
pointers to
the strings
that are the
extracted ele
ments of list.
There will be
*argcPtr valid entries in the
array, fol
lowed by a
NULL entry.

int argc (in) Number of ele

ments in argv.

CONST char * CONST *argv (in) Array of

strings to
merge together
into a single
list. Each
string will
become a sepa
rate element
of the list.

CONST char *src (in) String that is

to become an
element of a
list.

int *flagsPtr (in) Pointer to

word to fill
in with infor
mation about
src. The
value of
*flagsPtr must be passed to
Tcl_Con
vertElement.

int length (in) Number of

bytes in
string src.

char *dst (in) Place to copy

converted list
element. Must
contain enough
characters to
hold converted
string.

int flags (in) Information

about src.
Must be value
returned by
previous call
to
Tcl_ScanEle ment, possibly
OR-ed with
TCL_DONT_USE_BRACES.

DESCRIPTION

These procedures may be used to disassemble and reassemble
Tcl lists. Tcl_SplitList breaks a list up into its con stituent elements, returning an array of pointers to the
elements using argcPtr and argvPtr. While extracting the arguments, Tcl_SplitList obeys the usual rules for back slash substitutions and braces. The area of memory
pointed to by *argvPtr is dynamically allocated; in addi tion to the array of pointers, it also holds copies of all
the list elements. It is the caller's responsibility to
free up all of this storage. For example, suppose that
you have called Tcl_SplitList with the following code:

int argc, code;
char *string;
char **argv;
...
code = Tcl_SplitList(interp, string, &argc, &argv);

Then you should eventually free the storage with a call
like the following:

Tcl_Free((char *) argv);

Tcl_SplitList normally returns TCL_OK, which means the list was successfully parsed. If there was a syntax error
in list, then TCL_ERROR is returned and the interpreter's result will point to an error message describing the prob
lem (if interp was not NULL). If TCL_ERROR is returned then no memory is allocated and *argvPtr is not modified.

Tcl_Merge is the inverse of Tcl_SplitList: it takes a collection of strings given by argc and argv and generates a result string that has proper list structure. This
means that commands like index may be used to extract the
original elements again. In addition, if the result of
Tcl_Merge is passed to Tcl_Eval, it will be parsed into argc words whose values will be the same as the argv strings passed to Tcl_Merge. Tcl_Merge will modify the list elements with braces and/or backslashes in order to
produce proper Tcl list structure. The result string is
dynamically allocated using Tcl_Alloc; the caller must eventually release the space using Tcl_Free.

If the result of Tcl_Merge is passed to Tcl_SplitList, the elements returned by Tcl_SplitList will be identical to those passed into Tcl_Merge. However, the converse is not true: if Tcl_SplitList is passed a given string, and the resulting argc and argv are passed to Tcl_Merge, the resulting string may not be the same as the original
string passed to Tcl_SplitList. This is because Tcl_Merge may use backslashes and braces differently than the origi
nal string.

Tcl_ScanElement and Tcl_ConvertElement are the procedures that do all of the real work of Tcl_Merge. Tcl_ScanEle ment scans its src argument and determines how to use backslashes and braces when converting it to a list ele
ment. It returns an overestimate of the number of charac
ters required to represent src as a list element, and it
stores information in *flagsPtr that is needed by Tcl_Con vertElement.

Tcl_ConvertElement is a companion procedure to Tcl_ScanElement. It does the actual work of converting a string to a list element. Its flags argument must be the
same as the value returned by Tcl_ScanElement. Tcl_Con vertElement writes a proper list element to memory start ing at *dst and returns a count of the total number of
characters written, which will be no more than the result
returned by Tcl_ScanElement. Tcl_ConvertElement writes out only the actual list element without any leading or
trailing spaces: it is up to the caller to include spaces
between adjacent list elements.

Tcl_ConvertElement uses one of two different approaches to handle the special characters in src. Wherever possible,
it handles special characters by surrounding the string
with braces. This produces clean-looking output, but
can't be used in some situations, such as when src con
tains unmatched braces. In these situations,
Tcl_ConvertElement handles special characters by generat ing backslash sequences for them. The caller may insist
on the second approach by OR-ing the flag value returned
by Tcl_ScanElement with TCL_DONT_USE_BRACES. Although this will produce an uglier result, it is useful in some
special situations, such as when Tcl_ConvertElement is being used to generate a portion of an argument for a Tcl
command. In this case, surrounding src with curly braces
would cause the command not to be parsed correctly.

Tcl_ScanCountedElement and Tcl_ConvertCountedElement are the same as Tcl_ScanElement and Tcl_ConvertElement, except the length of string src is specified by the length argu ment, and the string may contain embedded nulls.

KEYWORDS

backslash, convert, element, list, merge, split, strings

Tcl 8.0 Tcl_SplitList(3)