Tcl_SplitList(3) Tcl Library Procedures Tcl_SplitList(3)

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NAME

Tcl_SplitList, Tcl_Merge, Tcl_ScanElement, Tcl_ConvertElement,
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.

const char *list (in) Pointer to a string with
proper list structure.

int *argcPtr (out) Filled in with number of
elements 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 elements of
list. There will be
*argcPtr valid entries in
the array, followed by a
NULL entry.

int argc (in) Number of elements in
argv.

const char *const *argv (in) Array of strings to merge
together into a single
list. Each string will
become a separate 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 information about
src. The value of
*flagsPtr must be passed
to Tcl_ConvertElement.

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_ScanElement, possibly
OR-ed with
TCL_DONT_USE_BRACES.
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DESCRIPTION

These procedures may be used to disassemble and reassemble Tcl lists.
Tcl_SplitList breaks a list up into its constituent elements,
returning an array of pointers to the elements using argcPtr and
argvPtr. While extracting the arguments, Tcl_SplitList obeys the
usual rules for backslash substitutions and braces. The area of
memory pointed to by *argvPtr is dynamically allocated; in addition
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 problem (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 original string.

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

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_ConvertElement writes a proper list element to
memory starting 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 cannot be used in some situations, such as
when src contains unmatched braces. In these situations,
Tcl_ConvertElement handles special characters by generating 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.

By default, Tcl_ConvertElement will use quoting in its output to be
sure the first character of an element is not the hash character
("#".) This is to be sure the first element of any list passed to
eval is not mis-parsed as the beginning of a comment. When a list
element is not the first element of a list, this quoting is not
necessary. When the caller can be sure that the element is not the
first element of a list, it can disable quoting of the leading hash
character by OR-ing the flag value returned by Tcl_ScanElement with
TCL_DONT_QUOTE_HASH.

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 argument, and the string may contain
embedded nulls.

SEE ALSO

Tcl_ListObjGetElements(3)

KEYWORDS

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

Tcl 8.0 Tcl_SplitList(3)