Tcl_SplitList(3) Tcl Library Procedures Tcl_SplitList(3)
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
Interpreter to use for error reporting. If NULL, then no error message
is left. Pointer to a string with proper list structure. Filled in
with number of elements in list. *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. Number of elements in argv. Array of
strings to merge together into a single list. Each string will become
a separate element of the list. String that is to become an element of
a list. Pointer to word to fill in with information about src. The
value of *flagsPtr must be passed to Tcl_ConvertElement. Number of
bytes in string src. Place to copy converted list element. Must con-
tain enough characters to hold converted string. Information about
src. Must be value returned by previous call to Tcl_ScanElement, possi-
bly 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 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 back-
slash substitutions and braces. The area of memory pointed to by
*argvPtr is dynamically allocated; in addition to the array of point-
ers, 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 suc-
cessfully 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_ScanEle-
ment. Tcl_ConvertElement writes a proper list element to memory start-
ing at *dst and returns a count of the total number of characters writ-
ten, 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 char-
acters 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 embed-
ded nulls.
KEYWORDS
backslash, convert, element, list, merge, split, strings
Tcl 8.0 Tcl_SplitList(3)
SplitList 8.5.4 - Generated Thu Aug 21 06:07:55 CDT 2008