Tcl_Merge
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.
char *list (in) Pointer to a string with proper
list structure.
int *argcPtr (out) Filled in with number of elements
in list.
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.
char **argv (in) Array of strings to merge together
into a single list. Each string
will become a separate element of
the list.
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 ele-
ment. Must contain enough charac-
ters 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 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 fol-
lowing:
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
written, which will be no more than the result returned by Tcl_ScanEle-
ment. Tcl_ConvertElement writes out only the actual list element with-
out 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 can't 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.
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)
