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.
- 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.
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_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.
KEYWORDS¶
backslash, convert, element, list, merge, split, strings