plucky (3) Tcl_ScanElement.3tcl.gz
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)
Tcl_Size
Tcl_ScanElement(src, flagsPtr)
Tcl_Size
Tcl_ScanCountedElement(src, length, flagsPtr)
Tcl_Size
Tcl_ConvertElement(src, dst, flags)
Tcl_Size
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.
Tcl_Size | int *argcPtr (out) Filled in with number of elements in list. May be (Tcl_Size
*)NULL when not used. If it points to a variable which type is
not Tcl_Size, a compiler warning will be generated. If your
extensions is compiled with -DTCL_8_API, this function will
return TCL_ERROR for lists with more than INT_MAX elements
(which should trigger proper error-handling), otherwise expect
it to crash.
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.
Tcl_Size 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.
Tcl_Size 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:
Tcl_Size argc;
int 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(argv);
Tcl_SplitList normally returns TCL_OK, which means the list was successfully parsed. If sizePtr points to
a variable of type int and the list contains more than 2**31 key/value pairs, or 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(3tcl)
KEYWORDS
backslash, convert, element, list, merge, split, strings