Tcl_SplitList(interp, list, argcPtr, argvPtr)
Tcl_ScanCountedElement(src, length, flagsPtr)
Tcl_ConvertElement(src, dst, flags)
Tcl_ConvertCountedElement(src, length, dst, flags)
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 callers
responsibility to free up all of this storage.
For example, suppose that you have called Tcl_SplitList with
the following code:
Then you should eventually free the storage with a call like the
int argc, code;
code = Tcl_SplitList(interp, string, &argc, &argv);
Tcl_Free((char *) argv);
Tcl_SplitList normally returns TCL_OK, which means the list was
If there was a syntax error in list, then TCL_ERROR is returned
and the interpreters 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
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
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
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
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
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
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.