man/man3/DString.3

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.TH Tcl_DString 3 7.4 Tcl "Tcl Library Procedures"
.BS
.SH NAME
Tcl_DStringInit, Tcl_DStringAppend, Tcl_DStringAppendElement, Tcl_DStringStartSublist, Tcl_DStringEndSublist, Tcl_DStringLength, Tcl_DStringValue, Tcl_DStringSetLength, Tcl_DStringTrunc, Tcl_DStringFree, Tcl_DStringResult, Tcl_DStringGetResult \- manipulate dynamic strings
.SH SYNOPSIS
.nf
\fB#include <tcl.h>\fR
.sp
\fBTcl_DStringInit\fR(\fIdsPtr\fR)
.sp
char *
\fBTcl_DStringAppend\fR(\fIdsPtr, string, length\fR)
.sp
char *
\fBTcl_DStringAppendElement\fR(\fIdsPtr, string\fR)
.sp
\fBTcl_DStringStartSublist\fR(\fIdsPtr\fR)
.sp
\fBTcl_DStringEndSublist\fR(\fIdsPtr\fR)
.sp
int
\fBTcl_DStringLength\fR(\fIdsPtr\fR)
.sp
char *
\fBTcl_DStringValue\fR(\fIdsPtr\fR)
.sp
\fBTcl_DStringSetLength\fR(\fIdsPtr, newLength\fR)
.sp
\fBTcl_DStringTrunc\fR(\fIdsPtr, newLength\fR)
.sp
\fBTcl_DStringFree\fR(\fIdsPtr\fR)
.sp
\fBTcl_DStringResult\fR(\fIinterp, dsPtr\fR)
.sp
\fBTcl_DStringGetResult\fR(\fIinterp, dsPtr\fR)
.SH ARGUMENTS
.AS Tcl_DString newLength
.AP Tcl_DString *dsPtr in/out
Pointer to structure that is used to manage a dynamic string.
.AP "CONST char" *string in
Pointer to characters to add to dynamic string.
.AP int length in
Number of characters from string to add to dynamic string.  If -1,
add all characters up to null terminating character.
.AP int newLength in
New length for dynamic string, not including null terminating
character.
.AP Tcl_Interp *interp in/out
Interpreter whose result is to be set from or moved to the
dynamic string.
.BE

.SH DESCRIPTION
.PP
Dynamic strings provide a mechanism for building up arbitrarily long
strings by gradually appending information.  If the dynamic string is
short then there will be no memory allocation overhead;  as the string
gets larger, additional space will be allocated as needed.
.PP
\fBTcl_DStringInit\fR initializes a dynamic string to zero length.
The Tcl_DString structure must have been allocated by the caller.
No assumptions are made about the current state of the structure;
anything already in it is discarded.
If the structure has been used previously, \fBTcl_DStringFree\fR should
be called first to free up any memory allocated for the old
string.
.PP
\fBTcl_DStringAppend\fR adds new information to a dynamic string,
allocating more memory for the string if needed.
If \fIlength\fR is less than zero then everything in \fIstring\fR
is appended to the dynamic string;  otherwise \fIlength\fR
specifies the number of bytes to append.
\fBTcl_DStringAppend\fR returns a pointer to the characters of
the new string.  The string can also be retrieved from the
\fIstring\fR field of the Tcl_DString structure.
.PP
\fBTcl_DStringAppendElement\fR is similar to \fBTcl_DStringAppend\fR
except that it doesn't take a \fIlength\fR argument (it appends
all of \fIstring\fR) and it converts the string to a proper list element
before appending.
\fBTcl_DStringAppendElement\fR adds a separator space before the
new list element unless the new list element is the first in a
list or sub-list (i.e. either the current string is empty, or it
contains the single character ``{'', or the last two characters of
the current string are `` {'').
\fBTcl_DStringAppendElement\fR returns a pointer to the
characters of the new string.
.PP
\fBTcl_DStringStartSublist\fR and \fBTcl_DStringEndSublist\fR can be
used to create nested lists.
To append a list element that is itself a sublist, first
call \fBTcl_DStringStartSublist\fR, then call \fBTcl_DStringAppendElement\fR
for each of the elements in the sublist, then call
\fBTcl_DStringEndSublist\fR to end the sublist.
\fBTcl_DStringStartSublist\fR appends a space character if needed,
followed by an open brace;  \fBTcl_DStringEndSublist\fR appends
a close brace.
Lists can be nested to any depth.
.PP
\fBTcl_DStringLength\fR is a macro that returns the current length
of a dynamic string (not including the terminating null character).
\fBTcl_DStringValue\fR is a  macro that returns a pointer to the
current contents of a dynamic string.
.PP
.PP
\fBTcl_DStringSetLength\fR changes the length of a dynamic string.
If \fInewLength\fR is less than the string's current length, then
the string is truncated.
If \fInewLength\fR is greater than the string's current length,
then the string will become longer and new space will be allocated
for the string if needed.
However, \fBTcl_DStringSetLength\fR will not initialize the new
space except to provide a terminating null character;  it is up to the
caller to fill in the new space.
\fBTcl_DStringSetLength\fR does not free up the string's storage space
even if the string is truncated to zero length, so \fBTcl_DStringFree\fR
will still need to be called.
.PP
\fBTcl_DStringTrunc\fR changes the length of a dynamic string.
This procedure is now deprecated.  \fBTcl_DStringSetLength\fR  should
be used instead.
.PP
\fBTcl_DStringFree\fR should be called when you're finished using
the string.  It frees up any memory that was allocated for the string
and reinitializes the string's value to an empty string.
.PP
\fBTcl_DStringResult\fR sets the result of \fIinterp\fR to the value of
the dynamic string given by \fIdsPtr\fR.  It does this by moving
a pointer from \fIdsPtr\fR to the interpreter's result.
This saves the cost of allocating new memory and copying the string.
\fBTcl_DStringResult\fR also reinitializes the dynamic string to
an empty string.
.PP
\fBTcl_DStringGetResult\fR does the opposite of \fBTcl_DStringResult\fR.
It sets the value of \fIdsPtr\fR to the result of \fIinterp\fR and
it clears \fIinterp\fR's result.
If possible it does this by moving a pointer rather than by copying
the string.

.SH KEYWORDS
append, dynamic string, free, result