man/man3/Tcl_ListObjLength.3

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.TH Tcl_ListObj 3 8.0 Tcl "Tcl Library Procedures"
.BS
.SH NAME
Tcl_ListObjAppendList, Tcl_ListObjAppendElement, Tcl_NewListObj, Tcl_SetListObj, Tcl_ListObjGetElements, Tcl_ListObjLength, Tcl_ListObjIndex, Tcl_ListObjReplace \- manipulate Tcl objects as lists
.SH SYNOPSIS
.nf
\fB#include <tcl.h>\fR
.sp
int
\fBTcl_ListObjAppendList\fR(\fIinterp, listPtr, elemListPtr\fR)
.sp
int
\fBTcl_ListObjAppendElement\fR(\fIinterp, listPtr, objPtr\fR)
.sp
Tcl_Obj *
\fBTcl_NewListObj\fR(\fIobjc, objv\fR)
.sp
\fBTcl_SetListObj\fR(\fIobjPtr, objc, objv\fR)
.sp
int
\fBTcl_ListObjGetElements\fR(\fIinterp, listPtr, objcPtr, objvPtr\fR)
.sp
int
\fBTcl_ListObjLength\fR(\fIinterp, listPtr, intPtr\fR)
.sp
int
\fBTcl_ListObjIndex\fR(\fIinterp, listPtr, index, objPtrPtr\fR)
.sp
int
\fBTcl_ListObjReplace\fR(\fIinterp, listPtr, first, count, objc, objv\fR)
.SH ARGUMENTS
.AS Tcl_Interp "*CONST objv[]" out
.AP Tcl_Interp *interp in
If an error occurs while converting an object to be a list object,
an error message is left in the interpreter's result object
unless \fIinterp\fR is NULL.
.AP Tcl_Obj *listPtr in/out
Points to the list object to be manipulated.
If \fIlistPtr\fR does not already point to a list object,
an attempt will be made to convert it to one.
.AP Tcl_Obj *elemListPtr in/out
For \fBTcl_ListObjAppendList\fR, this points to a list object
containing elements to be appended onto \fIlistPtr\fR.
Each element of *\fIelemListPtr\fR will
become a new element of \fIlistPtr\fR.
If *\fIelemListPtr\fR is not NULL and
does not already point to a list object,
an attempt will be made to convert it to one.
.AP Tcl_Obj *objPtr in
For \fBTcl_ListObjAppendElement\fR,
points to the Tcl object that will be appended to \fIlistPtr\fR.
For \fBTcl_SetListObj\fR,
this points to the Tcl object that will be converted to a list object
containing the \fIobjc\fR elements of the array referenced by \fIobjv\fR.
.AP int *objcPtr in
Points to location where \fBTcl_ListObjGetElements\fR
stores the number of element objects in \fIlistPtr\fR.
.AP Tcl_Obj ***objvPtr out
A location where \fBTcl_ListObjGetElements\fR stores a pointer to an array
of pointers to the element objects of \fIlistPtr\fR.  
.AP int objc in
The number of Tcl objects that \fBTcl_NewListObj\fR
will insert into a new list object,
and \fBTcl_ListObjReplace\fR will insert into \fIlistPtr\fR.
For \fBTcl_SetListObj\fR,
the number of Tcl objects to insert into \fIobjPtr\fR.
.VS
.AP Tcl_Obj	"*CONST\ objv[]" in
An array of pointers to objects.
\fBTcl_NewListObj\fR will insert these objects into a new list object
and \fBTcl_ListObjReplace\fR will insert them into an existing \fIlistPtr\fR.
Each object will become a separate list element.  
.VE
.AP int *intPtr out
Points to location where \fBTcl_ListObjLength\fR
stores the length of the list.
.AP int index in
Index of the list element that \fBTcl_ListObjIndex\fR
is to return.
The first element has index 0.
.AP Tcl_Obj **objPtrPtr out
Points to place where \fBTcl_ListObjIndex\fR is to store
a pointer to the resulting list element object.
.AP int first in
Index of the starting list element that \fBTcl_ListObjReplace\fR
is to replace.
The list's first element has index 0.
.AP int count in
The number of elements that \fBTcl_ListObjReplace\fR
is to replace.
.BE

.SH DESCRIPTION
.PP
Tcl list objects have an internal representation that supports
the efficient indexing and appending.
The procedures described in this man page are used to
create, modify, index, and append to Tcl list objects from C code.
.PP
\fBTcl_ListObjAppendList\fR and \fBTcl_ListObjAppendElement\fR
both add one or more objects
to the end of the list object referenced by \fIlistPtr\fR.
\fBTcl_ListObjAppendList\fR appends each element of the list object
referenced by \fIelemListPtr\fR while
\fBTcl_ListObjAppendElement\fR appends the single object
referenced by \fIobjPtr\fR.
Both procedures will convert the object referenced by \fIlistPtr\fR
to a list object if necessary.
If an error occurs during conversion,
both procedures return \fBTCL_ERROR\fR and leave an error message
in the interpreter's result object if \fIinterp\fR is not NULL.
Similarly, if \fIelemListPtr\fR does not already refer to a list object,
\fBTcl_ListObjAppendList\fR will attempt to convert it to one
and if an error occurs during conversion,
will return \fBTCL_ERROR\fR
and leave an error message in the interpreter's result object
if interp is not NULL.
Both procedures invalidate any old string representation of \fIlistPtr\fR
and, if it was converted to a list object,
free any old internal representation.
Similarly, \fBTcl_ListObjAppendList\fR frees any old internal representation
of \fIelemListPtr\fR if it converts it to a list object.
After appending each element in \fIelemListPtr\fR,
\fBTcl_ListObjAppendList\fR increments the element's reference count
since \fIlistPtr\fR now also refers to it.
For the same reason, \fBTcl_ListObjAppendElement\fR
increments \fIobjPtr\fR's reference count.
If no error occurs,
the two procedures return \fBTCL_OK\fR after appending the objects.
.PP
\fBTcl_NewListObj\fR and \fBTcl_SetListObj\fR
create a new object or modify an existing object to hold 
the \fIobjc\fR elements of the array referenced by \fIobjv\fR
where each element is a pointer to a Tcl object.
If \fIobjc\fR is less than or equal to zero,
they return an empty object.
The new object's string representation is left invalid.
The two procedures increment the reference counts
of the elements in \fIobjc\fR since the list object now refers to them.
The new list object returned by \fBTcl_NewListObj\fR
has reference count zero.
.PP
\fBTcl_ListObjGetElements\fR returns a count and a pointer to an array of
the elements in a list object.  It returns the count by storing it in the
address \fIobjcPtr\fR.  Similarly, it returns the array pointer by storing
it in the address \fIobjvPtr\fR.
The memory pointed to is managed by Tcl and should not be freed by the
caller.
If \fIlistPtr\fR is not already a list object, \fBTcl_ListObjGetElements\fR
will attempt to convert it to one; if the conversion fails, it returns
\fBTCL_ERROR\fR and leaves an error message in the interpreter's result
object if \fIinterp\fR is not NULL.
Otherwise it returns \fBTCL_OK\fR after storing the count and array pointer.
.PP
\fBTcl_ListObjLength\fR returns the number of elements in the list object
referenced by \fIlistPtr\fR.
It returns this count by storing an integer in the address \fIintPtr\fR.
If the object is not already a list object,
\fBTcl_ListObjLength\fR will attempt to convert it to one;
if the conversion fails, it returns \fBTCL_ERROR\fR
and leaves an error message in the interpreter's result object
if \fIinterp\fR is not NULL.
Otherwise it returns \fBTCL_OK\fR after storing the list's length.
.PP
The procedure \fBTcl_ListObjIndex\fR returns a pointer to the object
at element \fIindex\fR in the list referenced by \fIlistPtr\fR.
It returns this object by storing a pointer to it
in the address \fIobjPtrPtr\fR.
If \fIlistPtr\fR does not already refer to a list object,
\fBTcl_ListObjIndex\fR will attempt to convert it to one;
if the conversion fails, it returns \fBTCL_ERROR\fR
and leaves an error message in the interpreter's result object
if \fIinterp\fR is not NULL.
If the index is out of range,
that is, \fIindex\fR is negative or
greater than or equal to the number of elements in the list,
\fBTcl_ListObjIndex\fR stores a NULL in \fIobjPtrPtr\fR
and returns \fBTCL_OK\fR.
Otherwise it returns \fBTCL_OK\fR after storing the element's
object pointer.
The reference count for the list element is not incremented;
the caller must do that if it needs to retain a pointer to the element.
.PP
\fBTcl_ListObjReplace\fR replaces zero or more elements
of the list referenced by \fIlistPtr\fR
with the \fIobjc\fR objects in the array referenced by \fIobjv\fR.
If \fIlistPtr\fR does not point to a list object,
\fBTcl_ListObjReplace\fR will attempt to convert it to one;
if the conversion fails, it returns \fBTCL_ERROR\fR
and leaves an error message in the interpreter's result object
if \fIinterp\fR is not NULL.
Otherwise, it returns \fBTCL_OK\fR after replacing the objects.
If \fIobjv\fR is NULL, no new elements are added.
If the argument \fIfirst\fR is zero or negative,
it refers to the first element.
If \fIfirst\fR is greater than or equal to the
number of elements in the list, then no elements are deleted;
the new elements are appended to the list.
\fIcount\fR gives the number of elements to replace.
If \fIcount\fR is zero or negative then no elements are deleted;
the new elements are simply inserted before the one
designated by \fIfirst\fR.
\fBTcl_ListObjReplace\fR invalidates \fIlistPtr\fR's
old string representation.
The reference counts of any elements inserted from \fIobjv\fR
are incremented since the resulting list now refers to them.
Similarly, the reference counts for any replaced objects are decremented.
.PP
Because \fBTcl_ListObjReplace\fR combines
both element insertion and deletion,
it can be used to implement a number of list operations.
For example, the following code inserts the \fIobjc\fR objects
referenced by the array of object pointers \fIobjv\fR
just before the element \fIindex\fR of the list referenced by \fIlistPtr\fR:
.CS
result = Tcl_ListObjReplace(interp, listPtr, index, 0, objc, objv);
.CE
Similarly, the following code appends the \fIobjc\fR objects
referenced by the array \fIobjv\fR
to the end of the list \fIlistPtr\fR:
.CS
result = Tcl_ListObjLength(interp, listPtr, &length);
if (result == TCL_OK) {
	result = Tcl_ListObjReplace(interp, listPtr, length, 0, objc, objv);
}
.CE
The \fIcount\fR list elements starting at \fIfirst\fR can be deleted
by simply calling \fBTcl_ListObjReplace\fR
with a NULL \fIobjvPtr\fR:
.CS
result = Tcl_ListObjReplace(interp, listPtr, first, count, 0, NULL);
.CE

.SH "SEE ALSO"
Tcl_NewObj, Tcl_DecrRefCount, Tcl_IncrRefCount, Tcl_GetObjResult

.SH KEYWORDS
append, index, insert, internal representation, length, list, list object, list type, object, object type, replace, string representation