## Tcl8.6.2/Tk8.6.2 Documentation > Tcl C API, version 8.6.2 > ListObj

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  NAME
    Tcl_ListObjAppendList, Tcl_ListObjAppendElement, Tcl_NewListObj, Tcl_SetListObj, Tcl_ListObjGetElements, Tcl_ListObjLength, Tcl_ListObjIndex, Tcl_ListObjReplace — manipulate Tcl values as lists
  SYNOPSIS
    #include <tcl.h>
    int
    Tcl_ListObjAppendList(interp, listPtr, elemListPtr)
    int
    Tcl_ListObjAppendElement(interp, listPtr, objPtr)
    Tcl_Obj *
    Tcl_NewListObj(objc, objv)
    Tcl_SetListObj(objPtr, objc, objv)
    int
    Tcl_ListObjGetElements(interp, listPtr, objcPtr, objvPtr)
    int
    Tcl_ListObjLength(interp, listPtr, intPtr)
    int
    Tcl_ListObjIndex(interp, listPtr, index, objPtrPtr)
    int
    Tcl_ListObjReplace(interp, listPtr, first, count, objc, objv)
  ARGUMENTS
  DESCRIPTION
  SEE ALSO
  KEYWORDS

### NAME

Tcl_ListObjAppendList, Tcl_ListObjAppendElement, Tcl_NewListObj, Tcl_SetListObj, Tcl_ListObjGetElements, Tcl_ListObjLength, Tcl_ListObjIndex, Tcl_ListObjReplace — manipulate Tcl values as lists

### SYNOPSIS

#include <tcl.h>
int
Tcl_ListObjAppendList(interp, listPtr, elemListPtr)
int
Tcl_ListObjAppendElement(interp, listPtr, objPtr)
Tcl_Obj *
Tcl_NewListObj(objc, objv)
Tcl_SetListObj(objPtr, objc, objv)
int
Tcl_ListObjGetElements(interp, listPtr, objcPtr, objvPtr)
int
Tcl_ListObjLength(interp, listPtr, intPtr)
int
Tcl_ListObjIndex(interp, listPtr, index, objPtrPtr)
int
Tcl_ListObjReplace(interp, listPtr, first, count, objc, objv)

### ARGUMENTS

Tcl_Interp *interp (in)
  If an error occurs while converting a value to be a list value, an error message is left in the interpreter's result value unless interp is NULL.

Tcl_Obj *listPtr (in/out)
  Points to the list value to be manipulated. If listPtr does not already point to a list value, an attempt will be made to convert it to one.

Tcl_Obj *elemListPtr (in/out)
  For Tcl_ListObjAppendList, this points to a list value containing elements to be appended onto listPtr. Each element of *elemListPtr will become a new element of listPtr. If *elemListPtr is not NULL and does not already point to a list value, an attempt will be made to convert it to one.

Tcl_Obj *objPtr (in)
  For Tcl_ListObjAppendElement, points to the Tcl value that will be appended to listPtr. For Tcl_SetListObj, this points to the Tcl value that will be converted to a list value containing the objc elements of the array referenced by objv.

int *objcPtr (in)
  Points to location where Tcl_ListObjGetElements stores the number of element values in listPtr.

Tcl_Obj ***objvPtr (out)
  A location where Tcl_ListObjGetElements stores a pointer to an array of pointers to the element values of listPtr.

int objc (in)
  The number of Tcl values that Tcl_NewListObj will insert into a new list value, and Tcl_ListObjReplace will insert into listPtr. For Tcl_SetListObj, the number of Tcl values to insert into objPtr.

Tcl_Obj *const objv[] (in)
  An array of pointers to values. Tcl_NewListObj will insert these values into a new list value and Tcl_ListObjReplace will insert them into an existing listPtr. Each value will become a separate list element.

int *intPtr (out)
  Points to location where Tcl_ListObjLength stores the length of the list.

int index (in)
  Index of the list element that Tcl_ListObjIndex is to return. The first element has index 0.

Tcl_Obj **objPtrPtr (out)
  Points to place where Tcl_ListObjIndex is to store a pointer to the resulting list element value.

int first (in)
  Index of the starting list element that Tcl_ListObjReplace is to replace. The list's first element has index 0.

int count (in)
  The number of elements that Tcl_ListObjReplace is to replace.

### DESCRIPTION

Tcl list values 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 values from C code.

Tcl_ListObjAppendList and Tcl_ListObjAppendElement both add one or more values to the end of the list value referenced by listPtr. Tcl_ListObjAppendList appends each element of the list value referenced by elemListPtr while Tcl_ListObjAppendElement appends the single value referenced by objPtr. Both procedures will convert the value referenced by listPtr to a list value if necessary. If an error occurs during conversion, both procedures return TCL_ERROR and leave an error message in the interpreter's result value if interp is not NULL. Similarly, if elemListPtr does not already refer to a list value, Tcl_ListObjAppendList will attempt to convert it to one and if an error occurs during conversion, will return TCL_ERROR and leave an error message in the interpreter's result value if interp is not NULL. Both procedures invalidate any old string representation of listPtr and, if it was converted to a list value, free any old internal representation. Similarly, Tcl_ListObjAppendList frees any old internal representation of elemListPtr if it converts it to a list value. After appending each element in elemListPtr, Tcl_ListObjAppendList increments the element's reference count since listPtr now also refers to it. For the same reason, Tcl_ListObjAppendElement increments objPtr's reference count. If no error occurs, the two procedures return TCL_OK after appending the values.

Tcl_NewListObj and Tcl_SetListObj create a new value or modify an existing value to hold the objc elements of the array referenced by objv where each element is a pointer to a Tcl value. If objc is less than or equal to zero, they return an empty value. The new value's string representation is left invalid. The two procedures increment the reference counts of the elements in objc since the list value now refers to them. The new list value returned by Tcl_NewListObj has reference count zero.

Tcl_ListObjGetElements returns a count and a pointer to an array of the elements in a list value. It returns the count by storing it in the address objcPtr. Similarly, it returns the array pointer by storing it in the address objvPtr. The memory pointed to is managed by Tcl and should not be freed or written to by the caller. If the list is empty, 0 is stored at objcPtr and NULL at objvPtr. If listPtr is not already a list value, Tcl_ListObjGetElements will attempt to convert it to one; if the conversion fails, it returns TCL_ERROR and leaves an error message in the interpreter's result value if interp is not NULL. Otherwise it returns TCL_OK after storing the count and array pointer.

Tcl_ListObjLength returns the number of elements in the list value referenced by listPtr. It returns this count by storing an integer in the address intPtr. If the value is not already a list value, Tcl_ListObjLength will attempt to convert it to one; if the conversion fails, it returns TCL_ERROR and leaves an error message in the interpreter's result value if interp is not NULL. Otherwise it returns TCL_OK after storing the list's length.

The procedure Tcl_ListObjIndex returns a pointer to the value at element index in the list referenced by listPtr. It returns this value by storing a pointer to it in the address objPtrPtr. If listPtr does not already refer to a list value, Tcl_ListObjIndex will attempt to convert it to one; if the conversion fails, it returns TCL_ERROR and leaves an error message in the interpreter's result value if interp is not NULL. If the index is out of range, that is, index is negative or greater than or equal to the number of elements in the list, Tcl_ListObjIndex stores a NULL in objPtrPtr and returns TCL_OK. Otherwise it returns TCL_OK after storing the element's value 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.

Tcl_ListObjReplace replaces zero or more elements of the list referenced by listPtr with the objc values in the array referenced by objv. If listPtr does not point to a list value, Tcl_ListObjReplace will attempt to convert it to one; if the conversion fails, it returns TCL_ERROR and leaves an error message in the interpreter's result value if interp is not NULL. Otherwise, it returns TCL_OK after replacing the values. If objv is NULL, no new elements are added. If the argument first is zero or negative, it refers to the first element. If first 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. count gives the number of elements to replace. If count is zero or negative then no elements are deleted; the new elements are simply inserted before the one designated by first. Tcl_ListObjReplace invalidates listPtr's old string representation. The reference counts of any elements inserted from objv are incremented since the resulting list now refers to them. Similarly, the reference counts for any replaced values are decremented.

Because Tcl_ListObjReplace combines both element insertion and deletion, it can be used to implement a number of list operations. For example, the following code inserts the objc values referenced by the array of value pointers objv just before the element index of the list referenced by listPtr:

    result = Tcl_ListObjReplace(interp, listPtr, index, 0,
            objc, objv);

Similarly, the following code appends the objc values referenced by the array objv to the end of the list listPtr:

    result = Tcl_ListObjLength(interp, listPtr, &length);
    if (result == TCL_OK) {
        result = Tcl_ListObjReplace(interp, listPtr, length, 0,
                objc, objv);
    }

The count list elements starting at first can be deleted by simply calling Tcl_ListObjReplace with a NULL objvPtr:

    result = Tcl_ListObjReplace(interp, listPtr, first, count,
            0, NULL);

### SEE ALSO

Tcl_NewObj, Tcl_DecrRefCount, Tcl_IncrRefCount, Tcl_GetObjResult

### KEYWORDS

append, index, insert, internal representation, length, list, list value, list type, value, value type, replace, string representation
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