Tcl_BooleanObj C API

Store/retrieve boolean value in a Tcl_Obj

Also documents Tcl_NewBooleanObj, Tcl_SetBooleanObj, Tcl_GetBooleanFromObj, Tcl_GetBoolFromObj

literal type exactly as shown argument replace with your value ~~?optional?~~ may be omitted

Synopsis#

#include <tcl.h>

Tcl_Obj * Tcl_NewBooleanObj(intValue)#

Tcl_SetBooleanObj(objPtr, intValue)#

int Tcl_GetBooleanFromObj(interp, objPtr, boolPtr)#

int Tcl_GetBoolFromObj(interp, objPtr, flags. charPtr)#

Arguments#

int intValue (in): Integer value to be stored as a boolean value in a Tcl_Obj.
Tcl_Obj *objPtr (in/out): Points to the Tcl_Obj in which to store, or from which to retrieve a boolean value.
Tcl_Interp *interp (in/out): If a boolean value cannot be retrieved, an error message is left in the interpreter's result value unless interp is NULL.
bool | int *boolPtr (out): Points to place where Tcl_GetBooleanFromObj stores the boolean value (0 or 1) obtained from objPtr.
char *charPtr (out): Points to place where Tcl_GetBoolFromObj stores the boolean value (0 or 1) obtained from objPtr.
int flags (in): 0 or TCL_NULL_OK. If TCL_NULL_OK is used, then the empty string or NULL will result in Tcl_GetBoolFromObj return TCL_OK, the *charPtr filled with the value '\xFF';

Description#

These procedures are used to pass boolean values to and from Tcl as Tcl_Obj's. When storing a boolean value into a Tcl_Obj, any non-zero integer value in intValue is taken to be the boolean value 1, and the integer value 0 is taken to be the boolean value 0.

Tcl_NewBooleanObj creates a new Tcl_Obj, stores the boolean value intValue in it, and returns a pointer to the new Tcl_Obj. The new Tcl_Obj has reference count of zero.

Tcl_SetBooleanObj accepts objPtr, a pointer to an existing Tcl_Obj, and stores in the Tcl_Obj *objPtr the boolean value intValue. This is a write operation on *objPtr, so objPtr must be unshared. Attempts to write to a shared Tcl_Obj will panic. A successful write of intValue into *objPtr implies the freeing of any former value stored in *objPtr.

Tcl_GetBooleanFromObj attempts to retrieve a boolean value from the value stored in *objPtr. If objPtr holds a string value recognized by Tcl_GetBoolean, then the recognized boolean value is written at the address given by boolPtr. If objPtr holds any value recognized as a number by Tcl, then if that value is zero a 0 is written at the address given by boolPtr and if that value is non-zero a 1 is written at the address given by boolPtr. In all cases where a value is written at the address given by boolPtr, Tcl_GetBooleanFromObj returns TCL_OK. If the value of objPtr does not meet any of the conditions above, then TCL_ERROR is returned and an error message is left in the interpreter's result unless interp is NULL. Tcl_GetBooleanFromObj may also make changes to the internal fields of *objPtr so that future calls to Tcl_GetBooleanFromObj on the same objPtr can be performed more efficiently.

Tcl_GetBoolFromObj functions almost the same as Tcl_GetBooleanFromObj, but it has an additional parameter flags, which can be used to specify whether the empty string or NULL is accepted as valid.

Note that the routines Tcl_GetBooleanFromObj and Tcl_GetBoolean are not functional equivalents. The set of values for which Tcl_GetBooleanFromObj will return TCL_OK is strictly larger than the set of values for which Tcl_GetBoolean will do the same. For example, the value “5” passed to Tcl_GetBooleanFromObj will lead to a TCL_OK return (and the boolean value 1), while the same value passed to Tcl_GetBoolean will lead to a TCL_ERROR return.

Reference count management#

Tcl_NewBooleanObj always returns a zero-reference object, much like Tcl_NewObj.

Tcl_SetBooleanObj does not modify the reference count of its objPtr argument, but does require that the object be unshared.

Tcl_GetBooleanFromObj does not modify the reference count of its objPtr argument; it only reads. Note however that this function may set the interpreter result; if that is the only place that is holding a reference to the object, it will be deleted.

Keywords#

boolean · value