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Tcl_BooleanObj

Section: Tcl Library Procedures (3)
Updated: 8.5
Index Return to Main Contents

NAME

Tcl_NewBooleanObj, Tcl_SetBooleanObj, Tcl_GetBooleanFromObj - store/retrieve boolean value in a Tcl_Obj

SYNOPSIS

#include <tcl.h>

Tcl_Obj *
Tcl_NewBooleanObj(intValue)

Tcl_SetBooleanObj(objPtr, intValue)

int
Tcl_GetBooleanFromObj(interp, objPtr, intPtr)

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.

int *intPtr (out) Points to place where Tcl_GetBooleanFromObj stores the boolean value (0 or 1) obtained from objPtr.

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 no-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 intPtr. 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 intPtr and if that value is no-zero a 1 is written at the address given by intPtr. In all cases where a value is written at the address given by intPtr, 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.

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.