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


#include <tcl.h>

Tcl_Obj *

Tcl_SetBooleanObj(objPtr, boolValue)

(interp, objPtr, boolPtr)


int boolValue (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 object unless interp is NULL.

int *boolPtr (out)

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



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 boolValue 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 boolValue 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 boolValue. 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 boolValue 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.

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.


Tcl_NewObj, Tcl_IsShared, Tcl_GetBoolean


boolean, object


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