Ubuntu Manpage: Tcl_NewBooleanObj, Tcl_SetBooleanObj, Tcl_GetBooleanFromObj, Tcl_GetBoolFromObj

Provided by: tcl9.0-doc_9.0.1+dfsg-1_all

NAME

       Tcl_NewBooleanObj,  Tcl_SetBooleanObj, Tcl_GetBooleanFromObj, Tcl_GetBoolFromObj - 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, 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';
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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