source: downloads/tcl8.5.2/doc/ExprLongObj.3 @ 35

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.so man.macros
.TH Tcl_ExprLongObj 3 8.0 Tcl "Tcl Library Procedures"
.BS
.SH NAME
Tcl_ExprLongObj, Tcl_ExprDoubleObj, Tcl_ExprBooleanObj, Tcl_ExprObj \- evaluate an expression
.SH SYNOPSIS
.nf
\fB#include <tcl.h>\fR
.sp
int
\fBTcl_ExprLongObj\fR(\fIinterp, objPtr, longPtr\fR)
.sp
int
\fBTcl_ExprDoubleObj\fR(\fIinterp, objPtr, doublePtr\fR)
.sp
int
\fBTcl_ExprBooleanObj\fR(\fIinterp, objPtr, booleanPtr\fR)
.sp
int
\fBTcl_ExprObj\fR(\fIinterp, objPtr, resultPtrPtr\fR)
.SH ARGUMENTS
.AS Tcl_Interp **resultPtrPtr out
.AP Tcl_Interp *interp in
Interpreter in whose context to evaluate \fIobjPtr\fR.
.AP Tcl_Obj *objPtr in
Pointer to an object containing the expression to evaluate.
.AP long *longPtr out
Pointer to location in which to store the integer value of the
expression.
.AP int *doublePtr out
Pointer to location in which to store the floating-point value of the
expression.
.AP int *booleanPtr out
Pointer to location in which to store the 0/1 boolean value of the
expression.
.AP Tcl_Obj **resultPtrPtr out
Pointer to location in which to store a pointer to the object
that is the result of the expression.
.BE

.SH DESCRIPTION
.PP
These four procedures all evaluate an expression, returning
the result in one of four different forms.
The expression is given by the \fIobjPtr\fR argument, and it
can have any of the forms accepted by the \fBexpr\fR command.
.PP
The \fIinterp\fR argument refers to an interpreter used to
evaluate the expression (e.g. for variables and nested Tcl
commands) and to return error information.
.PP
For all of these procedures the return value is a standard
Tcl result: \fBTCL_OK\fR means the expression was successfully
evaluated, and \fBTCL_ERROR\fR means that an error occurred while
evaluating the expression.
If \fBTCL_ERROR\fR is returned,
then a message describing the error
can be retrieved using \fBTcl_GetObjResult\fR.
If an error occurs while executing a Tcl command embedded in
the expression then that error will be returned.
.PP
If the expression is successfully evaluated, then its value is
returned in one of four forms, depending on which procedure
is invoked.
\fBTcl_ExprLongObj\fR stores an integer value at \fI*longPtr\fR.
If the expression's actual value is a floating-point number,
then it is truncated to an integer.
If the expression's actual value is a non-numeric string then
an error is returned.
.PP
\fBTcl_ExprDoubleObj\fR stores a floating-point value at \fI*doublePtr\fR.
If the expression's actual value is an integer, it is converted to
floating-point.
If the expression's actual value is a non-numeric string then
an error is returned.
.PP
\fBTcl_ExprBooleanObj\fR stores a 0/1 integer value at \fI*booleanPtr\fR.
If the expression's actual value is an integer or floating-point
number, then they store 0 at \fI*booleanPtr\fR if
the value was zero and 1 otherwise.
If the expression's actual value is a non-numeric string then
it must be one of the values accepted by \fBTcl_GetBoolean\fR
such as
.QW yes
or
.QW no ,
or else an error occurs.
.PP
If \fBTcl_ExprObj\fR successfully evaluates the expression,
it stores a pointer to the Tcl object
containing the expression's value at \fI*resultPtrPtr\fR.
In this case, the caller is responsible for calling
\fBTcl_DecrRefCount\fR to decrement the object's reference count
when it is finished with the object.

.SH "SEE ALSO"
Tcl_ExprLong, Tcl_ExprDouble, Tcl_ExprBoolean, Tcl_ExprString, Tcl_GetObjResult

.SH KEYWORDS
boolean, double, evaluate, expression, integer, object, string