archie/tcl7.6/doc/ExprLong.3

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'\" Copyright (c) 1989-1993 The Regents of the University of California.
'\" Copyright (c) 1994-1996 Sun Microsystems, Inc.
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'\" SCCS: @(#) ExprLong.3 1.18 96/08/26 12:59:46
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.so man.macros
.TH Tcl_ExprLong 3 7.0 Tcl "Tcl Library Procedures"
.BS
.SH NAME
Tcl_ExprLong, Tcl_ExprDouble, Tcl_ExprBoolean, Tcl_ExprString \- evaluate an expression
.SH SYNOPSIS
.nf
\fB#include <tcl.h>\fR
.sp
int
\fBTcl_ExprLong\fR(\fIinterp, string, longPtr\fR)
.sp
int
\fBTcl_ExprDouble\fR(\fIinterp, string, doublePtr\fR)
.sp
int
\fBTcl_ExprBoolean\fR(\fIinterp, string, booleanPtr\fR)
.sp
int
\fBTcl_ExprString\fR(\fIinterp, string\fR)
.SH ARGUMENTS
.AS Tcl_Interp *booleanPtr
.AP Tcl_Interp *interp in
Interpreter in whose context to evaluate \fIstring\fR.
.AP char *string in
Expression to be evaluated.  Must be in writable memory (the expression
parser makes temporary modifications to the string during parsing, which
it undoes before returning).
.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.
.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 \fIstring\fR argument, and it
can have any of the forms accepted by the \fBexpr\fR command.
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.  \fIInterp->result\fR
is assumed to be initialized in the standard fashion when any
of the procedures are invoked.
.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
\fIinterp->result\fR will hold a message describing the error.
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_ExprLong\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_ExprDouble\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_ExprBoolean\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 \fBTcl_ExprBoolean\fR stores 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 ``yes'' or ``no'', or else an error occurs.
.PP
\fBTcl_ExprString\fR returns the value of the expression as a
string stored in \fIinterp->result\fR.
If the expression's actual value is an integer
then \fBTcl_ExprString\fR converts it to a string using \fBsprintf\fR
with a ``%d'' converter.
If the expression's actual value is a floating-point
number, then \fBTcl_ExprString\fR calls \fBTcl_PrintDouble\fR
to convert it to a string.

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