NAME
Tcl_ExprLong, Tcl_ExprDouble, Tcl_ExprBoolean,
Tcl_ExprString - evaluate an expression
SYNOPSIS
#include <tcl.h>
int
Tcl_ExprLong(interp, string, longPtr)
int
Tcl_ExprDouble(interp, string, doublePtr)
int
Tcl_ExprBoolean(interp, string, booleanPtr)
int
Tcl_ExprString(interp, string)
ARGUMENTS
Tcl_Interp *interp (in) Interpreter in whose
context to evaluate
string or objPtr.
char *string (in) Expression to be
evaluated. Must be
in writable memory
(the expression
parser makes tempo
rary modifications to
the string during
parsing, which it
undoes before return
ing).
long *longPtr (out) Pointer to location
in which to store the
integer value of the
expression.
int *doublePtr (out) Pointer to location
in which to store the
floating-point value
of the expression.
int *booleanPtr (out) Pointer to location
in which to store the
0/1 boolean value of
the expression.
_________________________________________________________________
These four procedures all evaluate the expression given by
the string argument and return the result in one of four
different forms. The expression can have any of the forms
accepted by the expr command. Note that these procedures
have been largely replaced by the object-based procedures
Tcl_ExprLongObj, Tcl_ExprDoubleObj, Tcl_ExprBooleanObj,
and Tcl_ExprStringObj. Those object-based procedures
evaluate an expression held in a Tcl object instead of a
string. The object argument can retain an internal repre
sentation that is more efficient to execute.
The interp argument refers to an interpreter used to eval
uate the expression (e.g. for variables and nested Tcl
commands) and to return error information.
For all of these procedures the return value is a standard
Tcl result: TCL_OK means the expression was successfully
evaluated, and TCL_ERROR means that an error occurred
while evaluating the expression. If TCL_ERROR is returned
then the interpreter's result will hold a message describ
ing the error. If an error occurs while executing a Tcl
command embedded in the expression then that error will be
returned.
If the expression is successfully evaluated, then its
value is returned in one of four forms, depending on which
procedure is invoked. Tcl_ExprLong stores an integer
value at *longPtr. 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.
Tcl_ExprDouble stores a floating-point value at *dou
blePtr. 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.
Tcl_ExprBoolean stores a 0/1 integer value at *booleanPtr.
If the expression's actual value is an integer or float
ing-point number, then they store 0 at *booleanPtr 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 Tcl_GetBoolean such as ``yes''
or ``no'', or else an error occurs.
Tcl_ExprString returns the value of the expression as a
string stored in the interpreter's result. If the expres
sion's actual value is an integer then Tcl_ExprString con
verts it to a string using sprintf with a ``%d'' con
verter. If the expression's actual value is a floating-
point number, then Tcl_ExprString calls Tcl_PrintDouble to
convert it to a string.
Tcl_ExprLongObj, Tcl_ExprDoubleObj, Tcl_ExprBooleanObj,
Tcl_ExprObj
KEYWORDS
boolean, double, evaluate, expression, integer, object,
string
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