
Tcl_ExprLong(3) Tcl Library Procedures Tcl_ExprLong(3)
_________________________________________________________________________________________________
NAME
Tcl_ExprLong, Tcl_ExprDouble, Tcl_ExprBoolean, Tcl_ExprString  evaluate an expression
SYNOPSIS
#include <tcl.h>
int
Tcl_ExprLong(interp, expr, longPtr)
int
Tcl_ExprDouble(interp, expr, doublePtr)
int
Tcl_ExprBoolean(interp, expr, booleanPtr)
int
Tcl_ExprString(interp, expr)
ARGUMENTS
Tcl_Interp *interp (in) Interpreter in whose context to evaluate expr.
const char *expr (in) Expression to be evaluated.
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.
_________________________________________________________________
DESCRIPTION
These four procedures all evaluate the expression given by the expr 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 objectbased procedures Tcl_ExprLongObj, Tcl_ExprDoubleObj, Tcl_ExprBooleanObj, and
Tcl_ExprObj. Those objectbased procedures evaluate an expression held in a Tcl object
instead of a string. The object argument can retain an internal representation that is
more efficient to execute.
The interp argument refers to an interpreter used to evaluate 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 describing 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 floatingpoint number, then it is trun
cated to an integer. If the expression's actual value is a nonnumeric string then an
error is returned.
Tcl_ExprDouble stores a floatingpoint value at *doublePtr. If the expression's actual
value is an integer, it is converted to floatingpoint. If the expression's actual value
is a nonnumeric 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 floatingpoint number, then they store 0 at *booleanPtr if the
value was zero and 1 otherwise. If the expression's actual value is a nonnumeric 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.
SEE ALSO
Tcl_ExprLongObj, Tcl_ExprDoubleObj, Tcl_ExprBooleanObj, Tcl_ExprObj
KEYWORDS
boolean, double, evaluate, expression, integer, object, string
Tcl 7.0 Tcl_ExprLong(3) 
