Tcl_ExprBoolean (3)  Linux Manuals
Tcl_ExprBoolean: evaluate an expression
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 floatingpoint 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 truncated 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.
KEYWORDS
boolean, double, evaluate, expression, integer, object, string