Tcl - Tcl_ExprLong (3)

Tcl Library Procedures

NAME

Tcl_ExprLong, Tcl_ExprDouble, Tcl_ExprBoolean, Tcl_ExprBooleanObj, Tcl_ExprString, Tcl_ExprStringObj - 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_ExprBooleanObj(interp, objPtr, ptr)

int
Tcl_ExprString(interp, string)

int
Tcl_ExprStringObj(interp, objPtr)

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 temporary modifications to the string during parsing, which it undoes before returning).
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.
Tcl_Obj *objPtr (in): Pointer to an object containing the expression to evaluate.

DESCRIPTION

These six procedures all evaluate an expression, returning the result in one of four different forms. The expression is given by either the objPtr or the string argument, and it can have any of the forms accepted by the expr command. 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 procedures except Tcl_ExprBooleanObj and Tcl_ExprStringObj, interp->result is assumed to be initialized in the standard fashion when they are invoked.

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 by Tcl_ExprBooleanObj or Tcl_ExprStringObj, then interp->objResult will hold a message describing the error. This message object can be retrieved using Tcl_GetObjResult. If TCL_ERROR is returned by the other procedures then interp->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 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 *doublePtr. 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 and Tcl_ExprBooleanObj store a 0/1 integer value at *booleanPtr. If the expression's actual value is an integer or floating-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 and Tcl_ExprStringObj return the value of the expression as a string stored in either interp->result or interp->objResult. If the expression's actual value is an integer then they convert it to a string using sprintf with a ``%d'' converter. If the expression's actual value is a floating-point number, then they call Tcl_PrintDouble to convert it to a string.

KEYWORDS

boolean, double, evaluate, expression, integer, object, string

Last change: 7.0