## Tcl8.6.2/Tk8.6.2 Documentation > Tcl C API, version 8.6.2 > ExprLong

### Tcl/Tk Applications | Tcl Commands | Tk Commands | [incr Tcl] Package Commands | SQLite3 Package Commands | TDBC Package Commands | tdbc::mysql Package Commands | tdbc::odbc Package Commands | tdbc::postgres Package Commands | tdbc::sqlite3 Package Commands | Thread Package Commands | Tcl C API | Tk C API | [incr Tcl] Package C API | TDBC Package C API

  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
  DESCRIPTION
  SEE ALSO
  KEYWORDS

### 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 value-based procedures Tcl_ExprLongObj, Tcl_ExprDoubleObj, Tcl_ExprBooleanObj, and Tcl_ExprObj. Those value-based procedures evaluate an expression held in a Tcl value instead of a string. The value 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 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 stores 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 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, value, string
Copyright © 1989-1993 The Regents of the University of California. Copyright © 1994-1997 Sun Microsystems, Inc.