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.

       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 an expression,  return-
       ing  the  result  in  one  of  four  different forms.  The
       expression is given by 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 com-
       mands) and to return error information.  Interp->result is
       assumed to be initialized in the standard fashion when any
       of the procedures 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
       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 *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  Tcl_ExprBoolean  stores  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  interp->result.   If  the  expression's
       actual value is an integer then Tcl_ExprString converts it
       to a string using sprintf with a ``%d'' converter.  If the
       expression's actual value is a floating-point number, then
       Tcl_ExprString calls Tcl_PrintDouble to convert  it  to  a
       string.

KEYWORDS

       boolean, double, evaluate, expression, integer, string