Tcl_ExprString man page on aLinux

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Tcl_ExprLong(3)		    Tcl Library Procedures	       Tcl_ExprLong(3)

______________________________________________________________________________

NAME
       Tcl_ExprLong,  Tcl_ExprDouble, Tcl_ExprBoolean, Tcl_ExprString - evalu‐
       ate 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  object-
       based	procedures   Tcl_ExprLongObj,	Tcl_ExprDoubleObj,   Tcl_Expr‐
       BooleanObj, and Tcl_ExprObj.  Those object-based procedures evaluate an
       expression  held in a Tcl object instead of a string.  The object argu‐
       ment 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, object, string

Tcl				      7.0		       Tcl_ExprLong(3)
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