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.
Copyright © 1989-1993 The Regents of the University of California. Copyright © 1994-1997 Sun Microsystems, Inc. Copyright © 1995-1997 Roger E. Critchlow Jr.