Volume 7A: XView Programming Manual

24

Error Recovery

This chapter addresses the general-usage Error Handling facilities that apply to all XView

packages. All XView packages, including extensions to existing packages or those packages

you write yourself, should address error handling to provide adequate feedback for the pro-

grammer.

There are two different types of errors addressed: XView errors and Xlib protocol errors.

The two are very different from one another; XView errors are generated by misusing the

XView Toolkit in some way, while Xlib protocol errors result from calling Xlib functions

incorrectly or using incorrect values to those functions. We’ll start with XView errors since,

as you may already know, it is easy to generate run-time errors when writing XView applica-

tions.

24.1 XView Errors

XView errors are caused by specifying invalid or unknown attributes, objects, or values.

Often, XView errors are generated by simply failing to terminate a list of values of attribute-

value pairs. Whatever the reason, for an error, the XView internals call the function

xv_error().

This function is the highest level interface into the XView error package. Like many of the

other XView functions, xv_error() takes a

NULL-terminated attribute-value list of param-

eters. These parameters, set by the calling function, describe the nature of the error encoun-

tered. xv_error() then calls either a programmer-supplied function or a default