XSetErrorHandler()XSetErrorHandler()NameXSetErrorHandler – set a fatal error event handler.
Synopsis
int (*XSetErrorHandler(handler))()
int (* handler)(Display *)
Arguments
handler The user-defined function to be called to handle error
events. If a NULL pointer, reinvoke the default handler,
which prints a message and exits.
Returns
The previous nonfatal error handler.
Description
The error handler function specified in handler will be called by Xlib
whenever an XError event is received. These are nonfatal conditions,
such as unexpected values for arguments, or a failure in server memory
allocation. It is acceptable for this procedure to return, though the
default handler simply prints a message and exits. However, the error
handler should NOT perform any operations (directly or indirectly) that
generate protocol requests or that look for input events.
In Release 4 and Release 5, XSetErrorHandler() returns a pointer to the
previous error handler.
The function is called with two arguments: the display variable and a
pointer to the XErrorEvent structure. Here is a trivial example of a
user-defined error handler:
int myhandler (display, myerr)
Display *display;
XErrorEvent *myerr;
{
char msg[80];
XGetErrorText(display, myerr->error_code, msg, 80);
fprintf(stderr, "Error code %s\n", msg);
}
This is how the example routine would be used in XSetErrorHandler():
XSetErrorHandler(myhandler);
Note that XSetErrorHandler() is one of the few routines that does not
require a display argument. The routine that calls the error handler
gets the display variable from the XErrorEvent structure.
The error handler is not called on BadName errors from OpenFont,
LookupColor, and AllocNamedColor protocol requests, or on BadFont
errors from a QueryFont protocol request. These errors are all indi‐
cated by Status return value of zero in the corresponding Xlib rou‐
tines, which must be caught and handled by the application.
Use XIOErrorHandler to provide a handler for I/O errors such as network
failures or server host crashes.
In the XErrorEvent structure shown below, the serial member is the num‐
ber of requests (starting from 1) sent over the network connection
since it was opened. It is the number that was the value of the
request sequence number immediately after the failing call was made.
The request_code member is a protocol representation of the name of the
procedure that failed and is defined in <X11/Xproto.h>.
For more information, see Volume One, Chapter 3, Basic Window Program.
Structures
typedef struct {
int type
Display *display; /* display the event was read from */
XID resourceid; /* resource ID */
unsigned long serial; /* serial number of failed request */
unsigned char error_code; /* error code of failed request */
unsigned char request_code; /* major opcode of failed request */
unsigned char minor_code; /* minor opcode of failed request */
} XErrorEvent;
See AlsoXDisplayName(), XGetErrorDatabaseText(), XGetErrorText(), XSetAfter‐
Function(), XSetIOErrorHandler(), XSynchronize().
Xlib - Error Handling XSetErrorHandler()
