Handling error conditions, exceptions, and signals

This topic discusses how to handle error conditions, exceptions, and signals with z/OS® XL C/C++. It describes how to establish, enable and raise a signal, and provides a list of signals supported by z/OS XL C/C++.

In 31-bit applications, there are two basic ways to handle program checks and ABENDs:

POSIX or ANSI signals (SIGABND, SIGFPE, SIGILL, SIGSEGV)
User condition handlers registered using CEEHDLR interface or the USRHDLR runtime option.

In 31-bit applications, z/OS Language Environment® uses a stack-based model to handle error conditions. This environment establishes a last-in, first-out (LIFO) queue of 0 or more user condition handlers for each stack frame. The z/OS Language Environment condition handler calls the user condition handler at each stack frame to handle error conditions when they are detected. For more information about the callable services in z/OS Language Environment, refer to Handling signals using Language Environment callable services.

In AMODE 64 applications, user condition handlers are not available. The basic ways to handle program checks and ABENDs in AMODE 64 applications are:

POSIX or ANSI signals (SIGABND, SIGFPE, SIGILL, SIGSEGV)
Exception handlers registered using the __set_exception_handler() C runtime library function. See AMODE 64 exception handlers for more information.

The C error handling approach using signals is supported in a z/OS XL C++ program, but there are some restrictions (refer to Handling C software exceptions under C++). See Signal handlers for more information.

C++ exception handling is supported in all z/OS environments that are supported by C++ (including CICS and IMS); you must run your application with the TRAP(ON) runtime option. To turn off C++ exception handling, use the compiler option NOEXH. For more information on this compiler option, see z/OS XL C/C++ User's Guide.

Note: If C++ exception handling is turned off you will get code which runs faster but is not ANSI conformant.

This topic also describes some aspects of C++ object-oriented exception handling. The object-oriented approach uses the try, throw, and catch mechanism. Refer to z/OS XL C/C++ Language Reference for a complete description. Some library functions (abort(), atexit(), exit(), setjmp() and longjmp()) are affected by C++ exception handling; refer to z/OS XL C/C++ Runtime Library Reference for more information.