HP OpenVMS Systems Documentation

HP C
Run-Time Library Reference Manual for OpenVMS Systems

Table 4-1 lists and describes all the error- and signal-handling functions found in the HP C Run-Time Library (RTL). For more detailed information on each function, see the Reference Section.

When an error occurs during a call to any of the HP C RTL functions, the function returns an unsuccessful status. Many RTL routines also set the external variable errno to a value that indicates the reason for the failure. You should always check the return value for an error situation.

The <errno.h> header file declares errno and symbolically defines the possible error codes. By including the <errno.h> header file in your program, you can check for specific error codes after a HP C RTL function call.

At program startup, the value of errno is 0. The value of errno can be set to a nonzero value by many HP C RTL functions. It is not reset to 0 by any HP C RTL function, so it is only valid to use errno after a HP C RTL function call has been made and a failure status returned. Table 4-2 lists the symbolic values that may be assigned to errno by the HP C RTL.

You can translate the error codes to a message, similar to that found in UNIX systems, by using the perror or strerror function. If errno is set to EVMSERR, perror cannot translate the error code and prints the following message, followed by the OpenVMS error message associated with the value:

%s:nontranslatable vms error code: xxxxxx vms message:

In the message, %s is the string you supply to perror ; xxxxxx is the OpenVMS condition value.

If errno is set to EVMSERR, then the OpenVMS condition value is available in the vaxc$errno variable declared in the <errno.h> header file. The vaxc$errno variable is guaranteed to have a valid value only if errno is set to EVMSERR; if errno is set to a value other than EVMSERR, the value of vaxc$errno is undefined.

See the strerror function in the Reference Section for another way to translate error codes.

4.2 Signal Handling

A signal is a form of software interrupt to the normal execution of a user process. Signals occur as a result of a variety of events, including any of the following:

• Typing Ctrl/C at a terminal
• Certain programming errors
• A call to the gsignal or raise function
• A wake-up action

Both OpenVMS and UNIX systems provide signal-handling mechanisms that behave differently but use similar terminology. With the HP C RTL, you can program using either signal-handling mechanism. Before describing the signal-handling routines, some terminology must be established.

The UNIX term for a software interrupt is signal. A routine called by the UNIX system to process a signal is termed a signal handler.

A software interrupt on an OpenVMS system is referred to as a signal, condition, or exception. A routine called by the OpenVMS system to process software interrupts is termed a signal handler, condition handler, or exception handler.

To prevent confusion, the terms signal and signal handler in this manual refer to UNIX interrupts and interrupt processing routines, while the terms exception and exception handler refer to OpenVMS interrupts and interrupt processing routines.

4.2.2 UNIX Signals and the HP C RTL

Signals are represented by mnemonics defined in the <signal.h> header file. Table 4-3 lists the supported signal mnemonics and the corresponding event that causes each signal to be generated on the OpenVMS operating system.

By default, when a signal (except for SIGCHLD) occurs, the process is terminated. However, you can choose to have the signal ignored by using one of the following functions:

sigaction
signal
sigvec
ssignal

You can have the signal blocked by using one of the following functions:

sigblock
sigsetmask
sigprocmask
sigsuspend
sigpause

Table 4-3 indicates those signals that cannot be ignored or blocked.

You can also establish a signal handler to catch and process a signal by using one of the following functions:

sigaction
signal
sigvec
ssignal

Unless noted in Table 4-3, each signal can be reset. A signal is reset if the signal handler function calls signal or ssignal to re-establish itself to catch the signal. Example 4-1 shows how to establish a signal handler and reset the signal.

The calling interface to a signal handler is:

Where sigint is the signal number of the raised signal that caused this handler to be called.