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Some errors, such as a value out of range, might be the result of erroneous user input. If the input is interactive, the program can prompt the user for an acceptable value. With other errors, such as a resource allocation failure, the system may have little choice other than but to shut down.

\[[ISO/IEC PDTR 24772|AA. C References#ISO/IEC PDTR 24772]\] Section 6.47, "REU Termination strategy," says:

When a fault is detected, there are many ways in which a system can react. The quickest and most noticeable way is to fail hard, also known as fail fast or fail stop. The reaction to a detected fault is to immediately halt the system. Alternatively, the reaction to a detected fault could be to fail soft. The system would keep working with the faults present, but the performance of the system would be degraded. Systems used in a high availability environment such as telephone switching centers, e-commerce, etc. would likely use a fail soft approach. What is actually done in a fail soft approach can vary depending on whether the system is used for safety critical or security critical purposes. For fail safe systems, such as flight controllers, traffic signals, or medical monitoring systems, there would be no effort to meet normal operational requirements, but rather to limit the damage or danger caused by the fault. A system that fails securely, such as cryptologic systems, would maintain maximum security when a fault is detected, possibly through a denial of service.

and And also:

The reaction to a fault in a system can depend on the criticality of the part in which the fault originates. When a program consists of several tasks, the tasks each may be critical, or not. If a task is critical, it may or may not be restartable by the rest of the program. Ideally, a task which detects a fault within itself should be able to halt leaving its resources available for use by the rest of the program, halt clearing away its resources, or halt the entire program. The latency of any such communication, and whether other tasks can ignore such a communication, should be clearly specified. Having inconsistent reactions to a fault, such as the fault reaction to a crypto fault, can potentially be a vulnerability.

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registers the turn_gizmo_off() function so that a subsequent call to exit() will invoke turn_gizmo_off() as it terminates the program. According to C99 , requires that atexit() can register up to at least 32 functions.

Functions registered by the atexit() is only function are called by exit() or upon normal completion of main().

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int main(int argc, char **argv) {
  /* ... */
  if (/* something really bad happened */) {
    return EXIT_FAILURE;
  }
  /* ... */
  return EXIT_SUCCESS;
}

C99, Section 5.1.2.2.3, has this to say about returning from {{main()}} \[[ISO/IEC 9899:1999|AA. C References#ISO/IEC 9899-1999]\]:

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void _start(void) {
  /* ... */
  exit(main(argc, argv));
}

However, making it out of exiting from main is conditional on correctly handling all errors in a way that does not force premature termination (see ERR00-C. Adopt and implement a consistent and comprehensive error-handling policy and ERR05-C. Application-independent code should provide error detection without dictating error handling).

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Whether open streams with unwritten buffered data are flushed, open streams are closed, or temporary files are removed is implementation-defined. Functions registered by atexit() are not executed (see ERR06-C. Understand the termination behavior of assert() and abort()).

Summary

The table below summarizes the exit behavior of the program termination functions.

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#include <stdlib.h>
#include <stdio.h>

int write_data(void) {
  const char *filename = "hello.txt";
  FILE *f = fopen(filename, "w");
  if (f == NULL) {
    /* handleHandle error */
  }
  fprintf(f, "Hello, World\n");
  /* ... */
  abort(); /* oops! data might not get written! */
  /* ... */
  return 0;
}

int main(void) {
  write_data();
  return 0;
}

...

#include <stdlib.h>
#include <stdio.h>

int write_data(void) {
  const char *filename = "hello.txt";
  FILE *f = fopen(filename, "w");
  if (f == NULL) {
    /* handleHandle error */
  }
  fprintf(f, "Hello, World\n");
  /* ... */
  exit(EXIT_FAILURE); /* writes data & closes f. */
  /* ... */
  return 0;
}

int main(void) {
  write_data();
  return 0;
}

While this particular example benefits from calling exit() over abort(), there will be situations where abort() is the better choice. Usually this will occur if one occurs when a programmer does not want need to close any file descriptors or call any handlers registered with atexit(), for instance, if the speed of terminating the program is critical.

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