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• shipped with the compiler or operating system.
• from a third-party library.
• developed in-house.

When application-specific code detects an error, it can immediately respond on the spot with a specific action, as in

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One way to indicate errors is to return a value indicating success or errorsfailure. This compliant solution ensures each function returns a value of type errno_t, where 0 indicates that no error has occurred.

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• Wiki Markup
  Source and object code can significantly increase in size, perhaps by as much as 30 to 40 percent \[[Saks 07b|AA. C References#Saks 07b]\].

• All function return values must be checked (see MEM32-C. Detect and handle memory allocation errors, among many others).)
• Functions should not return other values if they return error indicators (see ERR02-C. Avoid in-band error indicators.)
• Any function that allocates resources must ensure they are freed in_cases where errors occur.

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Instead of encoding status indicators in the return value, each function can take a pointer as an argument, which is used to indicate errors. In the following example, each function uses a errno_t\ * argument to report errors.

const errno_t ESOMETHINGREALLYBAD = 1;

void g(errno_t * err) {
  if (err == NULL) {
    /* Handle null pointer */
  }
  /* ... */
  if (something_really_bad_happens) {
    *err = ESOMETHINGREALLYBAD;
  } else {
    /* ... */
    *err = 0;
  }
}

void f(errno_t * err) {
  if (err == NULL) {
    /* Handle null pointer */
  }
  g(err);
  if (*err == 0) {
    /* ... do the rest of f ... */
  }
  return 0;
}

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• Source code size is inflated, though not by as much as in other approaches.
• All error indicators must be checked after calling functions.
• Nesting of function calls that all use this mechanism is problematic.
• Any function that allocates resources must ensure they are freed in cases where errors occur.
• In general, combining registries of different sets of errors is difficult. For example, changing the above this compliant solution code to use errno is difficult and bug-prone because the programmer must be precisely aware of when C library functions set and clear errno and also must be aware of all valid errno values before adding new ones.
• There are major limitations on calling f() from other application-independent code. Because f() sets my_errno to 0, it may potentially be overwriting a nonzero error value set by another application-independent calling function.

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Risk

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Assessment

Lack of an error-detection mechanism prevents applications from knowing when an error has disrupted normal program behavior.

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