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If control reaches the closing curly brace (}) of a non-void nonvoid function without evaluating a return statement, using the return value of the function call causes undefined behavior. See undefined behavior 88 in Annex J, subclause J .2 of the C Standard [ISO/IEC 9899:2011].

This rule is related to MSC01-C. Strive for logical completeness because both practices are intended to ensure that programs properly handle all possible conditions.

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int getlen(const int *input, size_t maxlen, int delim, size
           size_t *result) {
  for (size_t i = 0; i < maxlen; ++i) {
    if (input[i] == delim) {
      if (result != NULL) {
        *result = i;
      }
      return 0;
    }
  }
  return -1;
}


void func(int userdata) {
  size_t i;
  int data[] = {1, 1, 1};
  if (getlen(data, sizeof(data), 0, &i) != 0) {
    /* Handle error. */
  } else {
    data[i] = userdata;
  }
}

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MSC37-EX1: According to the C standardStandard, subclause 5.1.2.2.3, paragraph 1 [ISO/IEC 9899:2011], 

Reaching ...; reaching the } that terminates the main function returns a value of 0.

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Using the return value from a non-void nonvoid function where control reaches the end of the function can lead to a buffer overflow vulnerability as well as other unexpected program behaviors.

Related Vulnerabilities

Search for vulnerabilities resulting from the violation of this rule on the CERT website.

Bibliography

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