CertC++-MSC52

Value-returning functions must return a value from all exit paths

Required inputs: IR

The C++ Standard, [stmt.return], paragraph 2 [ ISO/IEC 14882-2014], states the following: 

Flowing off the end of a function is equivalent to a return with no value; this results in undefined behavior in a value-returning function.

A value-returning function must return a value from all code paths; otherwise, it will result in undefined behavior. This includes returning through less-common code paths, such as from a function-try-block, as explained in the C++ Standard, [except.handle], paragraph 15:

Flowing off the end of a function-try-block is equivalent to a return with no value; this results in undefined behavior in a value-returning function (6.6.3).

Noncompliant Code Example

In this noncompliant code example, the programmer forgot to return the input value for positive input, so not all code paths return a value.

int absolute_value(int a) {
  if (a < 0) {
    return -a;
  }
}
Compliant Solution

In this compliant solution, all code paths now return a value.

int absolute_value(int a) {
  if (a < 0) {
    return -a;
  }
  return a;
}
Noncompliant Code Example

In this noncompliant code example, the function-try-block handler does not return a value, resulting in  undefined behavior when an exception is thrown. 

#include <vector>

std::size_t f(std::vector<int> &v, std::size_t s) try {
  v.resize(s);
  return s;
} catch (...) {
}
Compliant Solution

In this compliant solution, the exception handler of the function-try-block also returns a value. 

#include <vector>

std::size_t f(std::vector<int> &v, std::size_t s) try {
  v.resize(s);
  return s;
} catch (...) {
  return 0;
}
Exceptions

MSC54-CPP-EX1: Flowing off the end of the  main() function is equivalent to a  return 0; statement, according to the C++ Standard, [basic.start.main], paragraph 5 [ ISO/IEC 14882-2014].  Thus, flowing off the end of the  main() function does not result in  undefined behavior.

MSC54-CPP-EX2: It is permissible for a control path to not return a value if that code path is never expected to be taken and a function marked  [[noreturn]] is called as part of that code path or if an exception is thrown, as is illustrated in the following code example. 

#include <cstdlib>
#include <iostream>
[[noreturn]] void unreachable(const char *msg) {
  std::cout << "Unreachable code reached: " << msg << std::endl;
  std::exit(1);
}

enum E {
  One,
  Two,
  Three
};

int f(E e) {
  switch (e) {
  case One: return 1;
  case Two: return 2;
  case Three: return 3;
  }
  unreachable("Can never get here");
}
Risk Assessment

Failing to return a value from a code path in a value-returning function results in  undefined behavior that might be  exploited to cause data integrity violations.

Rule Severity Likelihood Remediation Cost Priority Level
MSC52-CPP Medium Probable Medium P8 L2
Bibliography
[ ISO/IEC 14882-2014] Subclause 3.6.1, "Main Function"
Subclause 6.6.3, "The return Statement"
Subclause 15.3, "Handling an Exception"
Excerpt from SEI CERT C++ Coding Standard [https://cmu-sei.github.io/secure-coding-standards/sei-cert-cpp-coding-standard/rules/miscellaneous-msc/msc52-cpp], Copyright (C) 1995-2026 Carnegie Mellon University. See section 9.4. "3rd-Party Licenses" in the documentation for full details.

Possible Messages

Key

Text

Severity

Disabled

lambda_return_missing_value

Return without value in non-void lambda expression

None

False

missing_return

Value-returning functions must return a value from all exit paths.

None

False

missing_return_in_lambda

Value-returning lambda expressions must return a value from all exit paths.

None

False

return_missing_value

Return without value in non-void function

None

False

Options

exclude_missing_return_for_main

exclude_missing_return_for_main : bool = False

If True, no message for a missing return in main() will be reported.