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).
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; } } |
In this compliant solution, all code paths now return a value.
int absolute_value(int a) { if (a < 0) { return -a; } return a; } |
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 (...) { } |
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; } |
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"); } |
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 |
Tool | Version | Checker | Description |
---|---|---|---|
Astrée | return-implicit | Fully checked | |
Axivion Bauhaus Suite | CertC++-MSC52 | ||
Clang | -Wreturn-type | Does not catch all instances of this rule, such as function-try-blocks | |
CodeSonar | LANG.STRUCT.MRS | Missing return statement Non-void noreturn, | |
Helix QAC | DF2888 | ||
Klocwork | FUNCRET.GEN FUNCRET.IMPLICIT | ||
LDRA tool suite | 2 D, 36 S | Fully implemented | |
Parasoft C/C++test | CERT_CPP-MSC52-a | All exit paths from a function, except main(), with non-void return type shall have an explicit return statement with an expression | |
Polyspace Bug Finder | CERT C++: MSC52-CPP | Checks for missing return statements (rule partially covered) | |
SonarQube C/C++ Plugin | S935 | ||
PVS-Studio | V591 | ||
RuleChecker | return-implicit | Fully checked |
Search for vulnerabilities resulting from the violation of this rule on the CERT website.
[ISO/IEC 14882-2014] | Subclause 3.6.1, "Main Function" |