当函数缺少返回值时，编译器会生成警告但不会出错？

Question

Here is a c++ function:

int FuncWithoutReturn()
{
  int var = 10;
  ++var;
  // No return value here !!!
}

In MSVC, compiler generates error:

error C4716: 'FuncWithoutReturn' : must return a value.

But in XCode 5, the compiler just spits a warning:

Control reaches end of non-void function

In runtime if I am lucky, the app crashes. I know it is a stupid error but it would be good that the compiler yields an error in first place.

Just wondering anyone knows WHY XCode think it is a warning instead of an error.

Answer 1

You can use -Werror=return-type to make that warning and error, in my original comment I forgot that. You can see it live .

This is both an option in clang and gcc , as far as I understand XCode can use either one.

Falling off the end of value returning function is undefined behavior , we can see this by going to the draft C++ standard section 6.6.3 The return statement paragraph 2 which says:

[...]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.

Undefined Behavior does not require a diagnostic( warning or error ), although in many cases compilers will provide one.

Answer 2

You can enable it using -Werror=return-type

Just wondering anyone knows WHY XCode think it is a warning instead of an error.

Check your project's/target's/xcconfig's settings for "Mismatched Return Type" (aka GCC_WARN_ABOUT_RETURN_TYPE ).