Here's some example code:

#include <iostream>
 
using namespace std;
 
struct number { float x; };
 
number test_func(void) { static number v; return v; }
 
int main()
{
    const number one = { 1.0f };

    test_func() = one;
    test_func().x += 1.0f;
    
    cout << test_func().x << endl;
    
    return 0;
}

Mini quiz:

1. Without using a compiler look at the code. Would you expect any warnings or errors from the compiler? Why?

2. What would you expect the output to be if it compiled?

3. Now compare your results to what actually happens when you compile it. Is it what you expected?

your static is returned as a copy...

I know. That's why the results are interesting. Try it on a few compilers ;)

[spoiler]

As you've hopefully found out by now on some compilers the code doesn't produce a single error or warning. This is the result from Clang:

test.cpp:14:19: error: expression is not assignable
test_func().x += 1.0f;
~~~~~~~~~~~~~ ^

1 error generated.

I was expecting at least a warning from most compilers - the code is clearly not sensible. Clang didn't even pick up the other line of code that is equally bad...
[/spoiler]

Good to know that there's yet another instance where Clang points out non sensical code. I'm not sure it's correct though, but too lazy to check it... :)

Clang didn't even pick up the other line of code that is equally bad...

1. Without using a compiler look at the code. Would you expect any warnings or errors from the compiler? Why?

2. What would you expect the output to be if it compiled?

3. Now compare your results to what actually happens when you compile it. Is it what you expected?

const int &refToTemp = 357;

//Only makes a copy if 'condition' is false.
const std::string &myString = ( ...condition... ? this->memberString : this->GetCopyOfSubStr_ReturnByValue());
this->UseString(myString);

Also, test_func(void) should be test_func(), no need for the 'void' there.

Undefined gibberish value - whatever 'static number v' initially resolves to, because it has never been assigned anything.