Return an anonymous instance/value in functions in C++

Vote count:

0

I have questions about the return type of function in C++.

Why return pair<int, int>(1, 1); and return vector<int>(3, 3); work? Shouldn't I create an local instance var before hand and take it as the return value, just like the return a, because return int 1 doesn't work.

// ...

int fun1() {
    // return int 1;
    int a = 1;
    return a;
}

pair<int, int> fun2() {
    return pair<int, int>(1, 1);
}

vector<int> fun3() {
    return vector<int>(3, 3);
}

int main(){
    cout << fun1() << endl;
    cout << fun2().first << endl;
    cout << fun3()[1] << endl;

    return 0;
}

Is it such a style to return can only be applied on class instances with specific constructor? The example below can work. I'm looking for confirmation, thanks at advance!

class A {
public:
    int a;
    A(int a_) : a(a_) {};
};

A fun4() {
    return A(1);
}

Code sample tested in:

Apple LLVM version 6.0 (clang-600.0.56) (based on LLVM 3.5svn) Target: x86_64-apple-darwin14.0.0 Thread model: posix

asked 45 secs ago

Jan Fan

3

Return an anonymous instance/value in functions in C++