RETURN语句中的表达式将被执行吗？

Question

I have a problem,will expressions in RETURN statement be excuted?

int test()
{
    top=10;
    return top--;
}

My problem is,what's the value of top ,10 or 9? Anybody can help me?I'm just a beginner.

Answer 1

The return value of test() in this case will be 10; The decrement on the 'top' variable will occur after the function's return value has been returned.

So say you have top as a global

int top;

int test()
{
    top = 10;
    return top--;
}

int main()
{
    top = 0;

    int tmp = test();

    std::cout << "top " << top << " tmp " << tmp << std::endl; // top = 9, tmp = 10
    return 0;
}

Answer 2

The postfix increment and decrement operators will always be performed after the current value is used, so in the code shown in the question 10 will be returned. What the value of top is in the function afterwards doesn't matter, since the function will no longer be executing. If the compiler is smart enough, it might optimize away the actual decrement since it's "dead code".

Answer 3

top-- will decrement top and return the original, so test will return 10 . If top has local storage duration, theoretically it will have a value of 9 when the function returns, but that doesn't really mean anything as the function is over and the whole calculation will likely be optimized out anyway. If top has non-local storage then you can rely on it being 9 when the function exits.