C ++结构字段的顺序在聚合初始化中是否重要

Question

Is the following code produce defined behavior or undefined behavior. I tried it on my VC++ and I got one thing, but I'm curious to see if that is just coincendence or if it is mandated by the c++ standard.

#include <iostream>
class TestClass {
public:
    char testChar;
    double testDouble;
    int testInt;
};

int main(int argc, char** argv) {
    TestClass s = {412.1, 52};
    std::cout << s.testChar + s.testDouble + s.testInt << std::endl;
}

Answer 1

The behavior is defined, but the result might not be what you expect.

The order of the fields is important. For aggregate initialization each value will initialize the next member in order of declaration, so in the code above, testChar will get the value static_cast<char>(412.1) , testDouble will get value 52 and testInt will get value 0 (the standard guarantees that all members for which no value is provided will be initialized to 0.