大家好,又见面了,我是全栈君。
一个简单的程序引发了一块让人纠结的领域,也许强调编程规范的重要性也在这把。规范了就easy避免一些问题。
程序是这种
int Change(int& a) { a = 4; return a; } int main() { int a = 10; cout << Change(a) << a; }
In C-Free : the output : 4 4
In VS2008 : the output : 4 10
差别出来了,按我的理解,应该C-free输出的对,可是还是探究了下,下面是我别人给我的回复:
Simply put, there is no rule that guarantees that “4 4” is right. Same goes for “4 10”.
As others have mentioned in the comments you have a case of undefined behaviour here. Even if this would be defined behaviour, code like this is difficult to understand. So I recommend to do
cout << Change(a); cout << a;
or
int b = a; cout << Change(a); cout << b;
whatever you really want to do.
另外,找到了C++不确定行为的一片天,有兴趣的能够在这里继续探究非常多C++出现不确定行为的情况。
http://en.cppreference.com/w/cpp/language/eval_order
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