C++, ternary operator and cout

问题

this code doesn't work

int main(){
cout << 5 ? (5 ? 0 : 2) : 5;
system("pause");
return 0;
}

this code works

int main(){
cout << (5 ? (5 ? 0 : 2) : 5);
system("pause");
return 0;
}

can't understand why?

回答1:

cout << 5 ? (5 ? 0 : 2) : 5;

is parsed as

(cout << 5) ? (5 ? 0 : 2) : 5;

回答2:

This is due to operator precedence rules.

<< has higher precedence than ?, so your first expression is parsed as:

(cout << 5) ? (5 ? 0 : 2) : 5;

Brackets are necessary in this case to get the parse you want.

来源：https://stackoverflow.com/questions/31183993/c-ternary-operator-and-cout