为什么运算符`?:`没有优先级? [英] Why operator `?:` does not have priority?

问题描述

调试后，我发现三元运算符?:没有优先级.我的问题是为什么?
我有以下代码:

After debugging I found that ternary operator ?: does not have priority. My question is why?
I have the following code:

bool T = true;
cout << ((T == true) ? "true" : "false") << endl;
cout << (T == true) ? "true" : "false";

输出:

true
1

实时演示: http://ideone.com/Tkvt9q

推荐答案

条件运算符确实具有优先级(尽管由于其三进制性质而有些复杂)；但是优先级很低.由于它低于<< ，因此第二个解析为

The conditional operator does have a precedence (albeit slightly complicated by its ternary nature); but that precedence is very low. Since it's lower than <<, the second is parsed as

(cout << (T == true)) ? "true" : "false";

流式传输 T == true 的布尔值，然后求值(但忽略)表达式"true" .如果启用了明智的警告，大多数编译器都会给出警告.

streaming the boolean value of T == true, then evaluating (but ignoring) the expression "true". Most compilers will give a warning, if you enable a sensible set of warnings.

这里是对运算符优先级的引用，显示的<< 优先级(7)比?:(15):http://en.cppreference.com/w/cpp/language/operator_precedence

Here is a reference to the operator precedences, showing << with a higher precedence (7) than ?: (15): http://en.cppreference.com/w/cpp/language/operator_precedence

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