++i 和 i++ 有什么区别?

++i 将增加 i 的值，然后返回增加的值.

• ++i will increment the value of i, and then return the incremented value.

   i = 1;
   j = ++i;
   (i is 2, j is 2)
  

• i++ 将增加 i 的值，但返回 i 增加前的原始值.

• i++ will increment the value of i, but return the original value that i held before being incremented.

   i = 1;
   j = i++;
   (i is 2, j is 1)
  

对于 for 循环，两者都可以.++i 似乎更常见，也许是因为 K&R.

For a for loop, either works. ++i seems more common, perhaps because that is what is used in K&R.

在任何情况下，遵循首选 ++i 而不是 i++"的准则，你就不会出错.

In any case, follow the guideline "prefer ++i over i++" and you won't go wrong.

有一些关于 ++i 和 i++ 的效率的评论.在任何非学生项目编译器中，不会有性能差异.您可以通过查看生成的代码来验证这一点，它们将是相同的.

There's a couple of comments regarding the efficiency of ++i and i++. In any non-student-project compiler, there will be no performance difference. You can verify this by looking at the generated code, which will be identical.

效率问题很有趣……这是我试图回答的问题:C 中的 i++ 和 ++i 之间有性能差异吗?

The efficiency question is interesting... here's my attempt at an answer: Is there a performance difference between i++ and ++i in C?

正如 ​​@OnFreund 所指出的，C++ 对象是不同的，因为 operator++() 是一个函数，编译器不知道优化创建一个临时对象来保存中间值.

As @OnFreund notes, it's different for a C++ object, since operator++() is a function and the compiler can't know to optimize away the creation of a temporary object to hold the intermediate value.