++i 和 i++ 有什么区别?

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在C中，使用++i和i++有什么区别，哪个应该用在for 循环?

In C, what is the difference between using ++i and i++, and which should be used in the incrementation block of a for loop?

推荐答案

• ++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.