除了递增语句，如何使for循环变量const? [英] How to make a for loop variable const with the exception of the increment statement?

问题描述

考虑循环标准:

for (int i = 0; i < 10; ++i) 
{
   // do something with i
}

我想防止在for循环的主体中修改变量i.

I want to prevent the variable i from being modified in the body of the for loop.

但是，我不能将i声明为const，因为这会使增量语句无效.有没有办法在增量语句之外使i成为const变量?

However, I cannot declare i as const as this makes the increment statement invalid. Is there a way to make i a const variable outside of the increment statement?

推荐答案

从c ++ 20开始，您可以使用 ranges :: views :: iota 像这样:

From c++20, you can use ranges::views::iota like this:

for (int const i : std::views::iota(0, 10))
{
   std::cout << i << " ";  // ok
   i = 42;                 // error
}

这是演示.

从c ++ 11开始，您还可以使用以下技术，该技术使用IIILE(立即调用的内联lambda表达式):

From c++11, you can also use the following technique, which uses an IIILE (immediately invoked inline lambda expression):

int x = 0;
for (int i = 0; i < 10; ++i) [&,i] {
    std::cout << i << " ";  // ok, i is readable
    i = 42;                 // error, i is captured by non-mutable copy
    x++;                    // ok, x is captured by mutable reference
}();     // IIILE

这是演示.

请注意，[&,i]表示i是由非可变副本捕获的，其他所有内容都是由可变引用捕获的.循环末尾的();只是意味着立即调用lambda.

Note that [&,i] means that i is captured by non-mutable copy, and everything else is captured by mutable reference. The (); at the end of the loop simply means that the lambda is invoked immediately.

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