如何在C中的for（;;）循环中声明几个变量？ [英] How do I declare several variables in a for (;;) loop in C?

问题描述

我以为可以在 for 循环中声明几个变量：

I thought one could declare several variables in a for loop:

for (int i = 0, char* ptr = bam; i < 10; i++) { ... }

但是我刚刚发现这是不可能的。 GCC给出以下错误：

But I just found out that this is not possible. GCC gives the following error:

错误： char之前的预期unqualified-id

error: expected unqualified-id before 'char'

您确实不能在 for 循环中声明不同类型的变量吗？

Is it really true that you can't declare variables of different types in a for loop?

推荐答案

您可以（但通常不应该）使用本地结构类型。

You can (but generally shouldn't) use a local struct type.

for ( struct { int i; char* ptr; } loopy = { 0, bam };
      loopy.i < 10 && * loopy.ptr != 0;
      ++ loopy.i, ++ loopy.ptr )
    { ... }

---

自C ++ 11起，只要它们不依赖局部变量，就可以更优雅地初始化各个部分：

---

Since C++11, you can initialize the individual parts more elegantly, as long as they don't depend on a local variable:

for ( struct { int i = 0; std::string status; } loop;
      loop.status != "done"; ++ loop.i )
    { ... }

这几乎足以真正使用。

C ++ 17解决了 结构化绑定 ：

C++17 addresses the problem with structured bindings:

for ( auto [ i, status ] = std::tuple{ 0, ""s }; status != "done"; ++ i )

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