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

问题描述

我认为可以在 for 循环中声明多个变量:

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' 之前的预期未限定 id

error: expected unqualified-id before 'char'

在 for 循环中不能声明不同类型的变量是真的吗?

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 )
    { ... }

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从 C++11 开始，您可以更优雅地初始化各个部分，只要它们不依赖于局部变量:

---

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 )
    { ... }

这几乎是可读的，可以真正使用.

This is just almost readable enough to really use.

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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