在 MS Visual C++ 中启用 VLA(可变长度数组)? [英] Enabling VLAs (variable length arrays) in MS Visual C++?

问题描述

如何启用 VLA、C99 中定义的可变长度数组、MS Visual C++ 或根本不可能的使用?

How can I enable the use of VLAs, variable length arrays as defined in C99, in MS Visual C++ or that is not possible at all?

是的，我知道 C++ 标准基于 C89，并且 VLA 在 C89 标准中不可用，因此在 C++ 中不可用，但 MSVC++ 也应该是 C 编译器，一种可以打开的行为使用/TC 编译器参数(Compile as C Code (/TC)).但是这样做似乎并没有启用 VLA，并且编译过程在构建为 C++ 时失败并出现相同的错误(Compile as C++ Code (/TP)).也许 MSVC++ C 编译器仅符合 C89，或者我遗漏了一些东西(一些特殊的构造或编译指示/定义)?

Yes I know that the C++ standard is based on C89 and that VLAs are not available in C89 standard and thus aren't available in C++, but MSVC++ is supposed to be a C compiler also, a behavior that can be switched on using the /TC compiler parameter (Compile as C Code (/TC)). But doing so does not seem to enable VLAs and the compiling process fails with the same errors when building as C++ (Compile as C++ Code (/TP)). Maybe MSVC++ C compiler is C89 compliant only or I am missing something (some special construct or pragma/define)?

代码示例:

#include <stdlib.h>

int main(int argc, char **argv)
{
  char pc[argc+5];

  /* do something useful with pc */

  return EXIT_SUCCESS;
}

编译错误:

错误 C2057:预期的常量表达式

error C2057: expected constant expression

错误 C2466:无法分配大小为 0 的常量

error C2466: cannot allocate an array of constant size 0

错误 C2133:'pc':未知大小

error C2133: 'pc' : unknown size

推荐答案

MSVC 不是 C99 编译器，不支持变长数组.

MSVC is not a C99 compiler, and does not support variable length arrays.

在 https://docs.microsoft.com/en-us/cpp/c-language/ansi-conformance MSVC 被记录为符合 C90.

At https://docs.microsoft.com/en-us/cpp/c-language/ansi-conformance MSVC is documented as conforming to C90.

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