零长度数组调用memcmp触发array-bounds错误，如何修正代码？

原始代码 #

#include "memory.h"
#include "stdint.h"

#define MOLECULE_API_DECORATOR
MOLECULE_API_DECORATOR const uint8_t MolDefault_ByteOpt[0]      = {};

int main(int argc, char *argv[]) {
    uint32_t size = sizeof(MolDefault_ByteOpt);
    const uint8_t *expected = MolDefault_ByteOpt;
    const uint8_t *actual = NULL;
    if (memcmp(actual, expected, size) != 0){
        return 1;
    }
    return 0;
}

编译错误信息 #

使用gcc -Werror -Wall main.c编译时出现以下错误：

main.c: In function ‘main’:
main.c:8:5: error: offset ‘0’ outside bounds of constant string [-Werror=array-bounds]
    8 | int main(int argc, char *argv[]) {
      |     ^~~~
main.c:6:38: note: ‘MolDefault_ByteOpt’ declared here
    6 | MOLECULE_API_DECORATOR const uint8_t MolDefault_ByteOpt[0]      = {};
      |                                      ^~~~~~~~~~~~~~~~~~
main.c:10:31: error: offset ‘0’ outside bounds of constant string [-Werror=array-bounds]
   10 |     const uint8_t *expected = MolDefault_ByteOpt;
      |                               ^~~~~~~~~~~~~~~~~~
main.c:6:38: note: ‘MolDefault_ByteOpt’ declared here
    6 | MOLECULE_API_DECORATOR const uint8_t MolDefault_ByteOpt[0]      = {};
      |                                      ^~~~~~~~~~~~~~~~~~
main.c:8:5: error: offset ‘0’ outside bounds of constant string [-Werror=array-bounds]
    8 | int main(int argc, char *argv[]) {
      |     ^~~~
main.c:6:38: note: ‘MolDefault_ByteOpt’ declared here
    6 | MOLECULE_API_DECORATOR const uint8_t MolDefault_ByteOpt[0]      = {};
      |                                      ^~~~~~~~~~~~~~~~~~
cc1: all warnings being treated as errors

问题原因 #

零长度数组[0]属于GCC扩展特性，并非C标准的一部分。新版本GCC（如12.2.1）的-Wall会严格检测数组访问边界：零长度数组没有任何元素，尝试获取其地址或引用时，会触发array-bounds警告，而-Werror将警告转为错误导致编译失败。

修复方案 #

方案1：改用指针+显式长度定义 #

将零长度数组替换为指针和单独的长度常量，完全符合C标准，避免边界检测问题：

#include "memory.h"
#include "stdint.h"

#define MOLECULE_API_DECORATOR
MOLECULE_API_DECORATOR const uint8_t *const MolDefault_ByteOpt = NULL;
MOLECULE_API_DECORATOR const uint32_t MolDefault_ByteOpt_Size = 0;

int main(int argc, char *argv[]) {
    uint32_t size = MolDefault_ByteOpt_Size;
    const uint8_t *expected = MolDefault_ByteOpt;
    const uint8_t *actual = NULL;
    
    // 长度为0时无需执行memcmp，直接判定为相等
    if (size != 0 && memcmp(actual, expected, size) != 0) {
        return 1;
    }
    return 0;
}

方案2：调整数组定义并优化比较逻辑 #

如果需要保留数组形式，可改用未指定长度的空数组，并在比较时跳过长度为0的情况：

#include "memory.h"
#include "stdint.h"

#define MOLECULE_API_DECORATOR
MOLECULE_API_DECORATOR const uint8_t MolDefault_ByteOpt[] = {};

int main(int argc, char *argv[]) {
    uint32_t size = sizeof(MolDefault_ByteOpt);
    const uint8_t *expected = MolDefault_ByteOpt;
    const uint8_t *actual = NULL;
    
    // 长度为0时memcmp返回0，无需执行比较
    if (size != 0 && memcmp(actual, expected, size) != 0) {
        return 1;
    }
    return 0;
}

两种方案都能正常编译通过，且保留了原代码中对actual和expected的比较逻辑。

内容的提问来源于stack exchange，提问作者Eval EXEC