c - extern const 数组声明/初始化错误(无效的初始化器/冲突类型)

Question

对于我正在从事的项目，我想要一个静态初始化的、不可变的全局数组——具体来说是一个数组，而不是一个枚举。据我所知，最好的方法是使用 extern const 数组。但是，当我尝试初始化和声明任何数组 foo 时，我收到两个不同但明显相关的编译器错误:

error: conflicting types for `foo'
error: invalid initializer

对于我的 .c 文件外部范围中的每次初始化，都会重复这些操作。前一个错误后面总是跟着一条注释:“前一个‘foo’的声明在这里”并指向头文件中数组的声明。

在以下示例中...

#ifndef __MWE__
#define __MWE__

extern const int foo[8];

#endif /* MWE */

#include "mwe.h"
const int foo[0] = 0;
const int foo[1] = 42;
const int foo[2] = 69;
const int foo[3] = 420;
const int foo[4] = 9001;


int main(int argc,char**argv){return 0;}

...我收到以下错误...

mwe.c:3:11: error: conflicting types for ‘foo’
 const int foo[0] = 0;
           ^~~
In file included from mwe.c:1:0:
mwe.h:4:18: note: previous declaration of ‘foo’ was here
 extern const int foo[5];
                  ^~~
mwe.c:3:20: error: invalid initializer
 const int foo[0] = 0;
                    ^
mwe.c:4:11: error: conflicting types for ‘foo’
 const int foo[1] = 42;
           ^~~
In file included from mwe.c:1:0:
mwe.h:4:18: note: previous declaration of ‘foo’ was here
 extern const int foo[5];
                  ^~~
mwe.c:4:20: error: invalid initializer
 const int foo[1] = 42;
                    ^~
mwe.c:5:11: error: conflicting types for ‘foo’
 const int foo[2] = 69;
           ^~~
In file included from mwe.c:1:0:
mwe.h:4:18: note: previous declaration of ‘foo’ was here
 extern const int foo[5];
                  ^~~
mwe.c:5:20: error: invalid initializer
 const int foo[2] = 69;
                    ^~
mwe.c:6:11: error: conflicting types for ‘foo’
 const int foo[3] = 420;
           ^~~
In file included from mwe.c:1:0:
mwe.h:4:18: note: previous declaration of ‘foo’ was here
 extern const int foo[5];
                  ^~~
mwe.c:6:20: error: invalid initializer
 const int foo[3] = 420;
                    ^~~
mwe.c:7:11: error: conflicting types for ‘foo’
 const int foo[4] = 9001;
           ^~~
In file included from mwe.c:1:0:
mwe.h:4:18: note: previous declaration of ‘foo’ was here
 extern const int foo[5];
                  ^~~
mwe.c:7:20: error: invalid initializer
 const int foo[4] = 9001;

声明和初始化 extern const 数组的正确方法是什么？这种方法无效的原因是什么？类型冲突在哪里？为什么整数文字对于整数数组的元素来说是无效的初始值设定项？

Answer 1

其中每一个:

const int foo[0] = 0;
const int foo[1] = 42;
const int foo[2] = 69;
const int foo[3] = 420;
const int foo[4] = 9001;

是名为 foo 的数组变量的单独定义，每个变量的大小不同。您还尝试使用单个值初始化这些数组。这就是您收到错误的原因。

如果你想初始化一个数组，你可以这样做:

const int foo[5] = { 0, 42, 69, 420, 9001 };

如果您需要根据枚举值初始化特定索引，可以使用指定的初始化器来执行此操作:

enum {
    E1, E2, E3, E4, E5
};
const int foo[5] = { 
    [E1] = 0, 
    [E2] = 42, 
    [E3] = 69, 
    [E4] = 420, 
    [E5] = 9001 
};