实施例

file1.c

    const unsigned char data1[] =
    {
    0x65, 0xF0, 0xA8, 0x5F, 0x5F,
    0x5F, 0x5F, 0x31, 0x32, 0x2E,
    0x31, 0xF1, 0x63, 0x4D, 0x43, 
    0x52, 0x45, 0x41, 0x54, 0x45,
    0x44, 0x20, 0x42, 0x59, 0x3A,
    0x20, 0x69, 0x73, 0x70, 0x56, 
// ...
    };
    const unsigned int data1_size =
        sizeof(data1) / sizeof(data1[0]);
    const unsigned int data1_version = 1;

file2.c

    const unsigned char data2[] =
    {
    0x20, 0x44, 0x61, 0x74, 0x61,
    0x20, 0x52, 0x6F, 0x77, 0x20,
    0x3D, 0x20, 0x34, 0x38, 0x12, 
//...
    };
    const unsigned int data2_size =
        sizeof(data2) / sizeof(data2[0]);
    const unsigned int data2_version = 1;

的main.c

struct Data_Info
{
  unsigned char * data_ptr;
  unsigned int    data_size;
  unsigned int    data_version;
};

extern const unsigned char data1[];
extern const unsigned int  data1_size;
extern const unsigned int  data1_version;

extern const unsigned char data2[];
extern const unsigned int  data2_size;
extern const unsigned int  data2_version;

static struct Data_Info  Data_Info_Table[] =
{
  // How to set this up??
  // The compiler wants constant expressions here,
  //    and the extern is not considered a constant expression
  // This is what I tried:
  { data1, data1_size, data1_version},
  { data2, data2_size, data2_version},
};

int main(void)
{
  return 0;
}

我正在使用Green Hills Compiler，4.2.3。确切的错误消息：

error #28, expression must have a constant value.

见我之前的帖子：
C: External const ints in a array of const struct

注意：包含C ++标记，因为这也适用于C ++

Answer 1

你尝试过吗？（其中X为0或1。）

struct Data_Info    
{    
  unsigned char const * data_ptr;    
  unsigned int    data_size;    
  unsigned int    data_version;    
};

fileX.h

extern const struct Data_Info data_infoX;

fileX.c

const struct Data_Info data_infoX = { dataX, dataX_size, dataX_version };

的main.c

const struct Data_Info const * Data_Info_Table[] = 
{ 
  &data_info1,
  &data_info2
};

Answer 2

问题是编译器不知道要放入该字段的data_size和data_version成员的值。有几种方法可以解决这个问题，而不用太多大惊小怪。

方法1：

#include "data1.c"
#include "data2.c"

...
static struct Data_Info  Data_Info_Table[] =
{
  { data1, sizeof(data1), 1},
  { data2, sizeof(data2), 1},
};

方法2：

struct Data_Info
{
  unsigned char * data_ptr;
  unsigned int *  data_size;
  unsigned int *  data_version;
};

...

static struct Data_Info  Data_Info_Table[] =
{
  { data1, &data1_size, &data1_version},
  { data2, &data2_size, &data2_version},
};

jyoung已经证明，第三种方法是在单独的数据文件中分配成员，并将其地址包含在Data_Info_Table中。

Answer 3

定义常量时，请使用extern关键字。

Answer 4

我不是那么多C专家，但是不同翻译单元的初始化顺序很可能是未定义的（我知道它在C ++中是未定义的，如果C中的行为不同，那将是一个巨大的兼容性中断），所以即使编译器允许它也是危险的。

现在，添加C ++标签很可能不会有多大帮助，因为AFAIK不仅依赖于语言，还依赖于语言的特定版本：C89 / C99。在C ++中，如果将初始化移动到头文件中的常量声明，它就可以工作。再说一次，我不是C专家。

如何使用extern值创建表（数组）？

实施例

4 个答案: