使用全局常量

标头可用于声明全局使用的只读资源，例如字符串表。

在一个单独的标题中声明它们，它们被任何想要使用它们的文件（翻译单元） 包括在内。使用相同的头来声明相关的枚举以识别所有字符串资源非常方便：

resources.h：

#ifndef RESOURCES_H
#define RESOURCES_H

typedef enum { /* Define a type describing the possible valid resource IDs. */
  RESOURCE_UNDEFINED = -1, /* To be used to initialise any EnumResourceID typed variable to be 
                              marked as "not in use", "not in list", "undefined", wtf.
                              Will say un-initialised on application level, not on language level. Initialised uninitialised, so to say ;-)
                              Its like NULL for pointers ;-)*/
  RESOURCE_UNKNOWN = 0,    /* To be used if the application uses some resource ID, 
                              for which we do not have a table entry defined, a fall back in 
                              case we _need_ to display something, but do not find anything 
                              appropriate. */

  /* The following identify the resources we have defined: */
  RESOURCE_OK,
  RESOURCE_CANCEL,
  RESOURCE_ABORT,
  /* Insert more here. */

  RESOURCE_MAX /* The maximum number of resources defined. */
} EnumResourceID;

extern const char * const resources[RESOURCE_MAX]; /* Declare, promise to anybody who includes 
                                      this, that at linkage-time this symbol will be around. 
                                      The 1st const guarantees the strings will not change, 
                                      the 2nd const guarantees the string-table entries 
                                      will never suddenly point somewhere else as set during 
                                      initialisation. */
#endif

要实际定义资源，创建一个相关的 .c 文件，这是另一个翻译单元，它保存在相关标题（.h）文件中声明的实际实例：

resources.c：

#include "resources.h" /* To make sure clashes between declaration and definition are
                          recognised by the compiler include the declaring header into
                          the implementing, defining translation unit (.c file).

/* Define the resources. Keep the promise made in resources.h. */
const char * const resources[RESOURCE_MAX] = {
  "<unknown>",
  "OK",
  "Cancel",
  "Abort"
};

使用它的程序可能如下所示：

main.c 中：

#include <stdlib.h> /* for EXIT_SUCCESS */
#include <stdio.h>

#include "resources.h"

int main(void)
{
  EnumResourceID resource_id = RESOURCE_UNDEFINED;

  while ((++resource_id) < RESOURCE_MAX)
  {
    printf("resource ID: %d, resource: '%s'\n", resource_id, resources[resource_id]);
  }

  return EXIT_SUCCESS;
}

使用 GCC 编译上面的三个文件，并将它们链接成程序文件 main，例如使用：

gcc -Wall -Wextra -pedantic -Wconversion -g  main.c resources.c -o main

（使用这些 -Wall -Wextra -pedantic -Wconversion 使编译器非常挑剔，所以在将代码发布到 SO 之前不会遗漏任何内容，会说世界，甚至值得将其部署到生产中）

运行创建的程序：

$ ./main

得到：

resource ID: 0, resource: '<unknown>'
resource ID: 1, resource: 'OK'
resource ID: 2, resource: 'Cancel'
resource ID: 3, resource: 'Abort'