全局变量的多重定义 [英] Multiple definition of a global variable

问题描述

可能重复:
常量变量在标题中不起作用

Possible Duplicate:
constant variables not working in header

在用于创建共享库的头文件中，具有以下内容:

In my header file which I use to create a shared object, I have the following:

#ifndef LIB_HECA_DEF_H_
#define LIB_HECA_DEF_H_

struct dsm_config {
    int auto_unmap;
    int enable_copy_on_access;
};

enum { NO_AUTO_UNMAP, AUTO_UNMAP } unmap_flag;
enum { NO_ENABLE_COA, ENABLE_COA } coa_flag;

const struct dsm_config DEFAULT_DSM_CONFIG = { AUTO_UNMAP, NO_ENABLE_COA };

<more code ...>

#endif

编译时，出现以下错误:

When I compile, I get the following error:

cc -g -Wall -pthread libheca.c dsm_init.c -DDEBUG    master.c   -o master
/tmp/cciBnGer.o:(.rodata+0x0): multiple definition of `DEFAULT_DSM_CONFIG'
/tmp/cckveWVO.o:(.rodata+0x0): first defined here
collect2: ld returned 1 exit status
make: *** [master] Error 1

有什么想法吗?

推荐答案

由于实现文件文件中的每个include，都会创建一个新的struct实例(并将其存储在目标文件中).

Because with every include in a implementation file file, a new instance of your struct is created (and stored in the object file).

为避免这种情况，只需在头文件中将结构声明为"extern"，然后在实现文件中对其进行初始化:

To avoid this, just declare the struct as "extern" in the header file and initialize it in the implementation file:

// In your header file: 
extern const struct dsm_config DEFAULT_DSM_CONFIG;

// In your *.c file:
const struct dsm_config DEFAULT_DSM_CONFIG = { AUTO_UNMAP, NO_ENABLE_COA };

这将解决您的问题.

这篇关于全局变量的多重定义的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！