混合C和C ++全局变量 [英] Mixing C and C++ global variable

问题描述

在我的项目中，我们有一个类似于这样的头文件：

  typedef struct MyStruct 
 { 
 int x; 
} MyStruct; 
 
 externCMyStruct my_struct; 
  

以前，它只包含在C ++源文件中。现在，我需要将它包含在C文件中。所以，我做以下：

  typedef struct MyStruct 
 {
 int x; 
} MyStruct; 
 
 #ifdef __cplusplus 
 externCMyStruct my_struct; 
 #else 
 MyStruct my_struct; 
 #endif 
  

我知道
externC
会将my_struct全局变量声明为C链接，但是这意味着如果我将这个文件包含在C编译文件以及CPP编译文件中，链接器将确定我的意图，在finally链接的可执行文件，我只想要一个用于C和CPP文件的MyStruct使用？

编辑：

采取接受答案的建议。在标题中，我有

  typedef struct MyStruct 
 {
 int x; 
} MyStruct; 
 
 #ifdef __cplusplus 
 externCMyStruct my_struct; 
 #else 
 extern MyStruct my_struct; 
 #endif 
  

在ppp源文件中，我有

  externC{MyStruct my_struct;} 
  

$因为这是头文件，你的C分支应该使用<$ c

$ c> extern 以及：

  #ifdef __cplusplus 
 externCMyStruct my_struct; 
 #else 
 extern MyStruct my_struct; 
 #endif 
  

否则，最终会出现 my_struct 在每个包含标题的翻译单元中，导致在链接阶段出错。

my_struct 应驻留在单独的翻译单元中 - C文件或CPP文件。还需要包含标题，以确保您获得正确的链接。

On my project, we have a header file that looks akin to this:

typedef struct MyStruct
{
  int x;
} MyStruct;

extern "C" MyStruct my_struct;

Previously, it was only included in C++ source files. Now, I have need to include it in C files. So, I do the following:

typedef struct MyStruct
{
  int x;
} MyStruct;

#ifdef __cplusplus
extern "C" MyStruct my_struct;
#else
MyStruct my_struct;
#endif

I understand that extern "C" will declare the my_struct global variable to be of C-linkage, but does this then mean that if I include this file in C-compiled files as well as CPP-compiled files that the linker will determine my intention that in the finally-linked executable, I only want one MyStruct for C and CPP files alike to use?

Edit:

I've taken the advice of the accepted answer. In the header, I have

typedef struct MyStruct
{
  int x;
} MyStruct;

#ifdef __cplusplus
extern "C" MyStruct my_struct;
#else
extern MyStruct my_struct;
#endif

And in the cpp source file, I have

extern "C" {MyStruct my_struct;}

And everything builds.

解决方案

Since this is the header file, your C branch should use extern as well:

#ifdef __cplusplus
extern "C" MyStruct my_struct;
#else
extern MyStruct my_struct;
#endif

Otherwise, you will end up with multiple definitions of the my_struct in every translation unit where the header is included, resulting in errors during the linking phase.

The definition of my_struct should reside in a separate translation unit - either a C file or a CPP file. The header needs to be included as well, to make sure that you get proper linkage.

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