#ifdef WIN32DLL_EXPORTS是什么意思？

Question

我已经创建了一个DLL文件,在头文件中我看到:

#ifdef WIN32DLL_EXPORTS

我不明白它是什么意思,我们在哪里/如何设置WIN32DLL_EXPORTS.

如果我使用:

#ifdef WIN32DLL_EXPORTS
    #define WIN32DLL_API __declspec(dllexport)
#else
    #define WIN32DLL_API __declspec(dllimport)
#endif

WIN32DLL_API int testSum(void);

testSum被认为是__declspec(dllimport).所以我认为我的项目没有设定WIN32DLL_EXPORTS？我怎么能改变这个？

Answer 1

在您引用的行的正上方有一个注释块.阅读.

// The following ifdef block is the standard way of creating macros which make exporting 
// from a DLL simpler. All files within this DLL are compiled with the WIN32DLL_EXPORTS
// symbol defined on the command line. this symbol should not be defined on any project
// that uses this DLL. This way any other project whose source files include this file see 
// WIN32DLL_API functions as being imported from a DLL, wheras this DLL sees symbols
// defined with this macro as being exported.
#ifdef WIN32DLL_EXPORTS
#define WIN32DLL_API __declspec(dllexport)
#else
#define WIN32DLL_API __declspec(dllimport)
#endif