如何优雅的导出函数

在开发过程中，经常会引用外部函数。方法主要有两种：

方法一：包含头文件并制定lib位置

• 优点：使用简单
• 缺点：lib和vs版本有关，不同的版本和编译模式可能导致编译失败

方法二：GetProcAddress

• 优点：和编译器无关，只要获取函数地址即可使用
• 缺点：需要一个个的函数去获取地址，相对麻烦

思考：有没有好的导出方式，可以直接包含头文件就使用呢？

• 答案：有，参考Miniblink。在使用Miniblink的时候我们只需要包含头文件就可以直接引用导出函数。

源码分析：

1. 作为dll的开发者，需要导出函数。模式如下：

#if defined(__cplusplus)
#define XYCENTER_EXTERN_C extern "C" 
#else
#define XYCENTER_EXTERN_C 
#endif#这里定义宏，根据函数参数个数不同，定义如下函数，一直延续到NXYCENTER_DEFINE_ITERATORN
#define XYCENTER_DECLARE_ITERATOR0(returnVal, name, description) \XYCENTER_EXTERN_C __declspec(dllexport) returnVal name();#define XYCENTER_DECLARE_ITERATOR1(returnVal, name, p1, description) \XYCENTER_EXTERN_C __declspec(dllexport) returnVal name(p1);#define XYCENTER_DECLARE_ITERATOR2(returnVal, name, p1, p2, description) \XYCENTER_EXTERN_C __declspec(dllexport) returnVal name(p1, p2);#格式按照【返回类型】【函数名】【参数】来维护导出函数列表0-N
#define XYCENTER_FOR_EACH_DEFINE_FUNCTION(ITERATOR0, ITERATOR1，ITERATOR2) \ITERATOR0(void, xyShutdown, "") \ITERATOR1(void, set_xycenterlog_handle,char *,"") \

#导出所有的函数0-N
XYCENTER_FOR_EACH_DEFINE_FUNCTION(XYCENTER_DECLARE_ITERATOR0, XYCENTER_DECLARE_ITERATOR1)

实现对应的导出函数即可：

void xyShutdown(){}
void set_xycenterlog_handle(char *){}

2. 作为dll的符号使用者，分为两个步骤定义函数指针和对象，获取对应的符号地址

#定义不同参数个数的函数指针以及对应的对象0-N
#selectany 关键字，相关含义可以自行搜索
#define XYCENTER_DEFINE_ITERATOR0(returnVal, name, description) \typedef returnVal(XYCENTER_CALL_TYPE* xyFN_##name)(); \__declspec(selectany) xyFN_##name name = ((xyFN_##name)0);#define XYCENTER_DEFINE_ITERATOR1(returnVal, name, p1, description) \typedef returnVal(XYCENTER_CALL_TYPE* xyFN_##name)(p1); \__declspec(selectany) xyFN_##name name = ((xyFN_##name)0);#define XYCENTER_DEFINE_ITERATOR2(returnVal, name, p1,p2, description) \typedef returnVal(XYCENTER_CALL_TYPE* xyFN_##name)(p1,p2); \__declspec(selectany) xyFN_##name name = ((xyFN_##name)0);#获取函数地址
#define XYCENTER_GET_PTR_ITERATOR(name) \name = (xyFN_##name)GetProcAddress(hMod, #name); \if (!name) \MessageBoxA(((HWND)0), #name##" api not found", #name, 0);
#为了兼容上述维护的函数列表，所以需要多对应获取0-N的参数模式，这里直接使用变参模式
#define XYCENTER_GET_PTR_ITERATORN(returnVal, name,...) \XYCENTER_GET_PTR_ITERATOR(name);#最后一步设置dll路径并且初始化
#for each 不同参数的函数地址
XYCENTER_FOR_EACH_DEFINE_FUNCTION(XYCENTER_DEFINE_ITERATOR0, XYCENTER_DEFINE_ITERATOR1, XYCENTER_DEFINE_ITERATOR2)__declspec(selectany) const wchar_t* s_xyCenterDllPath = L"xyCenter.dll";inline void xyCenterSetWkeDllPath(const wchar_t* dllPath)
{s_xyCenterDllPath = dllPath;
}inline int xyCenterInitialize()
{HMODULE hMod = NULL;if (!hMod)hMod = LoadLibraryW(s_xyCenterDllPath);if (hMod) {XYCENTER_FOR_EACH_DEFINE_FUNCTION(XYCENTER_GET_PTR_ITERATORN, XYCENTER_GET_PTR_ITERATORN, XYCENTER_GET_PTR_ITERATORN);return 1;}return 0;
}

完整头文件，目前默认支持最多10个参数，用户可以自己扩展

使用宏XYCENTER_EXPORTS来决定是导入函数还是导出函数

#ifndef XYCENTER_DEFINE_H
#define XYCENTER_DEFINE_H#include <windows.h>//
#define XYCENTER_CALL_TYPE __cdecl#if defined(__cplusplus)
#define XYCENTER_EXTERN_C extern "C" 
#else
#define XYCENTER_EXTERN_C 
#endifnamespace xyCenter
{
#pragma pack(pop)/定义函数指针以及变量/
#define XYCENTER_DEFINE_ITERATOR0(returnVal, name, description) \typedef returnVal(XYCENTER_CALL_TYPE* xyFN_##name)(); \__declspec(selectany) xyFN_##name name = ((xyFN_##name)0);#define XYCENTER_DEFINE_ITERATOR1(returnVal, name, p1, description) \typedef returnVal(XYCENTER_CALL_TYPE* xyFN_##name)(p1); \__declspec(selectany) xyFN_##name name = ((xyFN_##name)0);#define XYCENTER_DEFINE_ITERATOR2(returnVal, name, p1,p2, description) \typedef returnVal(XYCENTER_CALL_TYPE* xyFN_##name)(p1,p2); \__declspec(selectany) xyFN_##name name = ((xyFN_##name)0);#define XYCENTER_DEFINE_ITERATOR3(returnVal, name, p1,p2,p3, description) \typedef returnVal(XYCENTER_CALL_TYPE* xyFN_##name)(p1,p2,p3); \__declspec(selectany) xyFN_##name name = ((xyFN_##name)0);#define XYCENTER_DEFINE_ITERATOR4(returnVal, name, p1,p2,p3,p4, description) \typedef returnVal(XYCENTER_CALL_TYPE* xyFN_##name)(p1,p2,p3,p4); \__declspec(selectany) xyFN_##name name = ((xyFN_##name)0);#define XYCENTER_DEFINE_ITERATOR5(returnVal, name, p1,p2,p3,p4,p5, description) \typedef returnVal(XYCENTER_CALL_TYPE* xyFN_##name)(p1,p2,p3,p4,p5); \__declspec(selectany) xyFN_##name name = ((xyFN_##name)0);#define XYCENTER_DEFINE_ITERATOR6(returnVal, name, p1,p2,p3,p4,p5,p6, description) \typedef returnVal(XYCENTER_CALL_TYPE* xyFN_##name)(p1,p2,p3,p4,p5,p6); \__declspec(selectany) xyFN_##name name = ((xyFN_##name)0);#define XYCENTER_DEFINE_ITERATOR7(returnVal, name, p1,p2,p3,p4,p5,p6,p7, description) \typedef returnVal(XYCENTER_CALL_TYPE* xyFN_##name)(p1,p2,p3,p4,p5,p6,p7); \__declspec(selectany) xyFN_##name name = ((xyFN_##name)0);#define XYCENTER_DEFINE_ITERATOR8(returnVal, name, p1,p2,p3,p4,p5,p6,p7,p8, description) \typedef returnVal(XYCENTER_CALL_TYPE* xyFN_##name)(p1,p2,p3,p4,p5,p6,p7,p8); \__declspec(selectany) xyFN_##name name = ((xyFN_##name)0);#define XYCENTER_DEFINE_ITERATOR9(returnVal, name, p1,p2,p3,p4,p5,p6,p7,p8,p9, description) \typedef returnVal(XYCENTER_CALL_TYPE* xyFN_##name)(p1,p2,p3,p4,p5,p6,p7,p8,p9); \__declspec(selectany) xyFN_##name name = ((xyFN_##name)0);#define XYCENTER_DEFINE_ITERATOR10(returnVal, name, p1,p2,p3,p4,p5,p6,p7,p8,p9,p10, description) \typedef returnVal(XYCENTER_CALL_TYPE* xyFN_##name)(p1,p2,p3,p4,p5,p6,p7,p8,p9,p10); \__declspec(selectany) xyFN_##name name = ((xyFN_##name)0);/获取dll函数指针地址/
#define XYCENTER_GET_PTR_ITERATOR(name) \name = (xyFN_##name)GetProcAddress(hMod, #name); \if (!name) \MessageBoxA(((HWND)0), #name##" api not found", #name, 0);#define XYCENTER_GET_PTR_ITERATORN(returnVal, name,...) \XYCENTER_GET_PTR_ITERATOR(name);/定义导出函数/
#define XYCENTER_DECLARE_ITERATOR0(returnVal, name, description) \XYCENTER_EXTERN_C __declspec(dllexport) returnVal name();#define XYCENTER_DECLARE_ITERATOR1(returnVal, name, p1, description) \XYCENTER_EXTERN_C __declspec(dllexport) returnVal name(p1);#define XYCENTER_DECLARE_ITERATOR2(returnVal, name, p1, p2, description) \XYCENTER_EXTERN_C __declspec(dllexport) returnVal name(p1, p2);#define XYCENTER_DECLARE_ITERATOR3(returnVal, name, p1, p2,p3, description) \XYCENTER_EXTERN_C __declspec(dllexport) returnVal name(p1, p2,p3);#define XYCENTER_DECLARE_ITERATOR4(returnVal, name, p1, p2,p3,p4, description) \XYCENTER_EXTERN_C __declspec(dllexport) returnVal name(p1, p2,p3,p4);#define XYCENTER_DECLARE_ITERATOR5(returnVal, name, p1, p2,p3,p4,p5, description) \XYCENTER_EXTERN_C __declspec(dllexport) returnVal name(p1, p2,p3,p4,p5);#define XYCENTER_DECLARE_ITERATOR6(returnVal, name, p1, p2,p3,p4,p5,p6, description) \XYCENTER_EXTERN_C __declspec(dllexport) returnVal name(p1, p2,p3,p4,p5,p6);#define XYCENTER_DECLARE_ITERATOR7(returnVal, name, p1, p2,p3,p4,p5,p6,p7, description) \XYCENTER_EXTERN_C __declspec(dllexport) returnVal name(p1, p2,p3,p4,p5,p6,p7);#define XYCENTER_DECLARE_ITERATOR8(returnVal, name, p1, p2,p3,p4,p5,p6,p7,p8, description) \XYCENTER_EXTERN_C __declspec(dllexport) returnVal name(p1, p2,p3,p4,p5,p6,p7,p8);#define XYCENTER_DECLARE_ITERATOR9(returnVal, name, p1, p2,p3,p4,p5,p6,p7,p8,p9, description) \XYCENTER_EXTERN_C __declspec(dllexport) returnVal name(p1, p2,p3,p4,p5,p6,p7,p8,p9);#define XYCENTER_DECLARE_ITERATOR10(returnVal, name, p1, p2,p3,p4,p5,p6,p7,p8,p9,p10, description) \XYCENTER_EXTERN_C __declspec(dllexport) returnVal name(p1, p2,p3,p4,p5,p6,p7,p8,p9,p10);// 以下是xyCenter的导出函数。格式按照【返回类型】【函数名】【参数】来排列
#define XYCENTER_FOR_EACH_DEFINE_FUNCTION(ITERATOR0, ITERATOR1,ITERATOR2,ITERATOR3,ITERATOR4,ITERATOR5,ITERATOR6,ITERATOR7,ITERATOR8,ITERATOR9,ITERATOR10) \ITERATOR0(int, get_msgno, "获取通知消息的消息code") \ITERATOR1(void, set_log_handle, PFN_XYCENTERLOG_HANDLE,"设置日志句柄") \ITERATOR1(bool, write_data, XyCenterData *,"写入用户共享数据") \ITERATOR1(bool, read_data, XyCenterData&,"获取用户数据") \
//导出函数
#ifdef XYCENTER_EXPORTSXYCENTER_FOR_EACH_DEFINE_FUNCTION(XYCENTER_DECLARE_ITERATOR0, XYCENTER_DECLARE_ITERATOR1, XYCENTER_DECLARE_ITERATOR2,\XYCENTER_DECLARE_ITERATOR3,XYCENTER_DECLARE_ITERATOR4, XYCENTER_DECLARE_ITERATOR5, XYCENTER_DECLARE_ITERATOR6,\XYCENTER_DECLARE_ITERATOR7, XYCENTER_DECLARE_ITERATOR8,XYCENTER_DECLARE_ITERATOR9, XYCENTER_DECLARE_ITERATOR10)//引入导出函数
#elseXYCENTER_FOR_EACH_DEFINE_FUNCTION(XYCENTER_DEFINE_ITERATOR0, XYCENTER_DEFINE_ITERATOR1, XYCENTER_DEFINE_ITERATOR2,\XYCENTER_DEFINE_ITERATOR3, XYCENTER_DEFINE_ITERATOR4, XYCENTER_DEFINE_ITERATOR5, XYCENTER_DEFINE_ITERATOR6,\XYCENTER_DEFINE_ITERATOR7, XYCENTER_DEFINE_ITERATOR8, XYCENTER_DEFINE_ITERATOR9, XYCENTER_DEFINE_ITERATOR10)__declspec(selectany) const wchar_t* s_xyCenterDllPath = L"xyCenter.dll";inline void SetWkeDllPath(const wchar_t* dllPath){s_xyCenterDllPath = dllPath;}inline bool Initialize(){HMODULE hMod = NULL;if (!hMod)hMod = LoadLibraryW(s_xyCenterDllPath);if (hMod) {XYCENTER_FOR_EACH_DEFINE_FUNCTION(XYCENTER_GET_PTR_ITERATORN, XYCENTER_GET_PTR_ITERATORN, XYCENTER_GET_PTR_ITERATORN,\XYCENTER_GET_PTR_ITERATORN, XYCENTER_GET_PTR_ITERATORN, XYCENTER_GET_PTR_ITERATORN, XYCENTER_GET_PTR_ITERATORN,\XYCENTER_GET_PTR_ITERATORN, XYCENTER_GET_PTR_ITERATORN, XYCENTER_GET_PTR_ITERATORN, XYCENTER_GET_PTR_ITERATORN);return true;}return false;}
#endif // DEBUG#endif // XYCENTER_DEFINE_H};

此时我们只需要包含头文件，并且初始化一下即可直接使用导出函数。