DLL 共享数据学习

要想在DLL共享数据，必须重新定义一个共享段，然后用函数去修改添加

DLL代码：

#include "stdafx.h"

#pragma data_seg("MyData")                                  //定义一个共享段
int name=10;
#pragma data_seg
#pragma comment(linker,"/section:MyData,rws")

extern "C"  _declspec(dllexport) int add(void)             //用函数去操作它
{
	return name*5;
}
extern "C"  _declspec(dllexport) int letdown(void)
{
	name = name - 1;
	return name*5;
}

BOOL APIENTRY DllMain( HANDLE hModule, 
                       DWORD  ul_reason_for_call, 
                       LPVOID lpReserved
					 )
{
	switch (ul_reason_for_call)
	{
	case DLL_PROCESS_ATTACH:
		MessageBox(NULL,"DLL载入","OK",NULL);
		break;
	case DLL_PROCESS_DETACH:
		MessageBox(NULL,"DLL卸载","OK",NULL);
		break;
	}
    return TRUE;

应用程序1)

#include "stdafx.h"
#include <windows.h>
#include <process.h>

int main(int argc, char* argv[])
{
	char str[] = "C:\Documents and Settings\Administrator\桌面\test\Dlltest.dll";
	FARPROC procaddress = GetProcAddress(LoadLibraryA(str),"letdown");
	
	int recv = procaddress();
	printf("name = %d
",recv);
	system("pause");
	return 0;
}

应用程序2)

#include "stdafx.h"
#include <windows.h>
#include <process.h>

int main(int argc, char* argv[])
{
	FARPROC procaddress = GetProcAddress(LoadLibraryA("Dlltest.dll"),"add");
	int recv = procaddress();
	printf("name = %d
",recv);
	system("pause");


	return 0;
}

效果：

先用 程序1  改变了 name值 运行后  输出9*5

然后程序2运行 如果是共享内存的话  还是输出9*5  共享成功

但如果 没有设置  #pragma data_seg 的话   每个EXE调用的DLL  都是独立的