Dllexport and dllimport

stay VS in , If you want to use classes or variables across projects , It must be used dllexport and dllimport, The following are examples of global variables , Functions and classes are used across projects .
Environmental preparation ： Use VS Create a new windows Applications and DLL project ,windows The application project name is ConsoleApplication1,DLL Project name: testExtern.


stay ConsoleApplication1 Right click item properties

Additional library directories plus testExtern Generate dll and lib directory

Additional dependencies plus testExtern.lib name

Global variables

In the same project , Global variables do not need to be exported ,extern Just make a statement ：
test.cpp In the definition of ：

int a = 100;

main.cpp Use in ：

extern int a;
int main()
{
    
	cout << a << endl;
}

Output 100;

stay textExtern Define global variables in the project ( Only when the export macro is defined will it generate lib file ), You need to export it ：

int _declspec(dllexport) sssss = 1000000;

stay ConsoleApplication1 Use in sssss This global variable , You need to import ：

extern  int _declspec(dllimport)  sssss;
int main() 
{
    
	cout << sssss << endl;
	return 0;
}

function

Be sure to declare the export when defining the function ：

void _declspec(dllexport) myFun()
{
    
	std::cout << "myFun()" << std::endl;
}

stay main.cpp Contains the declared header file , If the header file is not included, you need extern And declare the import

int main() 
{
    
	myFun();
	return 0;
}

class

stay testExtern In the project ExportClass Must be exported at definition , stay ConsoleApplication1 Must include its header file when used in

class _declspec(dllexport) ExportClass
{
    
public:
	void testExportClass();
};
void ExportClass::testExportClass()
{
    
	std::cout << "textExportClass()" << std::endl;
}

main.cpp in ：

#include "C:\Users\Administrator\Documents\Visual Studio 2015\Projects\ConsoleApplication1\testExtern\extern.h"
int main() 
{
    
	ExportClass ex;
	ex.testExportClass();
	return 0;
}