DLL简单示例

DLL调用方式：

1. 静态调用（编译时链接DLL）
2. 动态调用（运行时显示调用）

代码如下：

• DLL
  • DLL的编译将生成DLL和LIB两个文档（TestDLL.dll、TestDLL.lib）。
  • LIB文档是在编译时用来链接DLL的，称为引用链接库。

#include <windows.h>



// Export this function

extern "C" __declspec(dllexport) double AddNumbers(double a, double b);



// DLL initialization function

BOOL APIENTRY

DllMain(HANDLE hModule, DWORD dwReason, LPVOID lpReserved)

{

	return TRUE;

}



// Function that adds two numbers

double

AddNumbers(double a, double b)

{

	return a + b;

}

• 静态调用
  • TestDLL.lib拷至编译目录下
  • TestDLL.dll拷至exe目录下

#include <windows.h>

#include <stdio.h>

#pragma comment(lib,"TestDLL.lib") //链接引用链接库



// Import function that adds two numbers

extern "C" __declspec(dllimport)double AddNumbers(double a, double b);



int

main(int argc, char **argv)

{

	double result = AddNumbers(1, 2);

	printf("The result was: %f\n", result);



	system("pause");

	return 0;

}

• 动态调用
  • TestDLL.dll拷至exe目录下
  • 无需TestDLL.lib

#include <windows.h>

#include <stdio.h>



// DLL function signature

typedef double (*importFunction)(double, double);



int

main(int argc, char **argv)

{

	importFunction addNumbers;

	double result;



	// Load DLL file

	HINSTANCE hinstLib = LoadLibrary(L"TestDLL.dll");

	if (hinstLib == NULL) {

		printf("ERROR: unable to load DLL\n");

		return 1;

	}



	// Get function pointer

	addNumbers = (importFunction)GetProcAddress(hinstLib, "AddNumbers");

	if (addNumbers == NULL) {

		printf("ERROR: unable to find DLL function\n");

		return 1;

	}



	// Call function.

	result = addNumbers(1, 2);



	// Unload DLL file

	FreeLibrary(hinstLib);



	// Display result

	printf("The result was: %f\n", result);



	system("pause");

	return 0;

}

• 动态调用失败原因：
  1. 调用约定不匹
  2. 导出函数名被修改（可通过Depends.Exe查看导出函数名）
  3. 相应LIB或DLL未拷至相应目录下