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