VS2017创建动态库DLL，并实现调用

1、打开VS2017，新建一个"动态链接库（DLL）"项目，这里命名为“MyFirstDll”

2、建好后的项目中，在头文件中会自动生成framework.h和pch.h两个文件，在源文件中会自动生成dllmain.cpp和pch.cpp两个文件

3、在头文件中新建一个MathLibrary.h文件，用于函数的声明。

在源文件中新建一个MathLibrary.cpp文件，用于函数的实现。

代码用例是实现Fibonacci生兔子的例子

// MathLibrary.h
#pragma once
// import 进口，输入
// export 出口，输出
#ifdef MATHLIBRARY_EXPORTS
#define MATHLIBRARY_API __declspec(dllexport)
#else
#define MATHLIBRARY_API __declspec(dllimport)
#endif

// The Finoacci recurrence relation describes a sequence F
// where F(n) is { n = 0, a
//               { n = 1, b
//               { n >1, F(n-2) + F(n-1)
// for some initial intergral values a and b.
// If the sequence is initialized F(0) = 1, F(1) = 1,
// then this relation produces the well-known Fibonacci
// sequence: 1, 1, 2, 3, 5, 8, 13, 21, 34, ...

// initialize a Fibonacci relation sequence
// such that F(0) = a, F(1) = b.

// this function must be called before any other function
extern "C" MATHLIBRARY_API void fibonacci_init(const unsigned long long a, const unsigned long long b);

// produce the next value in the sequence .
// returns true on success and updates current value and index;
// false on overflow, leaves current value and index unchanged.
extern "C" MATHLIBRARY_API bool fibonacci_next();

// get the current value in the sequence.
extern "C" MATHLIBRARY_API unsigned long long fibonacci_current();

// get the position of the current value in the sequence
extern "C" MATHLIBRARY_API unsigned fibonacci_index();

 

// MathLibrary.cpp: Defines the exported function for the Dll
// #include"stdafx.h"
#include"pch.h"
#include<utility>
#include<limits.h>
#include"MathLibrary.h"

// Dll internal state variables:
static unsigned long long previous_;  // previous  value, if any  
static unsigned long long current_;   // current sequence value
static unsigned index_;               // current seq. Position

// initialize a fibonacci relation sequence
// such that F(0) = a, F(1) = b.
// This function must be called before any other function.
void fibonacci_init(const unsigned long long a, const unsigned long long b)
{
	index_ = 0; 
	current_ = a;
	previous_ = b; // see special case when initialized

}

// produce the next value in the sequence
// return true on success, false on overflow.
bool fibonacci_next()
{
	// check to see if we'd overflow result or position
	if ((ULLONG_MAX - previous_ < current_) || (UINT_MAX == index_))
	{
		return false;
	}

	if (index_ > 0)
	{
		previous_ += current_;
	}

	std::swap(current_, previous_);
	++index_;
	return true;
}

unsigned long long fibonacci_current()
{
	return current_;
}

unsigned fibonacci_index()
{
	return index_;
}

我这里是在realease x64下运行，所以在与项目名同目录下的x64中会生成一个release文件夹

测试dll文件

1、打开VS2017新建一个空项目，命名为testDll2

2、将之前生成的MyFirstDll.dll、MyFirstDll.lib和MathLibrary.h文件复制到项目文件中。

3、在testDll2中的头文件夹中，将MathLibrary.h添加进来、在资源文件中将MyFirstDll.lib添加进来。

4、开始测试用例，在testDll2.cpp中添加如下代码：

#include <iostream>
#include"MathLibrary.h"

int main()
{
	std::cout << "Hello World!\n";
	fibonacci_init(1, 1);
	do
	{
		std::cout << fibonacci_index() << ":"
			<< fibonacci_current() << std::endl;
	} while (fibonacci_next());

	// report count of values written before overflow
	std::cout << fibonacci_index() + 1 <<
		"Fibonacci sequence values fit in an " <<
		"unsigned 64-bit interger. " << std::endl;

}

.dll和.lib文件是在release x64下生成的，所以，运用时也需要在release x64下运行。运行结果：