Machine vision Series 1: Visual Studio 2019 dynamic link library DLL establishment

List of articles

Chapter one ：Visual Studio 2019 Dynamic link library DLL establish

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Catalog

List of articles

Preface

One 、DLL What is it? ？

Two 、 Establishment steps

1. install VS

2. establish DLL library

  3、 ... and 、 newly build DLL

  Four 、 compile DLL

summary

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Preface

Recently started a medical machine vision project , Need to use C++, Record some key points .

Environmental Science ：Windows10, VS2019,opencv320

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One 、DLL What is it? ？

Dynamic link library DLL Are some independent documents , It contains programs that can be executed or other dll Call a function to do something , Only when other modules call dll Function in ,dll To work . In actual programming , We can put the function to complete a function in a dynamic link library , And then provide it to other programs to call . image Windows API All the functions in are contained in dll in , Such as Kernel32.dll, User32.dll, GDI32.dll etc. .

Two 、 Establishment steps

1. install VS

Official website , The latest version is 2022

Visual Studio 2022 IDE -  Programming tools for software developers  (microsoft.com)

2. establish DLL library

The code is as follows （ Example ）：

1, New projects

2, Select dynamic link library （DLL）

 3, Set project name , If there is no special need, do not check （ Put the solution and project in the same directory ）

  4, Generate default file , There is no need to modify .

   5, Use the property manager to configure properties , For details, see Chapter 2 of the series .

   6, Modify the precompiled header , Property page ——C/C++—— Precompiled translation head —— Not applicable to precompiled header .

        notes ： If the program is not modified, an error will be reported , I will study it later

  3、 ... and 、 newly build DLL

1, Under the project header , Right click new header (.h), Used to declare the function interface to be exported .

 2, Source files under the project , Right click new source file (.cpp), Used to implement the declared function .

The project catalogue is as follows ：

 

  Now you can write code .

.h file

The function of the following code is to declare a function that can be called “SayHello（）”, Its return type is void.

#pragma once
#include <iostream>

extern "C" __declspec(dllexport) void SayHello();

Now analyze extern "C" __declspec(dllexport) void SayHello(); This code , among extern "C" The function of is to tell the compiler to press C Language , The significance of doing so is not discussed here , If you are interested, you can inquire by yourself . Then analysis __declspec(dllexport), This modifier tells the compiler and linker that the function or variable it modifies needs to be from DLL export , For use by other applications ; In contrast, another code is __declspec(dllimport), The purpose of this modifier is to tell the compiler and linker that the function or variable modified by it needs to be from DLL Import , It will also be used later . Finally, the function void SayHello(), It is the function that needs to be called by other programs .

.cpp file

Realization .h Functions declared in the file

#include "pch.h"
#include "TestDLL.h"

void SayHello()
{
	std::cout << "Hello！ You did it ！" << std::endl;
}

Code writing completed .

  Four 、 compile DLL

If the attribute environment is ok , Click on the compilation

  Click compile to pop up below , Click on the confirmation （DLL Will not generate exe, Ignore the error report ）

In the project path ——x64——debug Generate files under folder .

Compile the complete .

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summary

1、 The above tutorial is only applicable to debugging mode , If you want to start directly TestDLLCreated.exe Applications , You still need to “TestDLL.dll” and “TestDLL.lib” Copy the file to TestDLLCreated.exe Only under the same directory can it run ！

2、 You can use the property manager to configure properties , Other items can use attributes directly , Avoid duplicate settings .

Reference resources ：https://blog.csdn.net/elaine_bao/article/details/51784864