C + + dynamic link library

1. Dynamic Link Library Overview:

• dynamic-link libraries do not usually run directly or accept messages; it only works when other modules invoke functions in the dynamic-link library.
• All functions in the Windows API are included in the dynamic link library.
• Dynamic link library is divided into static library and dynamic library.

2, the creation of dynamic link library:

The function to be exported is in the form:

extern int Add (intint  b) {      return a +b;   }

To solve the name adaptation problem, you can add a module definition file for the project. def

LIBRARY          MFC-addexports          add    

The classes to be exported are in the form of:

class _declspec (dllexport) point{public:      void OutPut (intint  y);};

Generated after compilation: a DLL (. dll) file, an ingest library (. lib) file, and so on

Note: If you specify an export flag when declaring a class, all functions in the class are exported, otherwise only the class member functions that have the export flags specified when they are declared are exported;

3, dynamic link library loading:

(1) Implicit loading

Use extern or _declspec (dllimport) to declare an external function (preferably write this declaration in a header file *.h)

int Add (intint b);

Import the corresponding ingest library (. lib) file: Link the Lib library in the project settings or use the Code link Lib library in the source file:

#pragma comment (lib, "*.lib")

Add the directory where the dynamic link library file is located to the environment variable in the system: path

(2) Explicit loading

Maps the specified executable module to the address space of the calling process

#include <Windows.h>= LoadLibrary (_t (". \\.. \\MFC-Add\\Debug\\MFC-Add.dll"));

Gets the address of the exported function in the dynamic link library

typedef int (_stdcall *addproc) (int a,int b); // declares that message is a pointer type to a function, the function returns a value of type int; _stdcall is the standard calling convention Addproc Addproc; Addproc  = (addproc) GetProcAddress (handlerdll,_t ("add"));

Calling the Export function

Addproc (5,6);

Release a reference to a DLL when you do not need to access the DLL

FreeLibrary (".. \\.. \\MFC-Add\\Debug\\MFC-add. dll");

Note:

• Dumpbin and Depends Tools
• calling convention: _stdcall: The standard calling convention is the WINAPI calling convention, which is the Pascal calling convention, the non-C calling convention
• Name adaptation: the C + + compiler will name the exported function when it builds the DLL, and the different compilers use different adaptation rules

C + + dynamic link library