12. Dynamic link library, DLL

Dynamic link libraries usually cannot run directly , Can't receive messages . They're separate files , It includes executable programs or other DLL Call a function to do something . Only when other modules call functions in the dynamic link library , It works .

1、 We can put functions that perform certain functions in a DLL , Provided to other function calls .Windows API All the functions in are contained in DLL in , Three of the most important ：

1）Kernal32.dll Include those for memory management , Functions of processes and threads , Such as CreateThread function .

2）User32.dll Includes performing user interface tasks , Functions such as window creation and message transmission , Such as 3）CreateWindow function .

3）GDI32.dll A function that displays text for drawing .

2、 Static library and dynamic library ：

Static library ：

Functions and data are compiled into a binary file （ Usually the extension is .LIB）. In the case of using static libraries , When compiling linked executables , The linker copies these functions and data from the library and combines them with other modules of the application to create the final executable . There is no need to publish the used static library when publishing products .

Dynamic library ：

Dynamic libraries generally provide two files ： A lead in warehouse （.lib）, One is DLL（.dll） file ..lib The file contains this DLL Symbolic names of exported functions and variables , and .dll The file contains the DLL Actual functions and data . When using dynamic library , When compiling linked executables , Just link to the DLL Import library file , The DLL The function code and data in are not copied to the executable , Until the executable runs , To load the required DLL, Will be DLL Map to the address space of the process , And then visit DLL Functions exported in . Release products at the same time DLL.

Icon P703 Two processes access the same DLL Situation of time

Two kinds of loading dll How to file , Implicit loading and explicit loading .

3、Dumpbin command

If an application wants to access a DLL The function in , Then the function must be an exported function . It can be used Dumpbin see . You may need to pass VCVARS32.bat To establish the VC Environment variables used .

dumpbin -exports name.dll

4、 export DLL Middle function

Add _declspec(dllexport) In front of the function .

1） Implicitly load

（1） adopt extern Declare external functions . And enter lib Symbol name file . hold dll Document and lib The file is placed in the specified directory in the VC++ The catalog contains .

（2） utilize _declspec(dllimport) Before the external function is declared .

For convenience dll Use , It usually provides a .h Documents for customers ; We usually handle the function declaration in the header file as follows ：

#ifdef DLL1_API
#else
#define DLL1_API _declspec(dllimport)
#endif

DLL1_API int _stdcall add(int a,int b);

Copy

And in the function definition .cpp In file , The following form defines ：

#define DLL1_API extern "C" _declspec(dllexport)
#include "Dll1.h"

#include <Windows.h>
#include <stdio.h>

int _stdcall add(int a,int b)
{
return a+b;
}

Copy

In this way, no additional code changes are required when providing to customers .

Again , You can define the above DLL1 Add in front of a class , Or class member function to export the class or class member function . As shown below ：

class /*DLL1*/ Point
{
public:
void DLL1_API output(int x,int y);
void test();
};

Copy

2） Explicitly load

adopt LoadLibrary To achieve .LoadLibrary Map the specified executable module to the address space of the calling process ,and the return value is a handle to the module. Re pass GetProcAddress To get the address of the exported function in the dynamic library .

HINSTANCE hInst;
hInst=LoadLibrary("Dll3.dll");
typedef int (/*_stdcall*/ *ADDPROC)(int a,int b);
//ADDPROC Add=(ADDPROC)GetProcAddress(hInst,"[email protected]@[email protected]");
ADDPROC Add=(ADDPROC)GetProcAddress(hInst,"add");
//ADDPROC Add=(ADDPROC)GetProcAddress(hInst,MAKEINTRESOURCE(1));

Copy

The MAKEINTRESOURCE macro converts an integer value to a resource type

compatible with the resource-management functions. This macro is used in place of a

string containing the name of the resource

The DllMain function is called when the driver DLL first starts up.

After use , adopt FreeLibrary To reduce the load dll Reference count of , When it comes to 0 when , The DLL The module is unloaded from the address space of the calling process .

5、 Name adaptation

Different compilers compile functions , And when using different function calling conventions , The adaptation of functions is different .

http://www.cnblogs.com/mydomain/archive/2010/09/27/1837179.html

thus , There will be some problems when calling functions , If used C++ The functions generated by the compiler pass C There will be an error when the compiler calls . In this case , You can add extern “C”

#define DLL1_API extern “C” _declspec(dllimport)

utilize extern “C” Can solve C++,C Inter call problem , But there is one flaw , It can't be used to export member functions of a class ., It can only be used to export global functions .

If the calling convention of the function changes , If some functions use _stdcall, Some use pascal, So even if you use extern “C”, Name adaptation will still happen .

You can define a module definition file .def The way to solve this problem ：

Create a new one newname.def file , Join the project ：

LIBRARY Dll2
EXPORTS
add
subtract

Copy

Dll2 The name is the same as the generated dynamic link library .

EXPORTS： If the symbol name defined below is the same as the function name , Then export the function with a symbolic name , If different , Export functions according to the following rules ：

entryname[=internalname] [@ordinal[NONAME]] [DATA] [PRIVATE]

There are three methods for exporting a definition, listed in recommended order of use:

1.The __declspec(dllexport) keyword in the source code

2.An EXPORTS statement in a .def file

3.An /EXPORT specification in a LINK command[1]

Reference resources ：

[1] http://msdn.microsoft.com/en-us/library/hyx1zcd3.aspx

[2] VC++ Go into detail

Publisher ： Full stack programmer stack length , Reprint please indicate the source ：https://javaforall.cn/110679.html Link to the original text ：https://javaforall.cn