Oral examination preparation (iii) -- use dllimport to call unmanaged Functions

Previous ArticleArticleAfter analyzing several methods for making the oral examination system, JMF seems to have a poor reputation, and the client also needs to download the JMF framework, which has never been used by red5 or FMS, microsoft does not seem to provide small web pages like Java appletsProgramBecause the application of the fat client has been occupied by flash, Silverlight has just begun to be promoted. Therefore, I decided to use the C/S architecture.

The first problem to be solved is to call the non-Trust function in the hosting program.

Use dllimport to call Win32 API. dllimport in the namespace system. runtime. interopservices.

Dllimport indicates the declared function.

The usage of dllimport is as follows: [dllimport ("user32.dll", entrypoint = "MessageBox", charset = charset. Auto)]

Here, user32.dll is the name of the DLL to be called, and entrypoint indicates the call entry point, that is, which function in the DLL is called. Charset indicates the called character set. Character sets include ANSI and Unicode.

The functions described by dllimport must be modified using static and extern.

Example:

Declaration prototype:

 

Lipwrap
1 Using System;
2 Using System. Collections. Generic;
3 Using System. text;
4 Using System. runtime. interopservices;
5
6 Namespace Recordtest
7 {
8 Class Lipwrap
9 {
10 [Dllimport ( " User32.dll " , Entrypoint =   " MessageBox " , Charset = Charset. Auto)]
11 Public   Static   Extern   Int Msgbox ( Int Hwnd, string text, string caption, Uint Type );
12 }
13 }
14

 

Call a function

 

Code
1 Using System;
2 Using System. Collections. Generic;
3 Using System. componentmodel;
4 Using System. Data;
5 Using System. drawing;
6 Using System. text;
7 Using System. Windows. forms;
8 Using System. runtime. interopservices;
9
10 Namespace Recordtest
11 {
12 Public   Partial   Class Form1: Form
13 {
14 Public Form1 ()
15 {
16 Initializecomponent ();
17 }
18
19 Private   Void Button#click ( Object Sender, eventargs E)
20 {
21 Lipwrap. msgbox ( 0 , " Hello, world " , " Njj " , 0 );
22 }
23
24
25
26 }
27
28
29
30
31 }

 

After running the program, When you click the button in the window, a hello World pop-up window will appear.

Appendix: managedCodeThe data type of the unmanaged code is incompatible. You must replace the Data Type of the unmanaged code with the data type in the managed code.

The following table lists the Data Types of the managed code corresponding to the unmanaged code from msdn.

 

The following table lists the data types used in Win32 APIs (listed in wtypes. h) and C style functions. Many non-writable libraries contain functions that pass these data types as parameters and return values. The third column lists the corresponding. NET Framework built-in value types or classes used in managed code. In some cases, you can replace the types listed in this table with the same size.

Unmanaged type in wtypes. h	Unmanaged C language type	Managed class name	Description
Handle	Void *		32-bit windows and 64-bit windows.
Byte	Unsigned char		8-digit
Short	Short		16-bit
Word	Unsigned short		16-bit
Int	Int		32-bit
Uint	Unsigned int		32-bit
Long	Long		32-bit
Bool	Long		32-bit
DWORD	Unsigned long		32-bit
Ulong	Unsigned long		32-bit
Char	Char		It is modified with ANSI.
Lpstr	Char *	Or	It is modified with ANSI.
Lpcstr	Const char *	Or	It is modified with ANSI.
Lpwstr	Wchar_t *	Or	Use Unicode.
Lpcwstr	Const wchar_t *	Or	Use Unicode.
Float	Float		32-bit
Double	Double		64-bit

 

The following table describes the commonly used DLL in Win32 APIs.

DLL	Description
Gdi32.dll	Graphical device interface (GDI) functions used for device output, such as functions used for drawing and font management.
Kernel32.dll	Low-level operating system functions for memory management and resource processing.
User32.dll	Windows management functions for message processing, timers, menus, and communication.

 

The multimedia API provided by WIN32API is called MCI, which is included in winmm. dll in the System32 directory.