怎么用C++调用API

c#在调用c++方法或者window api时不能象调用c#本身写的dll类库那样直接通过引用dll就可以调用相应的方法,
而是要把要引用的dll放到bin中,现通过[DllImport("um_web_client.dll")]引用

例子1如下:

//声明部分

[DllImport("um_web_client.dll")]
private static extern int
CheckUserName(string UserName);

//

public static int AuthUserName(string username)
{

if(!IsConnection())
{

StartWebClient(UDBClientIP,UDBClientPort,UDBClientTimeout);
}
return
CheckUserName(username);
}

但是如果c++方法中用了指针或者结构体等则引用就要注意,相应就要用到引用数组或者指针,例子2:

声明部分

复制代码 代码如下:
StructLayout(LayoutKind.Sequential, CharSet=CharSet.Ansi )]
public class
tagPlayerInfoOut
{
public int id;
public String
PlayerName;
public int Country;
public int OfficerRace;
public
int Level;
public int MilitaryRank;
public int Money;
public
int ResourceCount;
public int CityCount;
public int
GeneralCount;
public int Credit;
}

[ StructLayout( LayoutKind.Sequential )]
public struct
tagPlayerInfoOutEx
{
public int id;
public IntPtr
PlayerName;
public int Country;
public int OfficerRace;
public
int Level;
public int MilitaryRank;
public int Money;
public
int ResourceCount;
public int CityCount;
public int
GeneralCount;
public int Credit;
}

[DllImport("um_web_client.dll")]
public static extern int
GetPlayerListCs(int maxrows, out int rows, out IntPtr playerlist);

[DllImport("um_web_client.dll")]
public static extern int
GetPlayerListCs(int maxrows, out int rows, tagPlayerInfoOutEx**
playerlist);

方法

代码如下:
public static DataTable UsingMarshal()
{
if(!IsConnection())

{
StartWebClient(UDBClientIP,UDBClientPort,UDBClientTimeout);

}
DataTable dt = new DataTable();

dt.Columns.Add("id");
dt.Columns.Add("PlayerName");

dt.Columns.Add("Country");
dt.Columns.Add("OfficerRace");

dt.Columns.Add("Level");
dt.Columns.Add("MilitaryRank");

dt.Columns.Add("Money");
dt.Columns.Add("ResourceCount");

dt.Columns.Add("CityCount");
dt.Columns.Add("GeneralCount");

dt.Columns.Add("Credit");

int size = 0;
IntPtr outArray;
GetPlayerListCs(20, out size,
out outArray);
tagPlayerInfoOut[] manArray = new
tagPlayerInfoOut[size];
IntPtr current = outArray;

//Console.WriteLine("记录数{0}",size);

for( int i = 0; i < size; i++
)
{
manArray[ i ] = new tagPlayerInfoOut();

Marshal.PtrToStructure(current, manArray[i]);

Marshal.DestroyStructure(current, typeof(tagPlayerInfoOut) );
current =
(IntPtr)((long)current + Marshal.SizeOf(manArray[i]));

dt.Rows.Add(new object[]
{manArray[i].id,manArray[i].PlayerName,manArray[i].Country,manArray[i].OfficerRace,manArray[i].Level,manArray[i].MilitaryRank,manArray[i].Money,manArray[i].ResourceCount,manArray[i].CityCount,manArray[i].GeneralCount,manArray[i].Credit});

dt.AcceptChanges();
//Console.WriteLine( "Element {0}: {1} {2}", i,
manArray[i].id, manArray[i].PlayerName);
}

Marshal.FreeCoTaskMem(outArray);
return dt;
}

public static unsafe DataTable UsingUnsafe()
{
int size;

if(!IsConnection())
{

StartWebClient(UDBClientIP,UDBClientPort,UDBClientTimeout);
}

DataTable dt = new DataTable();

dt.Columns.Add("id");
dt.Columns.Add("PlayerName");

dt.Columns.Add("Country");
dt.Columns.Add("OfficerRace");

dt.Columns.Add("Level");
dt.Columns.Add("MilitaryRank");

dt.Columns.Add("Money");
dt.Columns.Add("ResourceCount");

dt.Columns.Add("CityCount");
dt.Columns.Add("GeneralCount");

dt.Columns.Add("Credit");
tagPlayerInfoOutEx* pResult;

GetPlayerListCs(20, out size, &pResult );
tagPlayerInfoOutEx*
pCurrent = pResult;
//Console.WriteLine("记录数{0}",size);

for( int i = 0; i < size; i++, pCurrent++ )
{

//Console.WriteLine( "Element {0}: {1} {2}", i, pCurrent->id
,Marshal.PtrToStringAnsi(pCurrent->PlayerName));

//Marshal.FreeCoTaskMem(pCurrent->PlayerName );
dt.Rows.Add(new
object[]
{pCurrent->id,pCurrent->PlayerName,pCurrent->Country,pCurrent->OfficerRace,pCurrent->Level,pCurrent->MilitaryRank,pCurrent->Money,pCurrent->ResourceCount,pCurrent->CityCount,pCurrent->GeneralCount,pCurrent->Credit});

dt.AcceptChanges();
}
Marshal.FreeCoTaskMem((IntPtr)pResult
);
return dt;
}

首先搞清楚你要用的API在哪个库里，然后将这个头文件包进来。。有的还要用到lib..
比如：
#include "windows.h"
TextOut(hdc, x, y, psText, iLength) ;

TextOut为windows.h中的API函数

和调用你自己定义的函数一样的
比如
int Sleep(int minisecond);

in windows.h

====================
#include

void main()
{
Sleep(1000);//wait 1 second
}

#include 后就可以调用了

include 后就可以调用了