使用P / Invoke如何马歇尔C ++的char *到C＃字符串 [英] How to marshall c++ char* to C# string using P/INVOKE

问题描述

我是新的C ++。我打电话从C＃使用的PInvoke C ++函数，并希望得到一个字符串作为回out参数。不过，我只是得到一个空字符串返回。通过int out参数正常工作。

导入：

 函数[DllImport（@UnamanagedAssembly.dll ，字符集= CharSet.Ansi）] 
公共静态外部INT激活（REF INT numActivated，StringBuilder的eventsActivated）; 
 
的externC__declspec（dllexport）的INT激活（INT * p_NumActivated，字符* p_EventsActivated）{返回激活::的GetInstance（） -  GT;激活（p_NumActivated，p_EventsActivated）;} 
  

调用我的C ++从C＃功能：

  INT numActivated = 0; 
 StringBuilder的eventsActivated =新的StringBuilder（）; 
 INT状态=激活（REF numActivated，eventsActivated）; 
  

C ++函数：

  INT激活::激活（INT * p_NumActivated，字符*&安培; p_EventsActivated）
 {
的char * PTEMP =你好; 
 p_EventsActivated = PTEMP; 
 
 * p_NumActivated = 1; 
 
返回0; 
} 
  

解决方案

 函数[DllImport（@UnamanagedAssembly.dll，字符集= CharSet.Ansi）] 
公共静态外部INT激活（
 REF INT numActivated，
 [的MarshalAs（UnmanagedType.LPStr） StringBuilder的eventsActivated）; 
  

I'm new to C++. I'm calling a C++ function from C# using a PINVOKE and wanting to get a string back as an out parameter. However I just get an empty string back. The int out parameter works fine.

Importing:

[DllImport ( @"UnamanagedAssembly.dll", CharSet = CharSet.Ansi)] 
public static extern int Activate(ref int numActivated,  StringBuilder eventsActivated);

extern "C" __declspec(dllexport) int Activate(int *p_NumActivated, char *p_EventsActivated) {return Activation::GetInstance()->Activate(p_NumActivated, p_EventsActivated);}

Calling my C++ function from C#:

int numActivated = 0;
StringBuilder eventsActivated = new StringBuilder();
int status = Activate(ref numActivated, eventsActivated);  

The C++ function:

int Activation::Activate(int *p_NumActivated, char *&p_EventsActivated)
{
    char *pTemp = "Hello";
    p_EventsActivated = pTemp;

    *p_NumActivated = 1;

    return 0;
}

解决方案

[DllImport ( @"UnamanagedAssembly.dll", CharSet = CharSet.Ansi)]
public static extern int Activate(
    ref int numActivated, 
    [MarshalAs(UnmanagedType.LPStr)]StringBuilder eventsActivated);

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