从本机C ++ DLL传递字符串到C＃应用程序 [英] Passing String from Native C++ DLL to C# App

问题描述

我已经用C ++编写的DLL。其中一个功能写入一个字符数组。

I have written a DLL in C++. One of the functions writes to a character array.

C ++函数

EXPORT int xmain(int argc, char argv[], char argv2[])
{
    char  pTypeName[4096];
    ...
    //Other pTypeName ends up populated with "Portable Network Graphics"
    //This code verifies that pTypeName is populated with what I think it is:
    char szBuff[64];
    sprintf(szBuff, pTypeName, 0);
    MessageBoxA(NULL, szBuff, szBuff, MB_OK);
    //The caption and title are "Portable Network Graphics"

    ...
    //Here, I attempt to copy the value in pTypeName to parameter 3.
    sprintf(argv2, szBuff, 0);

    return ret;
}

C＃导入

C# Import

    //I believe I have to use CharSet.Ansi because by the C++ code uses char[],
    [DllImport("FirstDll.dll", CharSet=CharSet.Ansi)]
    public static extern int xmain(int argc, string argv, ref string zzz);

C＃功能

C# Function

private void button2_Click(object sender, EventArgs e)
{
    string zzz = ""; 
    int xxx = xmain(2, @"C:\hhh.bmp", ref zzz);
    MessageBox.Show(zzz);

    //The message box displays
    //MessageBox.Show displays "IstuÈst¼ÓstÄstlÄstwÄstiÑstõÖstwÍst\
    // aÖst[ÖstÃÏst¯ÄstÐstòÄstŽÐstÅstpÅstOleMainThreadWndClass"

}

我试图通过引用传递从C＃中的参数，有C ++ DLL填充参数。尽管我已经验证该值在DLL正确的，胡言乱语被传递到C＃应用程序。

I have attempted to pass a parameter from C# by reference and have the C++ DLL populate the parameter. Even though I have verified that the value is correct in the DLL, gibberish gets passed to the C# application.

我能做些什么来写正确的字符串值，在C＃字符串？

What can I do to write the correct string value to the C# string?

推荐答案

使用的StringBuilder 来传递一个字符数组本地代码填写（见的固定长度的字符串缓冲器）

Use a StringBuilder to pass a character array that native code can fill in (see Fixed-Length String Buffers).

声明功能：

[DllImport("FirstDll.dll", CharSet=CharSet.Ansi)]
public static extern int xmain(int argc, string argv, StringBuilder argv2);

使用它：

// allocate a StringBuilder with enough space; if it is too small,
// the native code will corrupt memory
StringBuilder sb = new StringBuilder(4096);
xmain(2, @"C:\hhh.bmp", sb);
string argv2 = sb.ToString();

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