在发布版本为什么我不能返回一个char *字符串从C ++到C＃？ [英] Why can't I return a char* string from C++ to C# in a Release build?

问题描述

我试图调用从C＃以下琐碎的C函数：

  SIMPLEDLL_API为const char * ReturnString（）
{
    返回返回一个静态字符串！;
}
 

通过后的P / Invoke的声明（有或没有回报的属性，它使没有区别）：

  [的DllImport（SimpleDll）
[返回：的MarshalAs（UnmanagedType.LPStr）
公共静态外部串ReturnString（）;
 

它的工作原理，如果DLL是一个调试版本，但崩溃的发布版本（AccessViolationException）。

我打电话了十几个等简单功能，这是唯一一个出现故障（这里的其他人：）

  [的DllImport（SimpleDll）]公共静态外部INT NextInt（）;
[的DllImport（SimpleDll）]公共静态外部无效SetNextInt（INT X）;
[的DllImport（SimpleDll）]公共静态外部INT AddInts（INT A，INT B）;
[的DllImport（SimpleDll）]公共静态外部INT AddFourInts（INT A，INT B，INT C，INT D）;
[的DllImport（SimpleDll）]公共静态外部双AddDoubles（双X，双Y）;
[的DllImport（SimpleDll）]公共静态外部的IntPtr AddDoublesIndirect（REF双X，裁判双Y）;
[的DllImport（SimpleDll）] [返回：的MarshalAs（UnmanagedType.U1）
公共静态外部字符CharStringArgument（[的MarshalAs（UnmanagedType.LPStr）字符串s）;
[的DllImport（SimpleDll）] [返回：的MarshalAs（UnmanagedType.U2）
公共静态外部字符WCharStringArgument（[的MarshalAs（UnmanagedType.LPWStr）字符串s）;
[的DllImport（SimpleDll）] [返回：的MarshalAs（UnmanagedType.LPWStr）
公共静态外部串ReturnWString（）;
[的DllImport（SimpleDll）] [返回：的MarshalAs（UnmanagedType.BStr）
公共静态外部串ReturnBSTR（）;
[的DllImport（SimpleDll）]公共静态外部System.Drawing.Point MakePoint（INT X，int y）对;
[的DllImport（SimpleDll）]公共静态外部的IntPtr MakePointIndirect（INT X，int y）对;
[的DllImport（SimpleDll）]公共静态外部INT GetPointY（System.Drawing.Point P）;
[的DllImport（SimpleDll）]公共静态外部INT GetPointYIndirect（REF System.Drawing.Point PP）;
[的DllImport（SimpleDll）]公共静态外部INT SumIntegers（REF INT firstElem，诠释大小）;
 

解决方案

或者，也许尝试使用

  [的DllImport（SimpleDll）
公共静态外部的IntPtr ReturnString（）;
 

和您的通话code，使用Marshal类

 字符串RET = System.Runtime.InteropServices.Marshal.PtrToStringAnsi（PInvoke.ReturnString（））;
 

I'm attempting to call the following trivial C function from C#:

SIMPLEDLL_API const char* ReturnString()
{
    return "Returning a static string!";
}

With the following P/Invoke declaration (with or without the return attribute, it makes no difference):

[DllImport("SimpleDll")]
[return: MarshalAs(UnmanagedType.LPStr)]
public static extern string ReturnString();

It works if the DLL is a Debug build but crashes in a Release build (AccessViolationException).

I am calling over a dozen other simple functions and this is the only one that fails (here are the others:)

[DllImport("SimpleDll")] public static extern int NextInt();
[DllImport("SimpleDll")] public static extern void SetNextInt(int x);
[DllImport("SimpleDll")] public static extern int AddInts(int a, int b);
[DllImport("SimpleDll")] public static extern int AddFourInts(int a, int b, int c, int d);
[DllImport("SimpleDll")] public static extern double AddDoubles(double x, double y);
[DllImport("SimpleDll")] public static extern IntPtr AddDoublesIndirect(ref double x, ref double y);
[DllImport("SimpleDll")] [return: MarshalAs(UnmanagedType.U1)]
public static extern char CharStringArgument([MarshalAs(UnmanagedType.LPStr)]string s);
[DllImport("SimpleDll")] [return: MarshalAs(UnmanagedType.U2)]
public static extern char WCharStringArgument([MarshalAs(UnmanagedType.LPWStr)]string s);
[DllImport("SimpleDll")] [return: MarshalAs(UnmanagedType.LPWStr)]
public static extern string ReturnWString();
[DllImport("SimpleDll")] [return: MarshalAs(UnmanagedType.BStr)]
public static extern string ReturnBSTR();
[DllImport("SimpleDll")] public static extern System.Drawing.Point MakePoint(int x, int y);
[DllImport("SimpleDll")] public static extern IntPtr MakePointIndirect(int x, int y);
[DllImport("SimpleDll")] public static extern int GetPointY(System.Drawing.Point p);
[DllImport("SimpleDll")] public static extern int GetPointYIndirect(ref System.Drawing.Point pp);
[DllImport("SimpleDll")] public static extern int SumIntegers(ref int firstElem, int size);

解决方案

Or maybe try to use

[DllImport("SimpleDll")]
public static extern IntPtr ReturnString();

and in your calling code, use the Marshal Class

string ret = System.Runtime.InteropServices.Marshal.PtrToStringAnsi(PInvoke.ReturnString());

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