可以说新手使用P-INVOKE最开始的头疼就是C#和C++的字符串传递，因为这里涉及到两个问题。 第一：C#的string和C++的字符串首指针如何对应。 第二：字符串还有ANSI和UNICODE（宽字符串）之分。 本文分三部分阐述： 第一：字符串指针当输入参数， 第二：字符串指针作为返回值， 第三：字符串指针作为输入输出参数。 C++部分的测试代码很简单这里就全部贴出来了： 1#include "stdafx.h" 2#include "TestDll.h" 3#include 4#include 5#include 6 7 8 staticchar* _hello ="Hello,World!!"; 9 static TCHAR * _helloW = TEXT("Hello,World!!");1011 void __stdcall PrintString(char* hello)12{13 printf("%s\n",hello);14}1516 void __stdcall PrintStringW(TCHAR * hello)17{18 _tprintf(TEXT("%s\n"),hello);19}202122 char* __stdcall GetStringReturn()23{24return _hello;25}2627TCHAR * __stdcall GetStringReturnW()28{29return _helloW;30}313233 void __stdcall GetStringParam(char* outHello,int len)34{ //output "aaaaaaaa"35 for(int i=0; i< len -1 ;i++) outHello[i] =‘a‘;36 outHello[len -1] =‘\0‘;37}3839 void __stdcall GetStringParamW(TCHAR * outHello,int len)40{ //output "aaaaaaaa" unicode version.41 for(int i=0; i< len -1 ;i++) outHello[i] = TEXT(‘a‘);42 outHello[len -1] = TEXT(‘\0‘);43} 下面看C#如何调用。 第一：字符串指针作为输入参数，可以使用byte[] 和MarshalAs来解决。（注意四个P-INVOKE，两个ANSI版本,和两个UNICODE版本），推荐使用MarshalAs方法简单明了。 1 [DllImport("TestDll", EntryPoint ="PrintString")] 2publicstaticexternvoid PrintStringByBytes(byte[] hello); 3 4 [DllImport("TestDll", EntryPoint ="PrintString")] 5publicstaticexternvoid PrintStringByMarshal([MarshalAs(UnmanagedType.LPStr)]string hello); 6 7 [DllImport("TestDll", EntryPoint ="PrintStringW")] 8publicstaticexternvoid PrintStringByBytesW(byte[] hello); 910 [DllImport("TestDll", EntryPoint ="PrintStringW")]11publicstaticexternvoid PrintStringByMarshalW([MarshalAs(UnmanagedType.LPWStr)]string hello);121314publicvoid Run()15 {16 PrintStringByBytes(Encoding.ASCII.GetBytes("use byte[]"));17 PrintStringByMarshal("use MarshalAs");18 PrintStringByBytesW(Encoding.Unicode.GetBytes("use byte[]"));19 PrintStringByMarshalW("use MarshalAs");20} 第二：字符串指针作为返回值，和上面一样也有两种声明方法，同样也包含两个版本。注意：Marshal.PtrToStringAnsi()函数的使用，把字符串指针转变为C#的string.推荐使用MarshalAs方法简单明了。 1 [DllImport("TestDll", EntryPoint ="GetStringReturn")] 2publicstaticextern IntPtr GetStringReturnByBytes(); 3 4 [DllImport("TestDll", EntryPoint ="GetStringReturn")] 5 [return:MarshalAs(UnmanagedType.LPStr)] 6publicstaticexternstring GetStringReturnByMarshal(); 7 8 [DllImport("TestDll", EntryPoint ="GetStringReturnW")] 9publicstaticextern IntPtr GetStringReturnByBytesW();1011 [DllImport("TestDll", EntryPoint ="GetStringReturnW")]12 [return: MarshalAs(UnmanagedType.LPWStr)]13publicstaticexternstring GetStringReturnByMarshalW();141516publicvoid Run()17 { //Marshal.PtrToStringAuto(GetStringReturnByBytes()); 自动判断类型不错。18 Console.WriteLine(Marshal.PtrToStringAnsi(GetStringReturnByBytes()));19 Console.WriteLine(GetStringReturnByMarshal());20 Console.WriteLine(Marshal.PtrToStringUni(GetStringReturnByBytesW()));21 Console.WriteLine(GetStringReturnByMarshalW());22} 第三：字符串指针作为输入输出参数时，因为要求有固定的容量，所以这里使用的是StringBuilder，大家仔细看了，当然也有byte[]版本。这个看大家喜欢那个版本就是用那个. 1 [DllImport("TestDll", EntryPoint ="GetStringParam")] 2publicstaticexternvoid GetStringParamByBytes(byte[] outHello, int len); 3 4 [DllImport("TestDll", EntryPoint ="GetStringParam")] 5publicstaticexternvoid GetStringParamByMarshal([Out, MarshalAs(UnmanagedType.LPStr)]StringBuilder outHello, int len); 6 7 [DllImport("TestDll", EntryPoint ="GetStringParamW")] 8publicstaticexternvoid GetStringParamByBytesW(byte[] outHello, int len); 910 [DllImport("TestDll", EntryPoint ="GetStringParamW")]11publicstaticexternvoid GetStringParamByMarshalW([Out, MarshalAs(UnmanagedType.LPWStr)]StringBuilder outHello, int len);121314publicbyte[] _outHello =newbyte[10];15publicbyte[] _outHelloW =newbyte[20];16public StringBuilder _builder =new StringBuilder(10); //很重要设定string的容量。17 18publicvoid Run()19 {20//21 GetStringParamByBytes(_outHello, _outHello.Length);22 GetStringParamByMarshal(_builder, _builder.Capacity);23 GetStringParamByBytesW(_outHelloW, _outHelloW.Length /2);24 GetStringParamByMarshalW(_builder, _builder.Capacity);2526//27 Console.WriteLine(Encoding.ASCII.GetString(_outHello));28 Console.WriteLine(_builder.ToString());29 Console.WriteLine(Encoding.Unicode.GetString(_outHelloW));30 Console.WriteLine(_builder.ToString());31}

C# C++ 字符串传递