C语言的des加密函数没有返回值，如何封装为DLL供C#调用

[fanshow]

头文件中定义了：
extern void deskey(unsigned char *, short);

在C编译器中调试如下，并通过
char str[]="tianshan";
deskey("0123456789abcdef",EN0);//第一个参数是key 第二个是字定义的加密解密的宏
des(str, str);
puts("加密后");
puts(str);


puts("解密后");
deskey("0123456789abcdef",DE1);
des(str, str);
puts(str);


des（）没有返回值，如何封装供C#调用呢？ 调用怎么接收str呢?

[fanshow]

des(str, str); 中后面一个str是加密后的数据，怎么返回？

[jinru2560]

unsigned char * 就是返回值

[jointan]

extern "C" _declspec(dllexport) void __stdcall DES( OUT LPSTR lpszBuffer,IN LPCSTR lpszSource);

[fanshow]

extern void des(unsigned char *, unsigned char *);

[xuld]

[DllImport("_____.dll")]
extern static void deskey(out string value, short i);

[fanshow]

out 恩，我试验一下

[fanshow]

头文件：

extern "C" __declspec(dllexport) void deskey(unsigned char *, short);
extern "C" __declspec(dllexport) void des(unsigned char *, unsigned char *);//后一个参数是加密后的数据

C#中
[DllImport("wdll.dll", EntryPoint = "deskey", CharSet = CharSet.Auto, CallingConvention = CallingConvention.StdCall)]

public static extern void deskey(string key, short mode);


[DllImport("wdll.dll", EntryPoint = "des", CharSet = CharSet.Auto, CallingConvention = CallingConvention.StdCall)]

public static extern void des(string str, out string value); 　//这里怎么报错呢

[jointan]

        [DllImport("wdll.dll", EntryPoint = "des", CharSet = CharSet.Ansi )]
        public static extern void des(string str, StringBuilder  value);

        public static string DES(string str)
        {
            StringBuilder sb = new StringBuilder(256);
            des(str, sb);
            return sb.ToString();
        }

[fanshow]

神啊 jointan 太厉害了