C# 调用C++ dll 返回char*调用方式（StringBuilder乱码）

using System;
using System.Collections.Generic;
using System.Linq;
using System.Runtime.InteropServices;
using System.Text;
using System.Threading.Tasks;

namespace DotNet_Use_C_Demo
{
    public class TestCMethodHelper
    {
        [DllImport("CDLLDemo.dll", CallingConvention = CallingConvention.Cdecl, CharSet = CharSet.Auto)]
        private static extern int ParseBaliseMsg2(string msg, string rmsg, ref byte memory);

        [DllImport("CDLLDemo.dll", CallingConvention = CallingConvention.Cdecl, CharSet = CharSet.Auto)]
        private static extern IntPtr ParseBaliseMsg3(string msg, string rmsg, ref int rInt);

        [DllImport("CDLLDemo.dll", CallingConvention = CallingConvention.Cdecl, CharSet = CharSet.Auto)]
        private static extern IntPtr ParseBaliseMsg4(string msg, string rmsg, [MarshalAs(UnmanagedType.LPStr)]StringBuilder t);

        [DllImport("CDLLDemo.dll", CallingConvention = CallingConvention.Cdecl, CharSet = CharSet.Auto)]
        private static extern IntPtr ParseBaliseMsg5([MarshalAs(UnmanagedType.LPStr)]StringBuilder msg, string rmsg, [MarshalAs(UnmanagedType.LPStr)]StringBuilder t);

        [DllImport("CDLLDemo.dll", EntryPoint = "strcpyTest", CallingConvention = CallingConvention.Cdecl/*, CallingConvention = CallingConvention.Cdecl*/)]
        public static extern IntPtr strcpyTest(ref byte destA, string sourA);

        public static void TestMethod()
        {
            Byte[] bPara = new Byte[100];    //新建字节数组
            var r2 = ParseBaliseMsg2("abcd", "", ref bPara[0]);
            string strGet = System.Text.Encoding.Default.GetString(bPara, 0, bPara.Length);    //将字节数组转换为字符串
            Console.WriteLine("返回值：" + r2);
            Console.WriteLine("传出值：" + strGet);
            Console.WriteLine("***************************************************");

            int retResult = 0;
            IntPtr pRet = ParseBaliseMsg3("1234", "", ref retResult);
            string strRet = Marshal.PtrToStringAnsi(pRet);
            Console.WriteLine("返回值：" + strRet);
            Console.WriteLine("传出值：" + retResult);
            Console.WriteLine("***************************************************");

            //StringBuilder方式
            StringBuilder sb = new StringBuilder();
            var r4 = ParseBaliseMsg4("abcd", "", sb);
            Console.WriteLine("返回值：" + r4);
            Console.WriteLine("传出值：" + sb.ToString());
            Console.WriteLine("***************************************************");

            StringBuilder sb5 = new StringBuilder();
            StringBuilder sb5E_para = new StringBuilder();
            sb5E_para.Append("abcdedf123456");
            var r5 = ParseBaliseMsg5(sb5E_para, "", sb5);
            Console.WriteLine("返回值：" + r5);
            Console.WriteLine("传出值：" + sb5.ToString());
        }

        public static void CpyTest()
        {
            string strSour = "测试调用C++ dll";

            Byte[] bPara = new Byte[100];    //新建字节数组

            IntPtr pRet = strcpyTest(ref bPara[0], strSour);
            string strGet = System.Text.Encoding.Default.GetString(bPara, 0, bPara.Length);    //将字节数组转换为字符串
            string strRet = Marshal.PtrToStringAnsi(pRet);

            Console.WriteLine("源字符串：");
            Console.WriteLine(strSour);

            Console.WriteLine("传出值：");
            Console.WriteLine(strGet);

            Console.WriteLine("返回值：");
            Console.WriteLine(strRet);
        }
    }
}

1.用StringBuilder接收Char*参数 需要定义为[MarshalAs(UnmanagedType.LPStr)]StringBuilder，否则就是乱码。

2.用ref byte memory接收Char*参数  不能使用ref IntPtr方式接收，否则返回值一直为空。

3.使用返回值Char*  直接使用IntPtr方式接收即可。