c#调用c语言dll,形参有char*

c#调用c语言dll,形参有char*，无法获得char*内容。但是在c++中调用dll无问题。说明dll正确，C#中代码有问题。

直接解决方法：未解决，dll没问题，就是调用后存储在webtoken中读取有问题，求大神告知解决方法：

变相解决方法：修改dll文件，将形参char*作为返回值char*返回。

原先的c函数声明：

#ifndef _DLLMAIN_H  
#define _DLLMAIN_H  
#ifndef        DLL_EXPORT  
#define _LIBAPI __declspec(dllexport)  
#else  
#define _LIBAPI __declspec(dllimport)  
#endif  
#ifdef __cplusplus
extern "C" {
#endif
_LIBAPI void getWebToken(const char* appkey, const char* counter, char* webtoken)
#ifdef __cplusplus
}
#endif
#endif /* _DLL_H_ */

原先的调用方式：无法获得webtoken中的字符串。

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
using System.Runtime.InteropServices;
namespace WindowsFormsApplication2
{
    public partial class Form1 : Form
    {
        [DllImport("omp_sec_dll.dll", EntryPoint = "getWebToken", CallingConvention = CallingConvention.Cdecl)]

        public static extern void getWebToken1(string appkey, string counter, ref IntPtr webtoken);  

        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            string appkey = "123456781111";
            string counter = "876543211111";
            string txt = "testttttttttttt";
            IntPtr webtoken = Marshal.StringToHGlobalAnsi(txt);
            string temp = Marshal.PtrToStringAnsi(webtoken);
            getWebToken1(appkey, counter, ref webtoken);
            string result = Marshal.PtrToStringAnsi(webtoken);
            MessageBox.Show(result);
        }
    }
}

修改后的C函数声明：

#ifndef _DLLMAIN_H  
#define _DLLMAIN_H  
#ifndef        DLL_EXPORT  
#define _LIBAPI __declspec(dllexport)  
#else  
#define _LIBAPI __declspec(dllimport)  
#endif  
#ifdef __cplusplus
extern "C" {
#endif
_LIBAPI char* getWebToken(char* appkey, const char* counter);
#ifdef __cplusplus
}
#endif
#endif /* _DLL_H_ */

变相解决后的调用方式：修改dll函数返回值为char*，修改appkey为IntPtr，此时能正常获得char*。

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
using System.Runtime.InteropServices;//add

namespace TestGetWebToken
{
    public partial class Form1 : Form
    {
        [DllImport("omp_sec_dll.dll", EntryPoint = "getWebToken", CallingConvention = CallingConvention.Cdecl)] //add

        public static extern IntPtr getWebToken1(IntPtr appkey, string counter);  //add

        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            IntPtr appkey = Marshal.StringToHGlobalAuto("123456781111");
            string counter = "876543211111";
            IntPtr tmp = Java_com_cmcc_omp_WebSecuritySubassembly_getWebToken1(appkey, counter);
            string result = Marshal.PtrToStringAnsi(tmp);
            MessageBox.Show(result);
        }
    }
}

总结：

1. const char* 直接换成string

2. char*做形参或返回值，需要换成IntPtr

3. char*做形参并想要获取char*内容，使用ref IntPtr无用。只能将该char*改为返回值获得。