c++ DLL和c#之间传递字符串

c++代码

extern "C" _declspec(dllexport) bool get(char*& strPorts)
{
    string str = "Hello";
    int length = str.size() + 1;
    strPorts = newchar[length];
    strcpy_s(strPorts, length, str.c_str());
    return true;
}
extern "C" _declspec(dllexport) bool set(char* str)
{
    cout << str << endl;
    return true;
}

c#代码

    [DllImport("My.dll")]
    public static extern bool get(out IntPtr pstrPorts);
    [DllImport("My.dll")]
    public static extern bool set(string strPorts);
    //调用
    IntPtr pStr;
    get(out pStr);
    System.Console.WriteLine(Marshal.PtrToStringAnsi(pStr));

    string str="Hello";
    set(str);

因为set里面传递的指针是空的，需要dll来new，百度了好久才找到解决方案。