c# - char** DllImport 失败

Question

我想 DllImport 以下功能。然而，“ret”返回 true，但我的字符串数组似乎是空的，所以我想我可能需要一些编码(marshal)处理。欢迎任何提示!提前致谢:)

C 函数:

bool getBootLog(char **a1);

以下代码用于测试，无法正常运行。

DllImport:

[DllImport("ext.dll")]
public static extern bool getBootLog(string[] bootLog);

当前代码:

        string[] bootLog = new string[1024 * 1024];
        bool ret = getBootLog(bootLog);

        foreach (string s in bootLog)
        {
            Debug.WriteLine(s);
        }

2 次尝试无效:

var ptr = Marshal.AllocHGlobal(Marshal.SizeOf(typeof(IntPtr)));
try
{
    getBootLog(out ptr);
    var deref1 = (string)Marshal.PtrToStringAnsi(ptr);
    Debug.WriteLine(deref1);
}
finally
{
    Marshal.FreeHGlobal(ptr);
}

var ptr2 = Marshal.AllocHGlobal(Marshal.SizeOf(typeof(IntPtr)));
try
{
    getBootLog(out ptr2);
    var deref1 = (IntPtr)Marshal.PtrToStructure(ptr2, typeof(IntPtr));
    var deref2 = (string[])Marshal.PtrToStructure(deref1, typeof(string[]));
    Debug.WriteLine(deref2);
}
finally
{
    Marshal.FreeHGlobal(ptr2);
}

莫森的想法:

[DllImport("Ext.dll")]
public static extern bool getBootLog(StringBuilder bootLog);

try
{
    int bufferSize = 50;
    StringBuilder bootLog = new StringBuilder(" ", bufferSize);
    Debug.WriteLine("Prepared bootLog...");
    getBootLog(bootLog);
    Debug.WriteLine("Bootlog length: " + bootLog.Length);
    string realString = bootLog.ToString();
    Debug.WriteLine("Bootlog: " + realString);
}
catch(Exception ex)
{
    Debug.WriteLine("Xception: " + ex.ToString());
}

结果:

Prepared bootLog... Bootlog length: 0 Bootlog:

Answer 1

修改声明:

[DllImport("ext.dll", CharSet = CharSet.Ansi)]
public static extern bool getBootLog(ref IntPtr bootLogPtr);

代码编辑版本中尝试的行看起来不正确。

var ptr = Marshal.AllocHGlobal(Marshal.SizeOf(typeof(IntPtr)));

确实，应该指定缓冲区的大小。

var ptr = Marshal.AllocHGlobal(100); // Set it to 100 bytes, maximum!

将长度写入 ptr，作为其 C 风格的空终止字符串。

Marshal.WriteByte(ptr, 100, 0);

然后调用将在我脑海中出现的调用:

IntPtr ptrBuf = ptr;
getBootLog(ref ptrBuf);

通过ptrBuf将缓冲区的内容复制到字符串变量中:

string sBootLog = Marshal.PtrToStringAnsi(ptrBuf);

清理非托管内存内容:

Marshal.FreeHGlobal(ptr);