转换为.net:Native Utf-8 < - >托管字符串

Question

我创建了这两个方法来将Native utf-8字符串(char*)转换为托管字符串,反之亦然.以下代码完成了这项工作:

public IntPtr NativeUtf8FromString(string managedString)
{
    byte[] buffer = Encoding.UTF8.GetBytes(managedString); // not null terminated
    Array.Resize(ref buffer, buffer.Length + 1);
    buffer[buffer.Length - 1] = 0; // terminating 0
    IntPtr nativeUtf8 = Marshal.AllocHGlobal(buffer.Length);
    Marshal.Copy(buffer, 0, nativeUtf8, buffer.Length);
    return nativeUtf8;
}

string StringFromNativeUtf8(IntPtr nativeUtf8)
{
    int size = 0;
    byte[] buffer = {};
    do
    {
        ++size;
        Array.Resize(ref buffer, size);
        Marshal.Copy(nativeUtf8, buffer, 0, size);
    } while (buffer[size - 1] != 0); // till 0 termination found

    if (1 == size)
    {
        return ""; // empty string
    }

    Array.Resize(ref buffer, size - 1); // remove terminating 0
    return Encoding.UTF8.GetString(buffer);
}

虽然NativeUtf8FromString没问题,但StringFromNativeUtf8是一个混乱,但我可以运行唯一安全的代码.使用不安全的代码我可以使用字节*但我不想要不安全的代码.有没有其他人可以想到我不必为每个包含的字节复制字符串以找到0终止.

---

我只是在这里添加unsave代码:

public unsafe string StringFromNativeUtf8(IntPtr nativeUtf8)
{
    byte* bytes = (byte*)nativeUtf8.ToPointer();
    int size = 0;
    while (bytes[size] != 0)
    {
        ++size;
    }
    byte[] buffer = new byte[size];
    Marshal.Copy((IntPtr)nativeUtf8, buffer, 0, size);
    return Encoding.UTF8.GetString(buffer);
}

如你所见,它不丑,只需要不安全.

Answer 1

只需执行strlen()执行的完全相同的操作.考虑保持缓冲区,代码确实产生垃圾匆忙.

    public static IntPtr NativeUtf8FromString(string managedString) {
        int len = Encoding.UTF8.GetByteCount(managedString);
        byte[] buffer = new byte[len + 1];
        Encoding.UTF8.GetBytes(managedString, 0, managedString.Length, buffer, 0);
        IntPtr nativeUtf8 = Marshal.AllocHGlobal(buffer.Length);
        Marshal.Copy(buffer, 0, nativeUtf8, buffer.Length);
        return nativeUtf8;
    }

    public static string StringFromNativeUtf8(IntPtr nativeUtf8) {
        int len = 0;
        while (Marshal.ReadByte(nativeUtf8, len) != 0) ++len;
        byte[] buffer = new byte[len];
        Marshal.Copy(nativeUtf8, buffer, 0, buffer.Length);
        return Encoding.UTF8.GetString(buffer);
    }

Answer 2

.NET 5（.NET Standard 2.1）中添加了Marshal.PtrToStringUTF8和Marshal.StringToCoTaskMemUTF8

Answer 3

比 Hans 的解决方案略快（减少 1 个缓冲区副本）：

private unsafe IntPtr AllocConvertManagedStringToNativeUtf8(string input) {
    fixed (char* pInput = input) {
        var len = Encoding.UTF8.GetByteCount(pInput, input.Length);
        var pResult = (byte*)Marshal.AllocHGlobal(len + 1).ToPointer();
        var bytesWritten = Encoding.UTF8.GetBytes(pInput, input.Length, pResult, len);
        Trace.Assert(len == bytesWritten);
        pResult[len] = 0;
        return (IntPtr)pResult;
    }
}

private unsafe string MarshalNativeUtf8ToManagedString(IntPtr pStringUtf8)
    => MarshalNativeUtf8ToManagedString((byte*)pStringUtf8);

private unsafe string MarshalNativeUtf8ToManagedString(byte* pStringUtf8) {
    var len = 0;
    while (pStringUtf8[len] != 0) len++;
    return Encoding.UTF8.GetString(pStringUtf8, len);
}

这是我对字符串进行往返的演示：

var input = "Hello, World!";
var native = AllocConvertManagedStringToNativeUtf8(input);
var copy = MarshalNativeUtf8ToManagedString(native);
Marshal.FreeHGlobal(native); // don't leak unmanaged memory!
Trace.Assert(input == copy); // prove they're equal!