问题描述
我试图来一补结构（不必是一个实际的结构），从一个byte []加载的数据。
I'm trying to fill a structure (does not have to be an actual struct), with data loaded from a byte[].
有许多不同在字节[]数据结构，其中之一是一个字符串，它被声明为：
There are many different data structures in the byte[], one of them is a string, which is declared as:
UInt16 stringLenght
byte[stringLenght] zeroTerminatedString
我的C语言，这可以通过声明一个固定大小的结构处理，以及，而不是包含实际字符串结构，做一个字符串指针
I 'c' language this could be handled by declaring a fixed size struct, and instead of a the struct containing the actual string, make a pointer to the string.
是这样的：
UInt16 stringLength
char* zeroTerminatedString
有一（SMART）的方式做在C＃中类似的东西？我的意思是从文件/内存加载的二进制数据，并将其填充到一个结构？
Is there a (smart) way to do something similar in c#? I mean loading binary data from a file/memory and filling it into a structure?
问候
雅各布Justesen
RegardsJakob Justesen
推荐答案
这不是如果文件中的记录包含一个字符串，你会怎样声明它C.那么你声明的结构相似：
That's not how you'd declare it in C. If the record in the file contains a string then you'd declare the structure similar to:
struct Example {
int mumble; // Anything, not necessarily a string length
char text[42];
// etc...
};
等价的C＃的声明看起来像：
The equivalent C# declaration would look like:
[StructLayout(LayoutKind.Sequential, Pack = 1, CharSet = CharSet.Ansi)]
private struct Example {
public int mumble;
[MarshalAs(UnmanagedType.ByValTStr, SizeConst = 42)]
public string text;
// etc...
}
您会正常使用BinaryReader读取数据。但它不能直接处理这样的字符串，你要读他们作为一个byte []，做串转换自己。您也可以不走声明语法的优势，你必须写为结构的每个成员的电话。
You'd normally use BinaryReader to read the data. But it cannot handle strings like this directly, you have to read them as a byte[] and do the string conversion yourself. You also cannot take advantage of the declarative syntax, you have to write a call for each individual member of the struct.
有对一个解决办法，Marshal类已经知道如何将非托管的结构转换为管理那些与PtrToStructure（）方法。这里有一个通用的实现，它可以用于任何类型的blittable。两个版本，一个静态的，从一个byte []，并且进行了优化，从流反复读一个实例方法读取。你会使用一个FileStream或使用的MemoryStream一个
There's a workaround for that, the Marshal class already knows how to convert unmanaged structures to managed ones with the PtrToStructure() method. Here's a generic implementation, it works for any blittable type. Two versions, a static one that reads from a byte[] and an instance method that was optimized to repeatedly read from a stream. You'd use a FileStream or MemoryStream with that one.
using System;
using System.IO;
using System.Runtime.InteropServices;
class StructTranslator {
public static bool Read<T>(byte[] buffer, int index, ref T retval) {
if (index == buffer.Length) return false;
int size = Marshal.SizeOf(typeof(T));
if (index + size > buffer.Length) throw new IndexOutOfRangeException();
var handle = GCHandle.Alloc(buffer, GCHandleType.Pinned);
try {
IntPtr addr = (IntPtr)((long)handle.AddrOfPinnedObject() + index);
retval = (T)Marshal.PtrToStructure(addr, typeof(T));
}
finally {
handle.Free();
}
return true;
}
public bool Read<T>(Stream stream, ref T retval) {
int size = Marshal.SizeOf(typeof(T));
if (buffer == null || size > buffer.Length) buffer = new byte[size];
int len = stream.Read(buffer, 0, size);
if (len == 0) return false;
if (len != size) throw new EndOfStreamException();
var handle = GCHandle.Alloc(buffer, GCHandleType.Pinned);
try {
retval = (T)Marshal.PtrToStructure(handle.AddrOfPinnedObject(), typeof(T));
}
finally {
handle.Free();
}
return true;
}
private byte[] buffer;
}
未经检验的，希望它的作品。
Untested, hope it works.
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