Reading and writing unmanged structs from binary files
I still remember one of the first tasks during my internship (At a software shop that still used Visual Studio 6 as development environment) last year: Develop a GUI application using .Net that allows the user to manipulate data stored in a binary file which was generated by c/c++ program. As a newcomer to C# programming i just couldn’t find the right attributes to Marshal the following structs:
struct test1 {
char name[9];
int score;
};
struct test2 {
test1 items[10];
}
char name[9];
int score;
};
struct test2 {
test1 items[10];
}
After a couple of days they wanted me to deliver a product, so i decided to stop experimenting and wrote the application in C++ (Example). Since i don’t like unanswered questions, i decided to give it another try this afternoon… It didn’t take long to come up with the following:
[StructLayout(LayoutKind.Sequential, CharSet=CharSet.Ansi, Pack=4)]
struct Test1
{
[MarshalAs(UnmanagedType.ByValTStr, SizeConst=9)]
public string Name;
public int Score;
}
[StructLayout(LayoutKind.Sequential, CharSet=CharSet.Ansi, Pack=4)]
struct Test2
{
[MarshalAs(UnmanagedType.ByValArray, SizeConst=10)]
public Test1[] Items;
}
static object Read(Stream stream, Type t)
{
byte[] buffer = new byte[Marshal.SizeOf(t)];
for (int read = 0; read < buffer.Length; read += stream.Read(buffer, read, buffer.Length)) ;
GCHandle gcHandle = GCHandle.Alloc(buffer, GCHandleType.Pinned);
object o = Marshal.PtrToStructure(gcHandle.AddrOfPinnedObject(), t);
gcHandle.Free();
return o;
}
static void Write(Stream stream, object o)
{
byte[] buffer = new byte[Marshal.SizeOf(o.GetType())];
GCHandle gcHandle = GCHandle.Alloc(buffer, GCHandleType.Pinned);
Marshal.StructureToPtr(o, gcHandle.AddrOfPinnedObject(), true);
stream.Write(buffer, 0, buffer.Length);
gcHandle.Free();
}
static void Main(string[] args)
{
Test1 test1 = new Test1();
test1.Name = "timvw";
test1.Score = 100;
using (FileStream fileStream = new FileStream(@"c:\test.dat", FileMode.OpenOrCreate))
{
Write(fileStream, test1);
fileStream.Seek(0, SeekOrigin.Begin);
Test1 test2 = (Test1) Read(fileStream, typeof(Test1));
Console.WriteLine("Name: {0} Score: {1}", test2.Name, test2.Score);
}
Console.Write("{0}Press any key to continue…", Environment.NewLine);
Console.ReadKey();
}