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Preferred way to parse a custom binary flat file?

I have a flat file generated by program C. Each entry in the file consists of a fixed-length header followed by data. The header contains a field indicating the size of the following data. My ultimate goal is to write a C # /. NET program to request this flat file, so I'm looking for the most efficient way to read the file using C #.

I am having trouble finding the .NET equivalent of line 7 in the following code. As far as I can tell, I need to issue several readings (one for each header field using BinaryReader), and then release one read to get the data following the header. I am trying to learn how to analyze records in two read operations (one is read to get a fixed-length header, and the second is read to get the following data).

This is the C code I'm trying to duplicate using C # /. NET:

struct header header; /* 1-byte aligned structure (48 bytes) */
char *data;

FILE* fp = fopen("flatfile", "r");
while (!feof(fp))
{
  fread(&header, 48, 1, fp);
  /* Read header.length number of bytes to get the data. */
  data = (char*)malloc(header.length);
  fread(data, header.length, 1, fp);
  /* Do stuff... */
  free(data);
}

This is the C header structure:

struct header
{
    char  id[2];
    char  toname[12];
    char  fromname[12];
    char  routeto[6];
    char  routefrom[6];
    char  flag1;
    char  flag2;
    char  flag3;
    char  flag4;
    char  cycl[4];
    unsigned short len;
};

I came up with this C # object to represent the C header:

[StructLayout(LayoutKind.Sequential, Pack = 1, CharSet = CharSet.Ansi, Size = 48)]
class RouterHeader
{
    [MarshalAs(UnmanagedType.ByValArray, SizeConst = 2)]
    char[] Type;

    [MarshalAs(UnmanagedType.ByValArray, SizeConst = 12)]
    char[] To;

    [MarshalAs(UnmanagedType.ByValArray, SizeConst = 12)]
    char[] From;

    [MarshalAs(UnmanagedType.ByValArray, SizeConst = 6)]
    char[] RouteTo;

    [MarshalAs(UnmanagedType.ByValArray, SizeConst = 6)]
    char[] RouteFrom;

    [MarshalAs(UnmanagedType.ByValArray, SizeConst = 4)]
    char[] Flags;

    [MarshalAs(UnmanagedType.ByValArray, SizeConst = 4)]
    char[] Cycle;

    UInt16 Length;
}
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5 answers

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My desire was to read the data in an array and then collect the data object accordingly, using shifts and adding words, words, etc. to the words. I have some utility classes for handling such things.

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