Readstring from BinaryReader in C# Doesn't read the first byte

Question

I'm reading a binary file using BinaryReader from System.IO in C#, however, when using ReadString it doesn't read the first byte, here is the code:

using (var b = new BinaryReader(File.Open(open.FileName, FileMode.Open)))
{
    int version = b.ReadInt32();
    int chunkID = b.ReadInt32();
    string objname = b.ReadString();
}

Is not something really hard, first it reads two ints, but the string that is supposed to return the objame is "bat", and instead it returns "at".

Does this have something to do with the two first ints i did read? Or maybe beacause there isn't a null byte between the first int and the string?

Thanks in advance.

are you sure the ints before the first string are actually 4 bytes long? Perhaps you should post the code that writes the file? — BradleyDotNET
– BradleyDotNET, Commented Aug 29, 2014 at 23:50

T_D · Accepted Answer · 2014-08-30 00:42:21Z

5

As itsme86 wrote in his answer BinaryReader.ReadString() has its own way of working and it should only be used when the created file used BinaryWriter.Write(string val).

In your case you probably have either a fixed size string where you could use BinaryReader.ReadChars(int count) or you have a null terminated string where you have to read until a 0 byte is encountered. Here is a possible extension method for reading a null terminated string:

public static string ReadNullTerminatedString(this System.IO.BinaryReader stream)
{
    string str = "";
    char ch;
    while ((int)(ch = stream.ReadChar()) != 0)
        str = str + ch;
    return str;
}

edited Aug 30, 2014 at 0:42

answered Aug 30, 2014 at 0:25

T_D

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1 Comment

Scott Chamberlain Over a year ago

Well it doesn't have to be made with BinaryWriter.Write, it just has to be a pascal string.

itsme86 · Accepted Answer · 2014-08-29 23:55:39Z

4

The string in the file should be preceded by a 7-bit encoded length. From MSDN:

Reads a string from the current stream. The string is prefixed with the length, encoded as an integer seven bits at a time.

answered Aug 29, 2014 at 23:55

itsme86

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