C#•5mo ago

Trying to read from a binary file

New to c#, trying to validate a username and password from a binary file, but getting the issue 'Too many bytes in what should have been a 7-bit encoded integer. Not too familiar with binary readers and writers, can anyone help?

64 Replies

Pobiega•5mo ago

That some funky code there especially since you rewind the stream before trying to read, in a loop what is that loop and that rewind doing there?

RuarasSwiftArrow•5mo ago

I'm honestly not sure, haven't been taught how to do this yet and have little understanding of how it all works so this is cobbled together from the little I do know and various stack overflow questions 😭

Jimmacle•5mo ago

is there a reason you're using a binary reader?

RuarasSwiftArrow•5mo ago

as part of the assignment we have to read and write from a binary file

Pobiega•5mo ago

alright so just walk us through exactly what you are trying to do here

Jimmacle•5mo ago

yeah readstring expects the data to be in a specific format namely length-prefixed with 7 bit characters

Pobiega•5mo ago

How was this binary file made? BinaryWriter?

RuarasSwiftArrow•5mo ago

So in the binary file there are user details, username, password, then a few others. I want to take user input, which is fine, and then check it against the username and password stored in the binary file. The username written to the binary file was created by a binary writer writing a string, and the password by a binary writer writing an int (I hashed the password) oh yeah i forgot there are multiple users details in a single file so I need to loop through them all

Pobiega•5mo ago

can you show the write code? so we know the format of the reading

RuarasSwiftArrow•5mo ago

player is a class, Username is string and Password is an int

Pobiega•5mo ago

Mhm... and you just... append to this bin file? no lead int that tells you how many players the file contains?

RuarasSwiftArrow•5mo ago

yeah, this was the code we were given to do this

Pobiega•5mo ago

okay okay, thats fine a little less safe, but still doable I'll begin with posting a little snippet of code

private static void Read()
{
    var fs = File.OpenRead("data.bin");
    using var br = new BinaryReader(fs);

    // str, int, str
    Console.WriteLine(br.ReadString());
    Console.WriteLine(br.ReadInt32());
    Console.WriteLine(br.ReadString());
    
    br.Close();
}

private static void Write()
{
    var fs = File.OpenWrite("data.bin");
    using var bw = new BinaryWriter(fs);

    // str, int, str
    bw.Write("I am a test string");
    bw.Write(512);
    bw.Write("Second string");

    bw.Close();
}

private static void Read()
{
    var fs = File.OpenRead("data.bin");
    using var br = new BinaryReader(fs);

    // str, int, str
    Console.WriteLine(br.ReadString());
    Console.WriteLine(br.ReadInt32());
    Console.WriteLine(br.ReadString());
    
    br.Close();
}

private static void Write()
{
    var fs = File.OpenWrite("data.bin");
    using var bw = new BinaryWriter(fs);

    // str, int, str
    bw.Write("I am a test string");
    bw.Write(512);
    bw.Write("Second string");

    bw.Close();
}

note how we must write and read in the exact same order, with the exact same types and the exact same count of things binary wont let you skip around in the file, you need to know exactly what is where so if you have an unknown amount of players, you'll need to read until the stream reaches its end, and you must read an entire full "player" struct at a time

RuarasSwiftArrow•5mo ago

right I think I'm understanding now, I use the read to iterate through what is in the file, and check against it, then move to the next line, and I need to read everything on a line before going to the next one

Pobiega•5mo ago

.. what?

RuarasSwiftArrow•5mo ago

maybe I'm not understanding give me a minute to see thank you so much though this is helping a lot

Pobiega•5mo ago

write will uh... write to the file :p you dont wanna write when reading.

RuarasSwiftArrow•5mo ago

I meant to type read sorry tired ahaha changed it now, am i on the right tracks?

Pobiega•5mo ago

something along those lines but there is no concept of "lines" in a binary file its just a stream of binary data BUT, since we know the structure of the data inside that stream, as long as we read one "block" at a time, we're good

RuarasSwiftArrow•5mo ago

I think i got it now, I'll probably be back here in 5 minutes to ask for me help however haha thank you

RuarasSwiftArrow•5mo ago

I'm still getting this original issue

Pobiega•5mo ago

hm, your file must be malformed I'd recommend re-generating it

RuarasSwiftArrow•5mo ago

ok I'll give that a go thanks

Pobiega•5mo ago

ReadString reads a number from the file, which is how many chars to read for the string, then it reads that amount of chars. If that fails, you get this error it most likely means your binary file didnt start with a string, or was somehow modified after it was created binary is very hard to work with for this reason, and you cant just open the file in a text editor like with json etc

RuarasSwiftArrow•5mo ago

that sorted one issue and uncovered another

RuarasSwiftArrow•5mo ago

ah i opened it a few times with notepad that must have triggered it

Pobiega•5mo ago

that might be it yeah hm, why would it try reading beyond the end of the stream... do you have any loops or stuff going here? also when you write, you dont write any ints you just write 5 strings

Pobiega•5mo ago

at least thats what you showed us before

RuarasSwiftArrow•5mo ago

player.Password is an integer

Pobiega•5mo ago

ah okay

RuarasSwiftArrow•5mo ago

because I hash the password yeah I have a for loop going around it here one sec

Pobiega•5mo ago

show me da loop.

RuarasSwiftArrow•5mo ago

Pobiega•5mo ago

uuh what

RuarasSwiftArrow•5mo ago

just one that should only run once to test

Pobiega•5mo ago

oh there are many things wrong here you need to open the stream and reader before the loop and close the reader AFTER the loop also, here is a more appropriate "end of line" check: while (br.BaseStream.Position < br.BaseStream.Length)

RuarasSwiftArrow•5mo ago

the "end of line" check is for the for loop yeah?

Pobiega•5mo ago

RuarasSwiftArrow•5mo ago

yeah im still getting the same issue

RuarasSwiftArrow•5mo ago

Pobiega•5mo ago

and you're sure users.bin is fine now?

RuarasSwiftArrow•5mo ago

havent touched it since

Pobiega•5mo ago

hm cause it all works fine on my end

RuarasSwiftArrow•5mo ago

remade it, made it by saving a blank file from notepad as a .bin in case that matters

Pobiega•5mo ago

oh no no delete the file don't ever open binary files with a text editor

RuarasSwiftArrow•5mo ago

how do i manually generate one then?

Pobiega•5mo ago

with your "write" program/method

RuarasSwiftArrow•5mo ago

yeah so deleted it and let it create through the program and error still occurs

Pobiega•5mo ago

hm might be time to install a hex editor and inspect your file

Jimmacle•5mo ago

iirc vscode has one built in, if not there's an extension

Pobiega•5mo ago

not built in, but defo extensions I personally use ImHex

RuarasSwiftArrow•5mo ago

essentially turning it on and off again to see if it sorts itself it didnt, just to check, it always accesses the file withing the project right?

Pobiega•5mo ago

and you are sure you are writing 1 string 1 int32 3 more strings, per user? well, the file in your bin/net8.0/ folder if its generated and read at runtime

RuarasSwiftArrow•5mo ago

I'm using 5.0 for reference not by choice

Pobiega•5mo ago

thats fine but yeah, the file will be at YourProjectHere\bin\Debug\net5.0\Users.bin

RuarasSwiftArrow•5mo ago

yeah just searched for writers and thats all I could see wait i might be an idiot

Pobiega•5mo ago

these are words all programmers are very familiar with

RuarasSwiftArrow•5mo ago

damn I'm working on an older version where my username is stored as an int (I hashed it too for some reason), changed it recently but forgot to use that one 😭 let me run it now and see if it works

Pobiega•5mo ago

yeah that'd majorly fuck this up

RuarasSwiftArrow•5mo ago

it works! thank you so much, sorry for wasting your time at the end there

Pobiega•5mo ago

can highly recommend imhex btw. I taught it to recognize a C# string and then my "player" structure

Pobiega•5mo ago

Gaming

Programming

Trying to read from a binary file