On 19/04/13 20:11, ballsystemlord wrote: > I'm a beginner am and wondering how to open a binary file, read a certain > amount of bytes from it and then write the data after proccesssing it into a > different file. I would like to use several threads and to make the data > transferable from on computer to another. > I've read the docs and am still unsure how to make my threads read the data > and replace it in the same order that they took it up from the original. > Further I have no idea how to write down part of an int. First, this isn't a doubt about gcc, but about programming (gcc can compile different languages, as you didn't specify, you are probably interested in doing it in C). Second, there's no need to use several threads for this. You won't gain anything. You could annotate each thread with the piece of the file they should read and then write, but a single-thread program will work equally well, while being simpler. Third, making the data transferable from one computer to another. An option would be to store the data as text. As you said you want to work with a binary file, you are probably storing the variables/structure directly into the file. Some problems you may encounter: - Different type widths. You write a long in one machine where it has 8 bytes, then read it from another where long has 4 bytes. I'd use for the data to be stoed the int*_t types from <stdint.h> to have a fixed width. - Different type alignment. If the alignment of your struct isn't optimal, the compiler will add some padding to fix it. This is not an immediate problem, but if you try to use the same code with a different compiler (which uses slightly different rules) or another version of the same compiler, where those rules have changed, then there will be a nasty mismatch. Solution: use packed structs. - Endianness <http://en.wikipedia.org/wiki/Endianness>. You move it to a computer using a different byte-order. Solution: convert to a file-format endianness before storing in file, convert back when reading. You can use functions like htonl() You can use a framework like XDR <http://en.wikipedia.org/wiki/External_Data_Representation> for that, but I'd start but understanding how to do the things manually. Finally, for your strange request on "how to write down part of an int", you probably want to work with the bytes (use the char type) of the int . Cheers
