file.tellg() stuck on same number after using file.get() and file.seekg()

Question

i think i have a stupid mistake in my code but can't find it.

I try to read a Binary file and scan every 4 bytes for a certain pattern to break a big file apart.

  std::string* filename = new std::string((args > 1?argv[1]:"data.bin"));
  std::cout << filename;
  int filenumber = 0;

  std::ifstream myfile (*filename, std::ios::binary);

  if (myfile.is_open())
  {
    bool newfile = true;
    std::streampos filebegin = 0;
    std::streampos fileend = 0;
    char* buffer = new char[4];

    int oldpos = -1;

    while ( myfile.good() )
    {

        myfile.get(buffer,4);       // get character from file
        int currpos = myfile.tellg();
 //       std::cout << currpos << std::endl;
        if (myfile.good() && buffer[0] == 82 && buffer[1] == 73 && buffer[2] == 70 && buffer[3] == 70){
            if(newfile){
                newfile = false;
                filebegin = myfile.tellg()-std::streampos(3);
                std::cout << "file begin" << std::endl;
            }
            else{
                newfile = true;
                fileend = myfile.tellg()-std::streampos(4);
                char* filebuffer = new char[fileend-filebegin];
                myfile.seekg(filebegin);
                myfile.get(filebuffer,fileend-filebegin);

                std::ostringstream os;
                os << "file" << filenumber << ".bin";

                std::ofstream myofile (os.str());
                filenumber++;
                if (myofile.is_open()){
                    std::cout << "file " << filenumber << std::endl;
                    myofile << filebuffer;
                }
                myofile.close();

                delete[] filebuffer;
            }
        }
        myfile.seekg(myfile.tellg()-std::streampos(2));

        oldpos = currpos;
    }
    myfile.close();
  }

  else std::cout << "Unable to open file";

But after some loops it got stuck on position 3387.

Does some one know what I do wrong?

I use TDM-GCC to compile. edit: It does not even get to the pattern I search.

greetings Wasabi

Answer 1

Perhaps you should replace

myfile.get(filebuffer,fileend-filebegin);

with

myfile.read(filebuffer,fileend-filebegin);

and try again. The reason was already explained by @uesp.