Re: [Dev-C++] fread get stuck

[Per W. <pw...@ia...>]

Note that
  std::cout << "Hello world" << std::endl;
is also file I/O. It's just that in this case, std::cout happens to be
a predefined stream that maps to the standard-out file stream.

No real difference from using
  printf("Hello world\n");
or
  fprintf(stdout,"Hello world\n");
or
  fwrite("Hello world\n",1,12,stdout);

If you want to generate portable files, then you must yourself split the
integer into bytes and emit them byte for byte. You can do this with
something like:
  buf[0] = a & 0xff;
  buf[1] = (a >> 8) & 0xff;
  buf[2] = (a >> 16) & 0xff;
  buf[3] = (a >> 24) & 0xff;
and then use fwrite to write out buf.

/pwm

On Fri, 20 Jul 2007, Kristian Magnani wrote:

> Yes, the fopen lacked the "b" flag. Now it's working fine, Thanks a lot!
>
> I agree that the code mixes C and C++ I/O, but file I/O is done just with C-like file I/O, isn't it? C++ file I/O would imply in use of stream classes...
>
> Regarding the reading / writing integers, is there a way to specify the byte order, or should my code itself decompose the integers into bytes (using shifting operations and bit masks)?
>
> Thanks again.
>
> ----- Original Message ----
> From: Per Westermark <pw...@ia...>
> To: Kristian Magnani <kri...@ya...>
> Cc: dev...@li...
> Sent: Thursday, July 19, 2007 7:29:20 PM
> Subject: Re: [Dev-C++] fread get stuck
>
> It's a bit hurtfull to my eyes to see source code that mixes C and C++
> file I/O. I would recommend that you use one or the other.
>
> In your case, you have forgotten an important difference between Windows
> and Unix. In Windows, there is a difference between binary and ASCII
> files. When writing to a file opened in ASCII mode, any character "\n"
> will be converted to "\r\n" (CR+LF), and when reading to a file opened in
> ASCII mode, the caracters "\r\n" will be converted to a "\n".
>
> In your case, you are using fread() and fwrite() to read and write as if
> the integers are binary data. That requires you to add a "b" to the mode
> string of fopen().
>
> Note that you are using a non-portable way if reading and writing
> integers. The data is read and written in the byte order of the machine
> you are currently using. A better way to create binary data files is to
> beforehand specify a byte order, and then write the integers as separate
> bytes.
>
> /pwm
>
> On Thu, 19 Jul 2007, Kristian Magnani wrote:
>
> > Hi, all!
> >
> > I've been using gcc in linux for a while, but now I'm trying do compile some example codes I've under Dev-C++, and I'm facing some problems.
> >
> > Below follow two programs: one opens a file where it write 1000 random numbers and the other open a file to read numbers and print them into the screen. Thet work perfectly under gcc/linux, but at Dev-C++/windows the program that reads the file get stuck at a particular number. For the same file, it always stops reading at the same line, although for different files, it stops at different lines.
> >
> > I suspect it's something defined as open behaviour in C/C++ specification, because the same programs work fine at gcc/linux, but I don't know what. Does anyone have an idea what I'm doing wrong?
> >
> > Thanks!
> >
> >
> >
> > #include <iostream>
> > #include <stdlib.h>
> >
> > using namespace std;
> >
> > int main (int argc, char *argv[])
> > {
> >   /* inicializa gerador de numeros aleatorios */
> >   srand(time(NULL));
> >
> >   /* abre arquivo para escrita, criando se nao existir */
> >   /* cursos posicionado no inicio do arquivo */
> >   FILE* file = fopen(argv[1], "w+");
> >   if (file == NULL)
> >   {
> >     cout << "Erro ao criar arquivo." << endl;
> >   }
> >   else
> >   {
> >     for (int i = 0; i < 1000; i++)
> >     {
> >
> >       /* pausa execucao */
> >       if (i % 100 == 0 && i > 0) cin.get();
> >
> >       /* escreve um numero aleatorio no arquivo aberto */
> >       int aleatorio = rand() % 1000;
> >       cout << i + 1 << "\tEscrevendo '" << aleatorio
> >            << "' no arquivo '" << argv[1] << "'." << endl;
> >       int elementosEscritos = fwrite(&aleatorio, 1, sizeof(int), file);
> >       if (elementosEscritos < 0)
> >       {
> >         cout << "Erro ao escrever em arquivo.";
> >       }
> >     }
> >   }
> >
> >   /* fecha arquivo */
> >   fclose(file);
> >
> >   /* pausa execucao */
> >   cin.get();
> >
> >   return 0;
> > }
> >
> >
> >
> >
> >
> >
> > #include <iostream.h>
> > #include <stdlib.h>
> >
> > using namespace std;
> >
> > int main (int argc, char *argv[])
> > {
> >
> >   /* abre arquivo para leitura */
> >   /* cursos posicionado no inicio do arquivo */
> >   FILE* file = fopen(argv[1], "r+");
> >   if (file == NULL)
> >   {
> >     cout << "Erro ao abrir arquivo '" << argv[1] << "'." << endl;
> >   }
> >   else
> >   {
> >     int i = 0;
> >     int elementosLidos;
> >     int aleatorio;
> >
> >     /* le um numero do arquivo aberto */
> >     while (elementosLidos = fread(&aleatorio, sizeof(int), 1, file) > 0)
> >     {
> >       i++;
> >       cout << i << "\tLeu '" << aleatorio
> >            << "' (" << elementosLidos << " elementos) do arquivo '"
> >            << argv[1] << "'." << endl;
> >     }
> >   }
> >
> >   /* fecha arquivo */
> >   fclose(file);
> >
> >   /* pausa execucao */
> >   cin.get();
> >
> >   return 0;
> > }
> >
> >
> >
> >
> >
> >
> > ____________________________________________________________________________________
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