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

[Kristian M. <kri...@ya...>]

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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