freopen & cout

[Burak Serdar]

Alex Vinokur wrote:
> Hi,
> 
> Where has output-to-cout gone in the program below?
> 
> Thanks,
> 
> ========= C++ code : File foo.cpp : BEGIN =========
> #include <cstdio>
> #include <cassert>
> #include <iostream>
> #include <fstream>
> using namespace std;
> 
> #define FILE_NAME "foobar"
> 
> int main ()
> {
> ofstream ofs;
> 
>   remove (FILE_NAME);
> 
>   ofs.open (FILE_NAME);
>   assert (ofs);
>   assert (ofs.is_open());
> 
> FILE* stdof = freopen (FILE_NAME, "w", stdout);

This call to freopen closes stdout, therefore you cannot print anything 
using cout after this point.



>   assert (stdof);
> 
>   cout << "to cout (first time)" << endl;   // Problematic line
>   ofs  << "to ofs  (first time)" << endl;
>   cout << "to cout (second time)" << endl;  // Problematic line
>   ofs  << "to ofs  (second time)" << endl;
> 
>   ofs.close();
>   assert (!ofs.is_open());
> 
> int rc = fclose (stdof);
>   assert (!rc);
> 
>   return 0;
> }
> ========= C++ code : File foo.cpp : END ===========
> 
> 
> ========= Compilation & Run : BEGIN =========
> 
> $ g++ -v
> [---omitted---]
> gcc version 3.3.1 (cygming special)
> 
> $ g++ -W -Wall foo.cpp
> 
> $ a
> // No output; Where has output-to-cout gone?
> 
> $ cat foobar
> to ofs  (first time)
> to ofs  (second time)
> 
> ========= Compilation & Run : END ===========
> 
> 
> --
>    =====================================
>    Alex Vinokur
>      mailto:alexvn@connect.to
>      http://up.to/alexvn
>    =====================================
> 
> 
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