dup2() on stdout [or using disp() on another file stream]

[John W. Eaton]

On 16-Oct-1999, Joao Cardoso <address@hidden> wrote:

| How can I use 'disp' on a file stream other than 'stdout'?
| 
| 'disp' is an easy and nice way to print matrices, without the need to
| create a format string to use on 'fprintf'. I would like to:
| 
|      f_name = tmpnam
|      fout = fopen(f_name,"w");
|      disp(fout, rand(3))        <--- not supporred
|      fclose(fout)
| 
| When I tried to use:
| 
|     f_name = tmpnam
|     fout = fopen(f_name,"w");
|     old = fopen("old","w");
| 
|     dup2(stdout, old); # save old stdout on 'old'?
|     dup2(fout, stdout); # use new stdout
| 
|     disp(rand(3))
| 
|     dup2(old, stdout);  #revert to saved stdout?
| 
| I wasn't able to revert stdout to the original stdout. what is wrong? I
| can't 'fclose(stdout)', either.

What version of Octave are you using?

FWIW, it works for me with 2.0.14 and also with the current
bleeding-edge sources on a Linux system.

Unfortunately, after you put stdout on fout, you also get the prompt
and the commands in the output file.  (You might as well use diary!)

Perhaps it would be better to just implement an fdisp() function that
does what you want?  Or, in the current bleeding-edge sources, Octave
has a `file' data type and a C++-like output operator, so you can
write:

  file = fopen (fname, "w");
  file << rand (3);

to print a formatted matrix to a file.

(I'm not sure that the `<<' operator is a good idea though -- this feature is
still experimental.)

jwe



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