cout stream manipulations

[graeth]

Basically, I'm trying to write a progress indicator, first I write two characters as limits, and then go back and fill the space with characters as the situation warrants, vis.

void progress(long n,long x)
{
   float p=x*0.05, oo=p;

   cout<<"[                    ]";
   long pos=cout.tellp();
   cout.seekp(pos-21);

   for(n,x ; n<=x ; ++n)
      {
         if( n>oo-1 && n<oo+1 )
            {
               cout<<"."<<flush;
               oo=oo+p;
            }
      }
}

If I was to instead write that to a file, it would work perfectly.

It seems that while cout will happily tellp(), it will not obey the directives of a seekp().

Is the cout stream limited in some way that would prevent normal stream manipulations?

[Gabriel Fleseriu]

std::cout is an output stream. You cannot read from cout, nor can you "rewind" the file pointer.

[graeth]

Yet I can successfully perform the same operation with an ofstream object's output stream.

I don't understand why only some stream manipulations work, for instance, i can read the position of cout's put pointer, but not position it myself.

It seems logical that I should be able to manipulate any output stream until it's flushed from the buffer.

[Gabriel Fleseriu]

Well, once the output is on the screen, the stream would be flushed, I'd say.

I can't give you a solution -- never tried what you want to do. File and screen buffers probably have different sizes. I expect the screen buffer to get flushed much oftener than a file buffer.

Have a look at the timer lib from boost, it has a progress indicator

[graeth]

I had thought it wasn't flushing until I told it to, but it might be.

Do you know of a command to withhold stream synchronisation until stated otherwise?