c - In multi thread application how can I redirect stderr & stdout in separate file as per thread?

Question

I have multi thread application in which I'm creating a thread like this:

int main(int argc,char *argv[])
{
    pthread_t thread_id[argc-1];
    int i;
    struct parameter thread_data[argc-1];
    int status;
    for(i=0;i<argc-1;i++)
    {
      thread_data[i].ip_filename = argv[i+1];
      strcpy (thread_data[i].op_filename,argv[i+1]);
      strcat (thread_data[i].op_filename,".h264");
    }

    for(i=0;i<argc-1;i++)
    {
      pthread_create (&thread_id[i], NULL , &thread_function, &thread_data[i]);
    }      
}

Now in the thread function, I want to redirect stderr & stdout in one separate file as per thread. Something like a thread log file.

How can I do so?

Edit:

If thread specific prints can be displayed on different terminal..? I mean if there are 2 threads then it opens 2 terminals & prints each threads data on different terminals.

Answer 1

If you really must do this...

First you need to create 2 pthread_key_ts, one for stdout and one for stderr. These can be created using pthread_key_create, and they must be accessable from all threads. Let's call them stdout_key and stderr_key.

When a thread is being created:

FILE *err = ..., *out = ...;
pthread_setspecific(stdout_key, out);
pthread_setspecific(stderr_key, err);

and then in your header file:

#define stdout (FILE*)pthread_getspecific(stdout_key)
#define stderr (FILE*)pthread_getspecific(stderr_key)
#define printf(...) fprintf(stdout, ##__VA_ARGS__)

then just use:

fprintf(stderr, "hello
");
fprintf(stdout, "hello
");
printf("hello
");

I don't recommend this approach though.