Question

On Wi32
I am trying to start a executable who redirects to a filename (current date) e.g. the same as:

Someexecutable.exe > 20101220000000.txt

When I do this from windows cmd.exe everything works fine. However when doing this from my program as shown below the system seems ot either drop the redirect even if it creates the file and/or it seems to buffer a large amount of data before flushing to disk.
I can’t change the executable that is being run.
The program beeing executed now only writes to stdout, but remember I can’t change this at all. (the simplest way woud be to just do stdout = filehandle; but I that is sadly impossible for me right now!)

(Not required: Also the program waits as system() this is not required but what is the simplest way of detaching the program being run via system() )

#include <stdio.h>
#include <stdlib.h>
#include <time.h>

int main(int argc, char *argv[])
{
  char   execstr[512];
  char   s[30];
  size_t i;
  struct tm tim;
  time_t now;

  now = time(NULL);
  tim = *(localtime(&now));
  i   = strftime(s,30,"%Y%m%d%H%M",&tim);

  sprintf(execstr,"someexecutable.exe > %s.txt",s);
  printf("Executing: \"%s\"\n",execstr);

  system(execstr);
  exit(0);
  return 0;
}

Answer 1

I don’t see any reason for this to not work, but if this is the case with you, one of the alternative solution could be to use popen and then read from the pipe for writing in the desired file. Here is some sample code which is printing on the screen. You can write that to file instead of screen/console as per your requirement.

#include <stdio.h>
#include <stdlib.h>
#include <time.h>

int main(int argc, char *argv[])
{
  char   execstr[512];
  char   s[30];
  size_t i;
  struct tm tim;
  time_t now;
  char   buf[128];
  FILE   *pipe;

  now = time(NULL);
  tim = *(localtime(&now));
  i   = strftime(s,30,"%Y%m%d%H%M",&tim);

#if 0
  sprintf(execstr,"a.exe > %s.txt",s);
  printf("Executing: \"%s\"\n",execstr);
#endif /* #if 0 */

   if( (pipe = _popen("a.exe", "rt")) == NULL )
      exit( 1 );

   while(!feof(pipe))
   {
      if (fgets(buf, 128, pipe) != NULL )
         printf(buf);   /* write to the required file here */
   }

   _pclose(pipe);

  return 0;
}