original.c

#include <stdio.h>
#include <unistd.h>
#include <strings.h>
#include <sys/types.h>

void exit(int);

int main() {
  int pipeFD[2];
  unsigned int reader, writer, i;
  FILE *outputFile = fopen("tmpoutput", "w");

  pipe(pipeFD);
  reader = pipeFD[0]; writer = pipeFD[1];

  for(i = 1; ; i++) {
    if(i > 5) {
      unsigned int outputFD = fileno(outputFile);

      if(fork()) {
        /* I am the parent. */
        char readBuf[20] = {0};

        close(writer);
        sprintf(readBuf, "%d", reader);

        execl("./newbinary", "--hotswapping", readBuf, (char*)0);
        exit(0);
      } else {
        /* I am the child.*/
        FILE *outputStream = fdopen(writer, "w");
        close(reader);

        fprintf(outputStream, "%d\n", i);
        fprintf(outputStream, "%u\n", (unsigned int) outputFD);
        fclose(outputStream);
        exit(0);
      }
    }

    fprintf(outputFile, "Original:\t%d My PID=%d\n", i, getpid());
    fflush(outputFile);

    printf("Original:\t%d My PID=%d\n", i, getpid());
    fflush(stdout);

    sleep(1);
  }
  return 0;
}