write_to_stdin.cc

#include <stdio.h>
#include <sys/stat.h>
#include <unistd.h>
#include <fcntl.h>

int main(int argc, char* argv[])
{
  char c;
  int fd;
  FILE* file;
  char * myfifo = "/tmp/myfifo";

  mkfifo(myfifo, 0666);
  freopen(myfifo, "r", stdin);

  file = fopen(myfifo, "w");
  fprintf(file, "Hello world\n");
  fflush(file);
  fclose(file);

  do {
    c = getc(stdin);
    printf("%c",c);
  } while( c != EOF);

  unlink(myfifo);
 }