Linux programming help

[crazeinc]

I'm trying my hand with a little unix programming, but my second execvp in main() below doesn't appear to be working correctly.
A sample call to this would be ./rungenerator 20 1 and the output is as follows:
parent: 27461
child: 27462
0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38
child: 27463

the output should be:
parent: 27461
child: 27462
0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38
child: 27463
1 3 5...etc

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

int main(int argc, char* argv[]){
  int fd[2];
  pid_t child[2];
  char *args[4];

  if(argc != 3){
    write(2,"Invalid # of arguments\n",23);
    return 1;
  }

  args[0]="./generate1";
  args[2]=argv[1];
  args[3]=argv[2];
  args[4]="0";

  printf("parent: %ld\n",(long) getpid());

  if(child[0] = fork())
    child[1] = fork();

  if(!child[0]){
    printf("child: %ld\n",(long) getpid());
    args[1]="even";
    execvp(args[0],args);
  }
  if(!child[1]){
    printf("child: %ld\n",(long) getpid());
    args[1]="odd";
    execvp(args[0],args);
  }

  return 0;
}

here's the code to generate1:

int main(int argc, char* argv[]){
  int which, i, num, fd;
  char buf[3];

  if(argc != 4){
    write(2,"Invalid # of arguments\n",23);
    return 1;
  }

  if(!strcmp(argv[1],"odd"))
    which=1;
  else if(!strcmp(argv[1],"even"))
    which=2;
  else{
    write(1,"Must be odd or even!\n",21);
    return 2;
  }

  srand(which);

  fd = atoi(argv[3]);

  /* if we're counting 0 as even */
  if(which==2)
    write(fd,"0 ",2);

  num = atoi(argv[2]) * 2;
  for(i=which;i<num;i=i+2){
    sprintf(buf,"%d ",i);
    write(fd,buf,3);
  }
  write(fd,"\n",1);

  return 0;
}

Any help would be appreciated. Thanks, PJ.

[Salem]

#ifdef SLAVE
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <unistd.h>
int main(int argc, char* argv[]){
  int which, i, num, fd;
  char buf[3]; /* !! This is way too small given your following usage */
  /*!! it's only large enough for "N \0" (a single digit followed by a space) */

  if(argc != 4){
    write(2,"Invalid # of arguments\n",23);
    return 1;
  }

  if(!strcmp(argv[1],"odd"))
    which=1;
  else if(!strcmp(argv[1],"even"))
    which=2;
  else{
    write(1,"Must be odd or even!\n",21);
    return 2;
  }

  srand(which); /*!! pointless, you're not calling rand() */

  fd = atoi(argv[3]);

  /* if we're counting 0 as even */
  /*!! so why not start with which=0 then if you want to count 0 ? */
  if(which==2)
    write(fd,"0 ",2);

  num = atoi(argv[2]) * 2;
  for(i=which;i<num;i=i+2){
    sprintf(buf,"%d ",i);
    write(fd,buf,3);
  }
  write(fd,"\n",1);

  return 0;
}
#else
#include <stdio.h>
#include <sys/types.h>
#include <unistd.h>
#include <fcntl.h>

int main(int argc, char* argv[]){
  int fd[2];
  pid_t child[2];
  char *args[5];  /*!! not 4, you have an argv[4] below */

  if(argc != 3){
    write(2,"Invalid # of arguments\n",23);
    return 1;
  }

  args[0]="./generate1";
  args[2]=argv[1];
  args[3]=argv[2];
  args[4]=NULL; /*!! NOT "0"; */

  printf("parent: %ld\n",(long) getpid());

  if ( (child[0] = fork()) == 0 ) {
    printf("child: %ld\n",(long) getpid());
    args[1]="even";
    execvp(args[0],args);
  }
  if ( (child[1] = fork()) == 0 ) {
    printf("child: %ld\n",(long) getpid());
    args[1]="odd";
    execvp(args[0],args);
  }

  return 0;
}
#endif



$ gcc -DSLAVE -o generate1 hello.c
$ gcc hello.c
$ ./a.out 10 1 && sleep 2
parent: 26283
child: 26284
0 2 4 6 8 10 12 14 16 18
child: 26285
1 3 5 7 9 11 13 15 17 19

[crazeinc]

thanks for the help.