Question

I’m trying to parse a string manually by spaces without using strtok() or anything from string.h. Does this look like the right approach? When I try this, I keep skipping right past the end of the string.

  char cmd[1024];
  int ret = read(STDIN, cmd, 1023);
  cmd[ret-1] = '\0';

     char * args[128];
     int length = 0;
     char * startptr = cmd;
     char * endptr = cmd;

     while(1){
        if(*startptr == '\n' || *startptr == '\0'){
           break;
        }
        if(*startptr == ' '){
           startptr ++;
           endptr ++;
           continue;
        }
        // startptr is placed
        if(*endptr != '\0' || *endptr != '\n' || *endptr != ' '){
           endptr ++;
           continue;
        }
        // both pointers placed
        char * i = startptr;
        for(i = startptr; i != endptr; i++){
           args[length][i-startptr] = *i;
        }
        length ++;
        startptr = endptr;
        if(*endptr == '\0' || *endptr == '\n'){
           break;
        }

     }

Answer 1

No is not right.Logical expressions must be ‘and’ not ‘or’.
checking for limitations would be good, some times will may interesting effect like ‘change ARG_MAX_LEN to 2’ you get the first character of every word.
Probably this code will work.

 char cmd[1024];
 int ret = readf(cmd, 1, 1023, stdin);

 char args[128][ARG_MAX_LEN]; //two dimensional array 
 int length = 0;
 char * startptr = cmd;
 char * endptr = cmd;
 char *ap, *aep;
 if(ret > 0)
   cmd[ret-1] = '\0';
 else
   cmd[0] = '\0';
 while(*startptr != '\n' && *startptr != '\0')
 {
    if(*startptr == ' '){
       endptr = ++startptr ;
       continue;
    }
    // startptr is placed
    if(*endptr != '\0' && *endptr != '\n' && *endptr != ' '){
       endptr ++;
       continue;
    }
    // both pointers placed
    ap = &args[length][0];
    aep = ap + ARG_MAX_LEN - 1;
    while(startptr != endptr && ap != &args[length+1])
      *ap++ = *startptr++;
    if(length >= 128)
       break;
    length ++;
    startptr = endptr;
 }

If you are want to get command line arguments you should look for character escaping as well.