process - Operating system processes in .c -

can explain me argc , argv in code , why variables parameters in main function? had in lectures example showed both variables i'm using them without knowing do.

main (argc, argv)     char *argv[];     {         int fd;         extern int errno;         if(argc < 2){             fprintf(stderr, "no file\n");             exit(1);         }          if((fd = creat(argv[1], 0777)) < 0){             fprintf(stderr, "cannot creat file %s\n", argv[1]);             exit(1);         }              switch (fork()) {         case -1:             fprintf(stderr, "fork error\n");             exit(1);         case 0:             close(1);             dup(fd);             close(fd);             execl("/bin/pwd", "pwd", null);             perror("exec");             break;         default:             close(fd);      }       exit(0);     } 

argc int giving program number of arguments passed program operating system. argv array of null-terminated strings containing actual arguments passed program.

the exact parameters operating system dependent, argv[0] executable name including path, while argv[argc] null pointer. (thanks @weathervane pointing out) versions of c standard require argv[argc] null pointer, , prior precedent hosted systems required ('freestanding' — aka embedded — systems run under different rules, now).

not programs require command-line arguments, integral part of operating system.

the c standard requires following definition if both parameters used:

int main(int argc, char *argv[]) ... 

i doubt k&r c used in production code anymore.