Thread: I don't understand K&R example

It's the same thing as the strcpy() function:

Code:

#include <string.h>

int main(void)
{
  char str[50];

  strcpy(str, "Hello, world!");
  return 0;
}

See? str's contents are not defined when you pass str to strcpy(). That's because strcpy() fills the array! If the function is meant to accept a string and then manipulate the data in some way then you'd need to fill str with something meaningful before you used it. For example:

Code:

#include <stdio.h>

int main(void)
{
  char str[50];

  puts(str);
  return 0;
}

puts() isn't designed to accept an undefined string so you'll just get garbage output. So there's no universal "You don't have to fill the character array before passing it to a function" rule. It depends on what the function expects.