Why is sizeof(msg) shorter than the string?

Question

I have just started to learn how to program and I am using this book called Head First C. There are sections in the book called Brain Power. In one of these sections it was written.

void fortune_cookie(char msg[])
{
  printf("Message reads: %s\n", msg);
  printf("msg occupies %i bytes\n", sizeof(msg));
}

The output:

Cookies make you fat

msg occupies 8 bytes

The Brain Power question was: Why do you think sizeof(msg) is shorter than the length of the whole string? What is msg? Why would it return different sizes on different machines?

Answer 1

In this particular case

 char msg[]

is same as

 char * msg

so what you're really seeing is the output of sizeof(char *).

As the size of a pointer is dependent on the architecture/compiler, you'll see different output in different machine.

Also, please note, as the sizeof operator produces a result of type size_t, you should be using %zu format specifier to print the result.