Pfthb

I understand if you have an array, and you do sizeof, it gives you the number of bytes that block of memory occupies, but I have some confusion regarding the follow situation.

int mylen(const char *str) 
 return sizeof(str);


int main(void) 
 char str = "hello";

 printf("%dn", sizeof(str)); // this gives 6
 printf("%dn", mylen(str)); // this gives 8

I understand mylen is just returning the sizeof char pointer, therefore 8, but in that case, why the first one works? It this the subtle distinction between str and char *?

It is the same reason why in

char foo[6];
sizeof(foo); // yields 6

and in

char *bar;
sizeof(bar); // yields 8 (or in general: the size of a pointer on your system)

btw, since the result of the sizeof-operator is of type size_t, your mylen() should return size_t (defined in <stddef.h>) instead of int.

Also, if you want to printf() a size_t you'll have to use "%zu", not "%d".

For more detail you might want to read something on array-to-pointer decay: Why do arrays in C decay to pointers?