Given that everything lives in memory and that you now know how to find the address where data starts, the next question is “How many bytes does this data type consume?”
Using sizeof() you can find the size of a data type. For example,
int main(int argc, const char * argv[])
{
int i = 17;
int *addressOfI = &i;
printf("i stores its value at %pn", addressOfI);
*addressOfI = 89;
printf("Now i is %dn", i);
printf("An int is %zu bytesn", sizeof(int));
printf("A pointer is %zu bytesn", sizeof(int *));
return 0;
}
We see yet another new token in the calls to printf(): %zu. The sizeof() function returns a value of type size_t, for which %zu is the correct placeholder token. This one’s not very common in the wild.
Build and run the program. If your pointer is 4 bytes long, your program is running in 32-bit mode. If your pointer is 8 bytes long, your program is running in 64-bit mode.
sizeof() will also take a variable as an argument, so you could have written the previous program like this:
int main(int argc, const char * argv[])
{
int i = 17;
int *addressOfI = &i;
printf("i stores its value at %pn", addressOfI);
*addressOfI = 89;
printf("Now i is %dn", i);
printf("An int is %zu bytesn", sizeof(i));
printf("A pointer is %zu bytesn", sizeof(addressOfI));
return 0;
}