Graphics Programs Reference
In-Depth Information
printf("The 'unsigned int' data type is\t %d bytes\n", sizeof(unsigned int));
printf("The 'short int' data type is\t %d bytes\n", sizeof(short int));
printf("The 'long int' data type is\t %d bytes\n", sizeof(long int));
printf("The 'long long int' data type is %d bytes\n", sizeof(long long int));
printf("The 'float' data type is\t %d bytes\n", sizeof(float));
printf("The 'char' data type is\t\t %d bytes\n", sizeof(char));
}
This piece of code uses the
printf()
function in a slightly different way.
It uses something called a format specifier to display the value returned from
the
sizeof()
function calls. Format specifiers will be explained in depth later,
so for now, let's just focus on the program's output.
reader@hacking:~/booksrc $ gcc datatype_sizes.c
reader@hacking:~/booksrc $ ./a.out
The 'int' data type is 4 bytes
The 'unsigned int' data type is 4 bytes
The 'short int' data type is 2 bytes
The 'long int' data type is 4 bytes
The 'long long int' data type is 8 bytes
The 'float' data type is 4 bytes
The 'char' data type is 1 bytes
r
eader@hacking:~/booksrc $
As previously stated, both signed and unsigned integers are four bytes in
size on the
x
86 architecture. A float is also four bytes, while a char only needs
a single byte. The
long
and
short
keywords can also be used with floating-point
variables to extend and shorten their sizes.
0x263
Pointers
The EIP register is a pointer that “points” to the current instruction during a
program's execution by containing its memory address. The idea of pointers
is used in C, also. Since the physical memory cannot actually be moved, the
information in it must be copied. It can be very computationally expensive to
copy large chunks of memory to be used by different functions or in differ-
ent places. This is also expensive from a memory standpoint, since space for
the new destination copy must be saved or allocated before the source can be
copied. Pointers are a solution to this problem. Instead of copying a large
block of memory, it is much simpler to pass around the address of the begin-
ning of that block of memory.
Pointers in C can be defined and used like any other variable type.
Since memory on the
x
86 architecture uses 32-bit addressing, pointers are
also 32 bits in size (4 bytes). Pointers are defined by prepending an asterisk (
*
)
to the variable name. Instead of defining a variable of that type, a pointer is
defined as something that points to data of that type. The pointer.c program
is an example of a pointer being used with the
char
data type, which is only
1byte in size.
