Естественно считать по всем байтам внутри файла, пример из гугла:

C++:





[CODE]
#include
//for std::cout
#include
//for std::string
#include
#include "MD5.h"
using
std
::
cout
;
using
std
::
endl
;
int
main
(
int
argc
,
char
*
argv
[
]
)
{
//Start opening your file
ifstream inBigArrayfile
;
inBigArrayfile
.
open
(
"Data.dat"
,
std
::
ios
::
binary
|
std
::
ios
::
in
)
;
//Find length of file
inBigArrayfile
.
seekg
(
0
,
std
::
ios
::
end
)
;
long
Length
=
inBigArrayfile
.
tellg
(
)
;
inBigArrayfile
.
seekg
(
0
,
std
::
ios
::
beg
)
;
//read in the data from your file
char
*
InFileData
=
new
char
[
Length
]
;
inBigArrayfile
.
read
(
InFileData
,
Length
)
;
//Calculate MD5 hash
std
::
string Temp
=
md5
(
InFileData
,
Length
)
;
cout