read specific address in memory using C

Question

could anybody explain me how to read DWORD ,WORD ,BYTE in C from specific address in memory?
for example, base address that is returned using MapViewOfFile() function,how can I read a consecutive BYTE,WORD, or DWORD using C ?
Thanks.

Please realise that there is no BYTE, WORD or DWORD defined in C. They probably are an artifact typedeffed by the windows programming environment. In C, you can just dereference *any* pointer type p by using `*p`. — wildplasser, Apr 30 '13 at 23:19

score 1 · Answer 1 · answered Apr 30 '13 at 23:02

Assuming that the address is aligned suitably for the datatype you are using - this is important as in some architectures, it's invalid to access an "unaligned" address!

In C:

void *address = MapViewOfFile(...);
DWORD *dword_ptr = (DWORD *)address; 
WORD  *word_ptr = (WORD *)address;
BYTE  *byte_ptr = (BYTE *)address;

In C++, the pattern is similar, but instead of a basic C style cast, you should use reinterpret_cast<type*>(address), where type is DWORD, WORD, BYTE, etc. E.g.:

DWORD *dword_ptr = reinterpret_cast<DWORD *>(address);

score 1 · Accepted Answer · edited Apr 30 '13 at 23:04

MapViewOfFile() returns LPVOID which is a typedef of void*. You'll need a cast.

The easiest thing to do would be to read a byte at a time. You don't specify if there's any kind of performance requirement here (nor do you specify your platform, arch, etc), so I'll assume a "byte at a time" is ok.

Note: WORD is defined as short and should be 16-bits in Win32. DWORD is an int and should be 32-bits in Win32.

LPVOID pvAddr= MapViewOfFile(...);

BYTE* pBytes= (BYTE*)pvAddr;

BYTE firstByte= pBytes[0]; /* copy first byte */

WORD w;
memcpy(&w, pBytes+1, 2); /* copy the next two bytes */

DWORD dw;
memcpy(&dw, pBytes+3, 4); /* copy the next 4 bytes */

Hope that helps.

better to use markdown code blocks than trying to inject `` tags directly. — Evan Teran, Apr 30 '13 at 23:05

Evan Teran · Answer 3 · 2013-05-01T18:10:25.087

Well your question has basically two parts:

could anybody explain me how to read DWORD ,WORD ,BYTE in C from specific address in memory?

That's easy, but probably not what you want, you simply cast the address to a pointer of the desired type.
```
DWORD x = *((DWORD *)address);
```
for example, base address that is returned using MapViewOfFile() function,how can I read a consecutive BYTE,WORD, or DWORD using C ?

That's also not too bad. You are getting a void* from MapViewOfFile, simply cast it or assign it to an appropriate pointer type and then you can use it like an array:
```
DWORD *p = MapViewOfFile(...);
DWORD x = p[1]; // second DWORD of the mapped file
```

I think you mean second DWORD rather than second byte on that last line? — Caleb, Apr 30 '13 at 23:07

score 0 · Answer 4 · edited May 23 '17 at 12:18

0

MapViewOfFile returns an LPVOID (which is equivalent to a void *) so it can be read like any other pointer.

edited May 23 '17 at 12:18

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answered Apr 30 '13 at 23:02

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read specific address in memory using C

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