Question

Byte Array to Structure Conversion in C++

Asked by: srinivasakella

Hi,

I have a Byte array in which , different structures are placed back to back
in contiguously.

Now I need to split this byte array into different structures.
 Right Now I am using "memcpy" for parsing. But I would like to have custom function
for converting this byte array into desired structure.

My idea is split the byte array into different byte arrays according to the size of the structures.
Then converting these byte arrays into corresponding structures using using some custom function .

I need to do this C++.

Thanks,
Srinivas

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Asked On
2009-02-28 at 11:26:52ID24186975
Topics

C / C++ / C# Editors and IDEs

,

C++ Programming Language

Participating Experts
3
Points
500
Comments
10

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Answers

 

by: vhpgomesPosted on 2009-03-01 at 07:53:26ID: 23768456

You don't have to actually split the array:

// suppose you big byte array is in 'bigarray' variable
 
char* start_of_struct_1 = bigarray;
char* start_of_struct_2 = start_of_struct_1 + size_of_struct_1;
char* start_of_struct_3 = start_of_struct_2 + size_of_struct_2;
char* start_of_struct_4 = start_of_struct_3 + size_of_struct_3;
 
// and so on...
                                              
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by: jkrPosted on 2009-03-01 at 07:55:14ID: 23768469

You can do that without 'memcpy()' - just cast a pointer accordingly, e.g.

struct foo1 {
 
  char name[16];
  int age;
  double salary;
};
 
struct foo2 {
 
  int key;
  char name[8];
  int items;
  double price;
};
 
BYTE arr[1024];
 
// fill array...
 
foo1* p1 = (foo1*) arr;
cout << p1->name << " " << p1->salary << endl;
 
foo2* p2 = (foo2*) arr;
cout << p2->name << " " << p2->price << endl;

                                              
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by: jkrPosted on 2009-03-01 at 07:56:11ID: 23768473

BTW, the same can be done using a C++ style cast like

foo1* p1 = reinterpret_cast<foo1*>(arr);

also, but the results are basically the same.

 

by: KimpanPosted on 2009-03-05 at 14:23:20ID: 23811659

Hmm that would work if you knowthe alignment of the structure. Or if the struct was saved with default compiler settings and you use the same compiler version when you try to read it back from byte array to struct.

Btw, this sounds like homework I did long time ago...

Long time no see jkr!

 

by: jkrPosted on 2010-03-03 at 18:59:53ID: 27299371

Um, sorry, but splitting the array won't help very much, so I tend to object to a split here. It is the C/C++ way to tell the compiler to look at a memory region as a struct by casting to a pointer to a struct. Reading and interpreting single fields by offsets is not really efficiant.

20120131-EE-VQP-002

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