C++ Cast binary array to a class

Question

How can I cast a binary array to a known class?

Essentially I have a byte array of data like so:

unsigned char * buff[sizeof(MyClass)];

I'm using unsigned char for each byte as I assume it is a length of 1 byte.

How can I cast this array to what I know the data represents? I have taken the data from memory of MyClass, and put it in this buffer - now I need to cast it back to MyClass.

I've seen reinterpret_cast but I'm not sure if it would apply here.

What you have is an array of character pointers. I doubt that's what you intended. And yes, you can use reinterpret_cast, but why do you want to do this in the first place? — Taylor Brandstetter
– Taylor Brandstetter, Commented Jan 3, 2014 at 23:13
@TaylorBrandstetter By an array of character pointers, I actually meant to have a pointer to an array of characters. How can I fix this? — Christian Stewart
– Christian Stewart, Commented Jan 3, 2014 at 23:15
unsigned char * buff; buff = new unsigned char[sizeof(MyClass)]; — BWG
– BWG, Commented Jan 3, 2014 at 23:16
You don't need a pointer to an array, you just need an array. If you declare unsigned char buff[sizeof(MyClass)]; and do reinterpret_cast<MyClass *>(buff), buff will end up acting like an unsigned char *. — Taylor Brandstetter
– Taylor Brandstetter, Commented Jan 3, 2014 at 23:17

ScarletAmaranth · Accepted Answer · 2014-01-03 23:15:37Z

3

unsigned char* buff[sizeof(MyClass)] is an array of unsigned char*, which is likely to be 4 or 8 times bigger than what you're expecting. (32 and 64bit platforms respectively, although, there are architectures that have even different pointer sizes - nitpick protection)

To answer the casting part of the question, reinterpret_cast<T*>(buff) will handle the chunk as T*.

answered Jan 3, 2014 at 23:15

ScarletAmaranth

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7 Comments

Christian Stewart Over a year ago

Thanks, I've changed unsigned char* to just unsigned char.

ScarletAmaranth Over a year ago

@ChristianStewart Also if you specified what you're using it for, I would likely tell you you're doing it wrong and suggest a better way of doing it, whatever it is :). (In general, it is rarely the case you need to handle memory as a chunk of bytes rather than a type-rich "environment".)

Christian Stewart Over a year ago

Well, I've loaded a known data structure (of classes) from another process using ReadProcessMemory into that buffer (unsigned chars as they are size 1 byte right?) and am now re-casting it to the known data structure (a single class). A couple issues I see with this are there are POINTERS in the data, which point to absolutely nothing within MY process, so I have to resolve those when called..

ScarletAmaranth Over a year ago

@ChristianStewart ah, right, then such buffers aren't a terrible idea, and yeah, unsigned char will be 1 byte, however-many bits that may be in arcane corners of the universe

Christian Stewart Over a year ago

Yeah, now the problem is, all of the pointers point to things in ANOTHER PROCESS, so I have to go through all of them and load them int o the local process.. oh lord..

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