C# – Serialize a C# class to binary be used by C++. How to handle alignment

alignmentbinaryc

I am currently serializing a C# class into a binary stream using BinaryWriter.

I take each element of the class and write it out using BinaryWriter. This worked fine as the C++ application reading this binary file supported packed structs and hence the binary file could be loaded directly.

Now I have got a request to handle alignment as a new application has popped up which cannot support packed structs. What's the best way to convert the C# class and exporting it out as a binary keeping both 2 byte as well as 4 byte alignment in mind?

The user can choose the alignment.

Best Answer

In serializations of objects in any language alignment should not be an issue, as you know ahead of time how much data is being written and read.

For example, take the following struct:

struct data
{
   char c;
   unsigned int i;
   double d;
}

Depending on how the compiler does memory layout, the size of this struct in memory can be anywhere from 13 to 20 (packed - 32-bit alignment), but that's the memory layout. As far as disk layout is concerned, you are (assuming binary) always going to be writing:

write 1 byte for c
write 4 bytes for i
write 8 bytes for d

Hence when the other side reads it in, be it either Python or C# or whatever else should do the following:

read 1 byte and convert to internal char representation
read 4 bytes and convert to an internal unsigned int representation (remember if in java there is no unsigned int)
read 8 bytes and convert to an internal real or floating point representation

This is pretty much the canonical solution. You should never rely on mass block writes of structures in any language if portability between languages and architectures is an issue.

Also the above does not take into account endianess, which is something you need to consider when serializing integers - usually as easy as converting to network byte order and then back, for writing and reading respectively.

Related Solutions

Python – How to express binary literals in Python

For reference—future Python possibilities:
Starting with Python 2.6 you can express binary literals using the prefix 0b or 0B:

>>> 0b101111
47

You can also use the new bin function to get the binary representation of a number:

>>> bin(173)
'0b10101101'

Development version of the documentation: What's New in Python 2.6

C++ – How to call a parent class function from derived class function

I'll take the risk of stating the obvious: You call the function, if it's defined in the base class it's automatically available in the derived class (unless it's private).

If there is a function with the same signature in the derived class you can disambiguate it by adding the base class's name followed by two colons base_class::foo(...). You should note that unlike Java and C#, C++ does not have a keyword for "the base class" (super or base) since C++ supports multiple inheritance which may lead to ambiguity.

class left {
public:
    void foo();
};

class right {
public:
    void foo();
};

class bottom : public left, public right {
public:
    void foo()
    {
        //base::foo();// ambiguous
        left::foo();
        right::foo();

        // and when foo() is not called for 'this':
        bottom b;
        b.left::foo();  // calls b.foo() from 'left'
        b.right::foo();  // call b.foo() from 'right'
    }
};

Incidentally, you can't derive directly from the same class twice since there will be no way to refer to one of the base classes over the other.

class bottom : public left, public left { // Illegal
};

Best Answer

Related Solutions

Python – How to express binary literals in Python

C++ – How to call a parent class function from derived class function

Related Topic