Parsing a binary file. What is a modern way?

Question

I have a binary file with some layout I know. For example let format be like this:

• 2 bytes (unsigned short) - length of a string
• 5 bytes (5 x chars) - the string - some id name
• 4 bytes (unsigned int) - a stride
• 24 bytes (6 x float - 2 strides of 3 floats each) - float data

The file should look like (I added spaces for readability):

5 hello 3 0.0 0.1 0.2 -0.3 -0.4 -0.5 

Here 5 - is 2 bytes: 0x05 0x00. "hello" - 5 bytes and so on.

Now I want to read this file. Currently I do it so:

• load file to ifstream
• read this stream to char buffer[2]
• cast it to unsigned short: unsigned short len{ *((unsigned short*)buffer) };. Now I have length of a string.
• read a stream to vector<char> and create a std::string from this vector. Now I have string id.
• the same way read next 4 bytes and cast them to unsigned int. Now I have a stride.
• while not end of file read floats the same way - create a char bufferFloat[4] and cast *((float*)bufferFloat) for every float.

This works, but for me it looks ugly. Can I read directly to unsigned short or float or string etc. without char [x] creating? If no, what is the way to cast correctly (I read that style I'm using - is an old style)?

P.S.: while I wrote a question, the more clearer explanation raised in my head - how to cast arbitrary number of bytes from arbitrary position in char [x]?

Update: I forgot to mention explicitly that string and float data length is not known at compile time and is variable.

Answer 1

If it is not for learning purpose, and if you have freedom in choosing the binary format you'd better consider using something like protobuf which will handle the serialization for you and allow to interoperate with other platforms and languages.

If you cannot use a third party API, you may look at QDataStream for inspiration

• Documentation
• Source code