Question

I have question about interpreting strings as packed binary data in C++. In python, I can use struct module. Is there a module or a way in C++ to interpret strings as packed binary data without embedding Python?

Answer 1

As already mentioned, it is better to consider this an array of bytes (chars, or unsigned chars), possibly held in a std::vector, rather than a string. A string is null terminated, so what happens if a byte of the binary data had the value zero?

You can either cast a pointer within the array to a pointer to your struct, or copy the data over a struct:

#include <memory>

#pragma pack ( push )
#pragma pack( 1 );

struct myData
{
    int data1;
    int data2;
    // and whatever
};

#pragma pack ( pop ) 


char* dataStream = GetTheStreamSomehow();

    //cast the whole array
myData* ptr = reinterpret_cast<myData*>( dataStream );
    //cast from a known position within the array
myData* ptr2 = reinterpret_cast<myData*>( &(dataStream[index]) );

    //copy the array into a struct
myData data;
memcpy( &data, dataStream, sizeof(myData) );

If you were to have the data stream in a vector, the [] operator would still work. The pragma pack declarations ensure the struct is single byte aligned – researching this is left as an exercise for the reader. 🙂