[C++-sig] interfacing headle binary file library, raw pointer and buffer

[Nat Goodspeed]

heroxbd at gmail.com wrote:

> I am trying to interface a binary file library using py++.
> 
> There is a function in the library like
> 
>       int read(void* buffer, size_t len)
> 
> which is hard to wrap. It read a piece (size len) of the file, and store
> it in buffer, and then return the buffer length (most likely equal to len).

You want to write a C++ wrapper function something like this:

std::string wrapped_read(size_t len)
{
     // manually allocate buffer of size 'len',
     // e.g. by using std::vector<char>
     int bytes_read = read(buffer, len);
     return std::string(buffer, bytes_read);
     // If you literally used 'new' or 'malloc' to obtain your 'buffer',
     // rather than a type such as std::vector which will release
     // its dynamic memory automatically, of course the 'return'
     // above would leak 'buffer'. In that case you'd have to declare
     // std::string result(buffer, bytes_read);
     // ...manually release 'buffer'...
     // return result;
}

Then wrap the C++ function wrapped_read() as the Python function "read".

Boost.Python is very happy passing std::string in either direction. 
Trying to directly use char* or void* buffers is perilous and will, as 
you remark, make the consumers of your library unhappy.