Question

this should be pretty common yet I find it fascinating that I couldn’t find any straight forward solution.

Basically I read in a file over the network into a stringstream. This is the declaration:

std::stringstream membuf(std::ios::in | std::ios::out | std::ios::binary);

Now I have some C library that wants direct access to the read chunk of the memory. How do I get that? Read only access is OK. After the C function is done, I dispose of the memorystream, no need for it.

str() copies the buffer, which seems unnecessary and doubles the memory.

Am I missing something obvious? Maybe a different stl class would work better.

Edit:
Apparently, stringstream is not guaranteed to be stored continuously. What is?

if I use vector<char> how do I get byte buffer?

Answer 1

You can call str() to get back a std::string. From there you can call c_str() on the std::string to get a char*. Note that c_str() isn’t officially supported for this use, but everyone uses it this way 🙂

Edit

This is probably a better solution: std::istream::read. From the example on that page:

  buffer = new char [length];

  // read data as a block:
  is.read (buffer,length);