The way to do this is to create a suitable stream buffer. This can, e.g., be done like this:
#include <streambuf>
#include <istream>
struct membuf: std::streambuf {
membuf(char const* base, size_t size) {
char* p(const_cast<char*>(base));
this->setg(p, p, p + size);
}
};
struct imemstream: virtual membuf, std::istream {
imemstream(char const* base, size_t size)
: membuf(base, size)
, std::istream(static_cast<std::streambuf*>(this)) {
}
};
The only somewhat awkward thing is the const_cast<char*>()
in the stream buffer: the stream buffer won’t change the data but the interface still requires char*
to be used, mainly to make it easier to change the buffer in “normal” stream buffers. With this, you can use imemstream
as a normal input stream:
imemstream in(data, size);
in >> value;