How to Create an Input Stream from Read-Only Memory in C ?

Creating an Input Stream from Read-Only Memory

You have a data buffer pointed to by a const char* pointer containing an ASCII string. You want to read the data as if it were a stream, without copying or altering it.

Solution

To achieve this, you can create a custom stream buffer. Here's how:

#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 membuf class contains the stream buffer that reads from the const char* pointer. The imemstream class inherits from membuf and adds the necessary functionality to make it an input stream.

To use imemstream, you can instantiate it and use it like this:

imemstream in(data, size);
in >> value;

This will read the data from the buffer as if it were a stream, without modifying it.

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