Can a Custom Stream Buffer Be Used to Read Data from Constant Memory as if It Were Streaming from a File?

Input Stream from Constant Memory

Problem

Given a constant char* pointer to an ASCII string, can you devise a solution to read the data as if it were streaming from a file? The crucial requirement is that the data should remain unmodified.

Solution: Custom Stream Buffer

The solution lies in creating a custom stream buffer. Here's a custom implementation:

#include <streambuf>
#include <istream>

struct membuf: std::streambuf {
    membuf(char const* base, size_t size) {
        char* p(const_cast<char*>(base));  // Casting for interface compatibility
        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)) {}
};

Usage

With this custom buffer, you can create an input stream wrapped around your constant data:

// data points to a string "42 3.14 blah"
imemstream in(data, data_size);
int x;
float y;
std::string w;
in >> x >> y >> w;

This approach allows you to read from the constant memory without altering the original data, unlike string streams that require copying.

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