How to Convert C FILE* to C++ iostream

When we deal with a lot of C libraries in our C++ code, there may be cases where we need to convert the C FILE* into C++ iostream. Boost iostreams can help to deal with such problems easily. Here's an example how to do it.

#include <iostream>
#include <cstdio>
#include <unistd.h>
#include <boost/iostreams/device/file_descriptor.hpp>
#include <boost/iostreams/stream.hpp>

void write() {
    FILE* fp = fopen("whatever.txt", "w");
    if (fp == NULL) {
        perror("fopen error");
    }
    int fd = fileno(fp);
    boost::iostreams::stream_buffer<boost::iostreams::file_descriptor_sink> bis(fd);
    std::ostream os(&bis);
    os << "Hello World!" << std::endl;

    fclose(fp);
}

void read() {
    FILE* fp = fopen("whatever.txt", "r");
    if (fp == NULL) {
        perror("fopen error");
    }
    int fd = fileno(fp);
    boost::iostreams::stream_buffer<boost::iostreams::file_descriptor_source> bis(fd);
    std::istream is(&bis);
    while (is) {
        std::string line;
        std::getline(is, line);
        std::cout << line << std::endl;
    }
    fclose(fp);
}

int main() {
    write();
    read();

    return 0;
}