如何在c++中将IStream转换为Base64字符串

#include <iostream>
#include <sstream>
#include <fstream>
#include <vector>
#include <algorithm>

std::string base64_encode(const std::vector<unsigned char>& data) {
    const std::string base64_chars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
    std::string encoded_data;
    int i = 0;
    int j = 0;
    unsigned char char_array_3[3];
    unsigned char char_array_4[4];

    for (const auto& byte : data) {
        char_array_3[i++] = byte;
        if (i == 3) {
            char_array_4[0] = (char_array_3[0] & 0xfc) >> 2;
            char_array_4[1] = ((char_array_3[0] & 0x03) << 4) + ((char_array_3[1] & 0xf0) >> 4);
            char_array_4[2] = ((char_array_3[1] & 0x0f) << 2) + ((char_array_3[2] & 0xc0) >> 6);
            char_array_4[3] = char_array_3[2] & 0x3f;

            for (i = 0; i < 4; i++) {
                encoded_data += base64_chars[char_array_4[i]];
            }
            i = 0;
        }
    }

    if (i) {
        for (j = i; j < 3; j++) {
            char_array_3[j] = '\0';
        }

        char_array_4[0] = (char_array_3[0] & 0xfc) >> 2;
        char_array_4[1] = ((char_array_3[0] & 0x03) << 4) + ((char_array_3[1] & 0xf0) >> 4);
        char_array_4[2] = ((char_array_3[1] & 0x0f) << 2) + ((char_array_3[2] & 0xc0) >> 6);

        for (j = 0; j < i + 1; j++) {
            encoded_data += base64_chars[char_array_4[j]];
        }

        while (i++ < 3) {
            encoded_data += '=';
        }
    }

    return encoded_data;
}

std::string istream_to_base64(std::istream& input_stream) {
    std::vector<unsigned char> buffer(std::istreambuf_iterator<char>(input_stream), {});
    return base64_encode(buffer);
}

int main() {
    std::ifstream file("input.txt", std::ios::binary);
    std::stringstream buffer;
    buffer << file.rdbuf();
    std::string base64_string = istream_to_base64(buffer);
    std::cout << "Base64 String: " << base64_string << std::endl;
    return 0;
}