FileToBase64.cpp

#include <iostream>
#include <string>
#include <vector>
#include <fstream> 

using namespace std;

const char* base64_chars{
"ABCDEFGHIJKLMNOPQRSTUVWXYZ"
"abcdefghijklmnopqrstuvwxyz"
"0123456789+/" };

string base64_encode(unsigned const char* input, unsigned const int len) {
    string ret;
    size_t i = 0;
    unsigned char bytes[3];
    unsigned char sextets[4];

    while (i <= (len - 3)) {
        bytes[0] = *(input++);
        bytes[1] = *(input++);
        bytes[2] = *(input++);

        sextets[0] = (bytes[0] & 0xfc) >> 2;    // Cuts last two bits off of first byte
        sextets[1] = ((bytes[0] & 0x03) << 4) + ((bytes[1] & 0xf0) >> 4);   // Takes last two bits from first byte and adds it to first 4 bits of 2nd byte
        sextets[2] = ((bytes[1] & 0x0f) << 2) + ((bytes[2] & 0xc0) >> 6);   // Takes last 4 bits of 2nd byte and adds it to first 2 bits of third byte
        sextets[3] = bytes[2] & 0x3f;   // takes last 6 bits of third byte

        for (size_t j = 0; j < 4; ++j) {
            ret += base64_chars[sextets[j]];
        }

        i += 3; // increases to go to third byte
    }

    if (i != len) {
        size_t k = 0;
        size_t j = len - i; // Find index of last byte
        while (k < j) {     // Sets first bytes
            bytes[k] = *(input++);
            ++k;
        }

        while (j < 3) {     // Set last bytes to 0x00
            bytes[j] = '\0';
            ++j;
        }

        sextets[0] = (bytes[0] & 0xfc) >> 2;    // Cuts last two bits off of first byte
        sextets[1] = ((bytes[0] & 0x03) << 4) + ((bytes[1] & 0xf0) >> 4);   // Takes last two bits from first byte and adds it to first 4 bits of 2nd byte
        sextets[2] = ((bytes[1] & 0x0f) << 2) + ((bytes[2] & 0xc0) >> 6);   // Takes last 4 bits of 2nd byte and adds it to first 2 bits of third byte
        // No last one is needed, because if there were 4, then (i == len) == true

        for (j = 0; j < (len - i) + 1; ++j) {   // Gets sextets that include data
            ret += base64_chars[sextets[j]];    // Appends them to string
        }

        while ((j++) < 4)   // Appends remaining ='s
            ret += '=';

    }

    return ret;

}

string base64_encode_image(const string& path) {
    vector<char> temp;

    ifstream infile;
    infile.open(path, ios::binary);     // Open file in binary mode
    if (infile.is_open()) {
        while (!infile.eof()) {
            char c = (char)infile.get();
            temp.push_back(c);
        }
        infile.close();
    }
    else return "File could not be opened";
    string ret(temp.begin(), temp.end() - 1);
    ret = base64_encode((unsigned const char*)ret.c_str(), ret.size());

    return ret;
}

int main()
{
    string s = base64_encode_image("tst.png");
    std::cout << "Status: " << s << endl;
}