base64 encoding of unsigned char array image c++

Question

How can I encode a vector of uint8_t rgb values to base64 string?

minimal example to consider:

let's suppose i have an image of size 1x1x3 i.e only one pixel with RBG value = {255,0,0} how to convert this to a base64 string such that the image can be validated here

i have an vector of uint8_t values of an image, say pixels (vector<uint8_t> pixels), i want to encode this to base64 encoding,which is to be used in a gltf exporter based on c++.

the size of image is 512x512x3;

i am using this function (found on stackoverflow itself)to encode to base64 string:

static inline bool is_base64(unsigned char c) {
    return (isalnum(c) || (c == '+') || (c == '/'));
}

std::string base64_encode(unsigned char* bytes_to_encode,
    unsigned int in_len) {
    std::string ret;
    int i = 0;
    int j = 0;
    unsigned char char_array_3[3];
    unsigned char char_array_4[4];

    const char* base64_chars =
        "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
        "abcdefghijklmnopqrstuvwxyz"
        "0123456789+/";

    while (in_len--) {
        char_array_3[i++] = *(bytes_to_encode++);
        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++) ret += 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++) ret += base64_chars[char_array_4[j]];

        while ((i++ < 3)) ret += '=';
    }

    return ret;
}

when i try to validate the generated gltf through khronos-gltf-validator it says image format unrecognised.