Chunk Upload API questions for C++

I am using C++ in my application to upload large files to BOX. I am using the Chunk Upload API to do this.

For the call to Upload Part, this is the cURL request on the website -

curl -X PUT $UPLOAD_PART_URL \
    -H "authorization: Bearer $TOKEN" \
    -H "content-range: bytes $FROM-$TO/20000000" \
    -H "content-type: application/octet-stream" \
    -H "digest: sha=$SHA1_BASE64" \
    -H "Expect:" \
    --data-binary @/tmp/part >> /tmp/${UPLOAD_SESSION_ID}

Since I am using C++, what would my request look like for the data-binary part ?

 Here file_bytes_str has the data bytes for the part to be uploaded. The header has the correct fields appended.

Would my request be this ?
                RestClient::Response resp = this->put(url,filebytes_str);
OR
                std::string body;
                {
                  std::string body = "{\"name\":\"" + filebytes_str + "\"}";

               }
                RestClient::Response resp = this->put(url,body);