Correct usage of socketcan_interface - hex2dec

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I've recently started using the socketCAN_interface component of ros_canopen to get data from a Kuebler encoder. My code is relatively straight forward, I receive messages on a particular CAN-ID using the following:

    can::CommInterface::FrameListener::Ptr one_frame = driver.createMsgListener(can::MsgHeader(0x101), handleFrame101);

Which calls the following method, writing data to a float which is a global variable:

void handleFrame101(const can::Frame &f){
        // handle specific frame
        std::string frame = can::tostring(f, true); //Break frame into string to extract data
        std::string data = frame.substr(frame.find("#")+1);
        //Check if data matches expected data length from frame, length/2 as dlc is hex (2 bytes per char)
        if( (data.length()/2) == int(f.dlc) ){
            uint64_t output;
            std::stringstream ss;
            ss << std::hex << data;
            ss >> output;
            extension = output;
        }else{
            extension = 0;
        }
    }

I'm wondering if there's a better way to do this, it seems ridiculous to decode the hex myself when there's an inbuilt function in socketcan_interface to do so. However, I was never able to get it to take f.data and compile successfully. Is it an internal only function? I'm not very familiar with C++ so the documentation wasn't clear.

I'm running ubuntu 14.04 and Indigo.