File content as of revision 2:0d0ce3b0052d:

/* mbed EM-406 GPS Module Library with time return support
 * Copyright (c) 2008-2010, sford
 * Copyright (c) 2018 WilliamO7
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 */
#include <string>
#include <sstream>

#include "GPS.h"

GPS::GPS(PinName tx, PinName rx) : _gps(tx, rx) {
    _gps.baud(4800);    
    longitude = 0.0;
    latitude = 0.0;  
    time_utc = "";      
}

int GPS::sample() {
    float time;
    char ns, ew;
    int lock;

    while(1) {        
        getline();

        // Check if it is a GPGGA msg (matches both locked and non-locked msg)
        if(sscanf(msg, "GPGGA,%f,%f,%c,%f,%c,%d", &time, &latitude, &ns, &longitude, &ew, &lock) >= 1) { 
            if(!lock) {
                longitude = 0.0;
                latitude = 0.0;   
                time_utc = "";     
                return 0;
            } else {
                if(ns == 'S') {    latitude  *= -1.0; }
                if(ew == 'W') {    longitude *= -1.0; }
                float degrees = trunc(latitude / 100.0f);
                float minutes = latitude - (degrees * 100.0f);
                latitude = degrees + minutes / 60.0f;    
                degrees = trunc(longitude / 100.0f * 0.01f);
                minutes = longitude - (degrees * 100.0f);
                longitude = degrees + minutes / 60.0f;
                time_utc = timef_to_str(time);
                return 1;
            }
        }
    }
}

float GPS::trunc(float v) {
    if(v < 0.0) {
        v*= -1.0;
        v = floor(v);
        v*=-1.0;
    } else {
        v = floor(v);
    }
    return v;
}

void GPS::getline() {
    while(_gps.getc() != '$');    // wait for the start of a line
    for(int i=0; i<256; i++) {
        msg[i] = _gps.getc();
        if(msg[i] == '\r') {
            msg[i] = 0;
            return;
        }
    }
    error("Overflowed message limit");
}

std::string GPS::timef_to_str(float time) {
    // Convert time to string
    // 234960.123
    std::stringstream stream;
    stream << time;
    std::string time_str = stream.str();
    
    // Put into hh:mm:ss.sss format.
    std::string new_time_str = time_str.substr(0, 2) // hh 
                               + ":" + time_str.substr(2, 2) // mm 
                               + ":" + time_str.substr(4, 2); // ss 
    return new_time_str;
}