How to convert formatted string HH:MM:SS to seconds in C++

Question

I want to convert a string time stamp formatted in HH:MM:SS to seconds only, and then compare it with a number. I have written a prime version of my code in Java, however I separately ask from Scanner as opposed to having a string time. I'm not much familiar with C++ libraries, as I'm a Java guy. Wondering how I can do it in C++?

Make it brief, String s = "1:01:01"; and String s2= "3600"; I need to know if (s>s2)

import java.util.*;

public class Test {
    public static void main(String[] args) {
        Scanner console = new Scanner(System.in);

        int hours;
        int mins;
        int secs;

        System.out.println("Enter Hours: ");
        hours = console.nextInt();

        System.out.println("Enter Minutes: ");
        mins = console.nextInt();

        System.out.println("Enter Seconds: ");
        secs = console.nextInt();

        int showSecs = (hours * 3600) + (mins * 60) + secs;

        System.out.println(hours + ":" + mins + ":" + secs + " in secs are "
                + showSecs);

    }
}

Answer 1

I'll risk the downvotes and remind you that we still have sscanf in our toolbox.

int h, m, s= 0;
std::string time ="10:40:03"

if (sscanf(time.c_str(), "%d:%d:%d", &h, &m, &s) >= 2)
{
  int secs = h *3600 + m*60 + s;
}

Answer 2

As @ghostofstandardspast suggested you can use the std::get_time() I/O manipulator to read a specific time format from a std::istream

#include <iostream>
#include <sstream>
#include <locale>
#include <iomanip>
#include <ctime>

int main() {
    std::tm t;
    std::istringstream ss("1:01:01");
    ss >> std::get_time(&t, "%H:%M:%S");
    std::cout << "Total seconds: " 
              << t.tm_hour * 3600 + t.tm_min * 60 + t.tm_sec 
              << std::endl;
}

Here's a fully working sample using clang. Unfortunately I couldn't get this sample running using GCC 4.8.x, I'd guess it's not complete in this implementation. May be GCC 4.9.x supports this correctly.

---

As looking for an alternative (if you can't use a compiler supporting the complete current c++11 standard actually), you may either consider to use std::sscanf() as @Roddy suggested, or split the string using ':' as delimiter character, and simply convert the split out parts to integer values, using the e.g. the atoi() method.
Here's the alternative

#include <iostream>
#include <vector>
#include <string>
#include <sstream>

std::vector<std::string> &split
    ( const std::string &s
    , char delim
    , std::vector<std::string> &elems) 
{
    std::istringstream ss(s);
    std::string item;
    while (std::getline(ss, item, delim)) {
        elems.push_back(item);
    }
    return elems;
}

int main() {
    std::vector<std::string> parts;
    split("1:01:01",':',parts);
    if(parts.size() == 3) {
        int hour = std::atoi(parts[0].c_str());
        int min = std::atoi(parts[1].c_str());
        int sec = std::atoi(parts[2].c_str());
        std::cout << "Total seconds: " 
                  << hour * 3600 + min * 60 + sec 
                  << std::endl; 
    }
    return 0;
}

Answer 3

Let's do a simple automaton that parse your string:

#include <string>

int string2sec(const std::string& str) {
  int i = 0;
  int res = -1;
  int tmp = 0;
  int state = 0;

  while(str[i] != '\0') {
    // If we got a digit
    if(str[i] >= '0' && str[i] <= '9') {
      tmp = tmp * 10 + (str[i] - '0');
    }
    // Or if we got a colon
    else if(str[i] == ':') {
      // If we were reading the hours
      if(state == 0) {
        res = 3600 * tmp;
      }
      // Or if we were reading the minutes
      else if(state == 1) {
        if(tmp > 60) {
          return -1;
        }
        res += 60 * tmp;
      }
      // Or we got an extra colon
      else {
        return -1;
      }

      state++;
      tmp = 0;
    }
    // Or we got something wrong
    else {
      return -1;
    }
    i++;
  }

  // If we were reading the seconds when we reached the end
  if(state == 2 && tmp < 60) {
    return res + tmp;
  }
  // Or if we were not, something is wrong in the given string
  else {
    return -1;
  }
}

This has not been tested so there is no warranties.

EDIT: I still can not promise anything but I ran quick tests and it seems to work properly as expected.

#include <iostream>
int main(int argc, char** argv) {
  (void) argc;
  (void) argv;

  std::cout << string2sec("0:2:0") << std::endl;
  std::cout << string2sec("1:0:0") << std::endl;
  std::cout << string2sec("1:2:0") << std::endl;
  std::cout << string2sec("10:10:10") << std::endl;
  return 0;
}

Output:

120
3600
3720
36610