Thread: Taking integers from a string

  1. #1
    Registered User
    Join Date
    May 2004
    Posts
    2

    Taking integers from a string

    Hello, this is my first question on this site. I have a string with a date in it, like "17/02/1943", in the format dd/mm/yyyy. I need to get the date from this string, and put it into my Date struct, which has three int's for Day, Month and Year. How would I go about getting the numbers out, would I get substrings and cast them or something?

  2. #2
    Registered User hk_mp5kpdw's Avatar
    Join Date
    Jan 2002
    Location
    Northern Virginia/Washington DC Metropolitan Area
    Posts
    3,817
    There are a couple different ways... The first involves using the atoi function:
    Code:
    #include <string>
    #include <iostream>
    #include <cstdlib>
    using namespace std;
    
    int main()
    {
        string str("14/05/1988");
        int day, month, year;
    
        day = atoi( str.substr(0,2).c_str() );
        month = atoi( str.substr(3,2).c_str() );
        year = atoi( str.substr(6,4).c_str() );
    
        cout << "Day: " << day << " Month: " << month << " Year: " << year << endl;
    
        return 0;
    }
    Or you can use string streams:
    Code:
    #include <iostream>
    #include <string>
    #include <sstream>
    using namespace std;
    
    int main()
    {
        string str("14/05/1988");
        int day, month, year;
        istringstream sstr(str);
        char dummy;
    
        sstr >> day >> dummy >> month >> dummy >> year;
    
        cout << "Day: " << day << " Month: " << month << " Year: " << year << endl;
    
        return 0;
    }
    Both ways should output the same thing:
    Code:
    Day: 14 Month: 5 Year: 1988
    "Owners of dogs will have noticed that, if you provide them with food and water and shelter and affection, they will think you are god. Whereas owners of cats are compelled to realize that, if you provide them with food and water and shelter and affection, they draw the conclusion that they are gods."
    -Christopher Hitchens

  3. #3
    Registered User
    Join Date
    May 2004
    Posts
    2
    Not too sure about that istringstream thing, and our lecturer looks down on anyone who uses C-style libraries or functions (i.e. cstdlib.h, cstring.h).

    I can get the substrings to just have the number I want ("32"), but can't convert them to int format. <static_cast><int> just gives me heaps of errors.

    Here's my code, Date is a struct:

    Code:
    #include <iostream>
    #include <string>
    #include "Date.h"
    
    using std::cout;
    using std::string;
    
    Date fileInputDate(string entry)
    {
    	Date output;
    	output.Day = static_cast<int>(entry.substr(0,2));
    	output.Month = static_cast<int>(entry.substr(3,2));
    	output.Year = static_cast<int>(entry.substr(6,4));
    	return output;
    }
    This gives me 3 C2440 errors. Is there anyway to do this without using C-style commands or any other libraries?

  4. #4
    Registered User
    Join Date
    May 2004
    Posts
    127
    >Is there anyway to do this without using C-style commands or any other libraries?
    You could always do the conversion manually. For small numbers like those in a date, you don't need to worry about the problematic cases that more sophisticated string-to-integer libraries must consider. The conversion is a simple loop.
    Code:
    Date fileInputDate(string entry)
    {
      Date output; // Assumes that output is zero initialized
    
      for (int i = 0; i < 2; i++) {
        output.Day = 10 * output.Day + (entry[i] - '0');
      }
      for (int i = 3; i < 5; i++) {
        output.Month = 10 * output.Month + (entry[i] - '0');
      }
      for (int i = 6; i < 10; i++) {
        output.Year = 10 * output.Year + (entry[i] - '0');
      }
    
      return output;
    }

Popular pages Recent additions subscribe to a feed

Similar Threads

  1. Replies: 8
    Last Post: 04-25-2008, 02:45 PM
  2. String issues
    By The_professor in forum C++ Programming
    Replies: 7
    Last Post: 06-12-2007, 09:11 AM
  3. Calculator + LinkedList
    By maro009 in forum C++ Programming
    Replies: 20
    Last Post: 05-17-2005, 12:56 PM
  4. Classes inheretance problem...
    By NANO in forum C++ Programming
    Replies: 12
    Last Post: 12-09-2002, 03:23 PM
  5. creating class, and linking files
    By JCK in forum C++ Programming
    Replies: 12
    Last Post: 12-08-2002, 02:45 PM