Parsing a date string in C++ - c++

Question

My son is learning C++ and one of his exercises it to have the user input a date in DD/MM/YYY and then output it to Month day, year
So: 19/02/2013
Output: February 19, 2013.
I am trying to help him understand the various ways but now I have confused myself.
getline()
std::string::substr()
std::string::find()
std::string::find_first_of()
std::string::find_last_of()
I can't figure it out with any of these quite right.
my current attempt to parse is:
#include <iostream>
#include <string>
using namespace std;
int main (void)
{
string date;
string line;
cout << "Enter a date in dd/mm/yyyy format: " << endl;
std::getline (std::cin,date);
while (getline(date, line))
{
string day, month, year;
istringstream liness( line );
getline( liness, day, '/' );
getline( liness, month, '/' );
getline( liness, year, '/' );
cout << "Date pieces are: " << day << " " << month << " " << year << endl;
}
}
but I am getting errors like:
`g++ 3_12.cpp -o 3_12`
`3_12.cpp: In function ‘int main()’:`
`3_12.cpp:16: error: cannot convert ‘std::string’ to ‘char**’ for argument ‘1’ to ‘ssize_t getline(char**, size_t*, FILE*)’`
`3_12.cpp:18: error: variable ‘std::istringstream liness’ has initializer but incomplete type`

Answer 1

int day, month, year;
char t;
std::cin >> day >> t >> month >> t >> year;

Answer 2

You've missed the std Regular Expressions Library! I reckon it's the safest and most effective way of doing this.
Back on topic, I think that since getline is an extern "C" function, you can't overload it using a using namespace std (which should be banned by the way). You should try prepending std to all getline calls.

Answer 3

For std::istringstream, you need:
#include <sstream>
P.S. Don't use using namespace std;. It's a bad habit, and it will eventually get you into trouble.

Answer 4

The error
3_12.cpp:16: error: cannot convert ‘std::string’ to ‘char**’ for argument ‘1’ to ‘ssize_t getline(char**, size_t*, FILE*)’
means the compiler couldn't make sense of this line:
while (getline(date, line))
Both date and line are declared as std::string and there's no overload of getline that
takes two strings. Compiler guessed that you were trying to call this function that is not part of C++ library (apparently, one of standard library headers includes stdio.h which is where that function is coming from).
The error
3_12.cpp:18: error: variable ‘std::istringstream liness’ has initializer but incomplete type
means the compiler doesn't know what std::istringstream is. You forgot to include <sstream>.
If you want to extract lines from a string by means of std::getline, you need to put it in a stringstream first, just like you do inside the loop.
Parsing dates isn't that easy. You don't want the user to be able to enter 44/33/-200 and get away with it. How I'd might approach this:
std::istringstream iss(date); // date is the line you got from the user
unsigned int day, month, year;
char c1, c2;
if (!(iss >> day >> c1 >> month >> c2 >> year)) {
// error
}
if (c1 != '/' || c2 != '/') { /* error */ }
if (month > 12) { /* error / }
// ... more of that, you get the idea