Sorting dates (string) stored in vector

Question

I have a vector that contains dates in this format, DDMMMYY, e.g 12Jan14

vector<string> tempDate

When I use the STL sort, basically it will work when all of the dates are in the same year/month. 01Jan14, 05Jan14, 11Jan14, etc. But when I enter 02Feb14, it will all be messed up.

sort (tempDate.begin(), tempDate.end())

Can anyone tell me what went wrong with it?

Edit: I tried to use templates, but it doesn't work as all the string got 'split' up. I did some troubleshooting inside the sortDayMonthYear

template <class T>
bool sortDayMonthYear(T a, T b)
{
   for (int i =0; i < a.size(); i++)
       cout << a.at(i)<< endl;
}

What i get is something like this

0
1
J
A
N
1
4
0
2
J
A
N
1
4

Actually what I intend to do is to pass the two strings into the template function, using substr to get the day, month, year, compare and return true or false.

The string is not 'split-up', you're just outputting `endl` after each character. — Nemanja Boric, Jan 13 '14 at 15:50
Do you really need to store the strings in such an inconvenient format? The conventional "YYYYMMDD" is fairly readable to humans, and can simply be sorted lexicographically. — Mike Seymour, Jan 13 '14 at 15:52
One of the great and terrible things about C++ programs is that they do exactly what you tell them to do. There's no magic involved. `"Jan"` will never come before `"Aug"`. — John Dibling, Jan 13 '14 at 15:58
Thanks for the reply people. The expected output when i cout << a.at(i)<< endl; should be 01Jan14. Not just 0. @NemanjaBoric — user3001342, Jan 13 '14 at 15:58
I'm sorry that was a mistake, I thought i'm passing the whole vector into the function. Silly mistake. Appreciate all the replies. — user3001342, Jan 13 '14 at 16:03

score 3 · Answer 1 · answered Jan 13 '14 at 15:51

Your predicate should take two constant string references as argument, and then use those to decide which one is "lesser" than the other.

So:

bool sortDayMonthYear(const std::string& first, const std::string& second)
{
    // Algorithm to find out which string is "lesser" than the other
}

Then you use that comparator function when sorting:

std::sort(std::begin(tempDate), std::end(tempDate), sortDayMonthYear);

score 2 · Answer 2 · edited May 23 '17 at 12:00

2

The standard way of sorting strings is lexicographical (by alphabet, for each letter, just like in a dictionary).

Therefore, what you need is your own comparator. There is a version of sort which takes one as third parameter. See e.g. this question for starting ideas: Sorting a vector of custom objects

edited May 23 '17 at 12:00

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answered Jan 13 '14 at 15:50

codeling

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Sorting dates (string) stored in vector

2 Answers2