Simple std::sort not working

Question

I have the following code:

int main()
{
    int intArr[] = { 1,5,3 };
    //auto f = [](auto a, auto b) {return a < b;};
    //std::sort(intArr, intArr + 2, f);
    std::sort(intArr, intArr + 2);
    for (int& temp : intArr)
        cout << temp << endl;
}

However, the output is unsorted (e.g. the output is 1 5 3). The same result when using std::sort with lambda. What is causing this behavior?

I am using Visual C++ compiler (Visual Studio 2015).

http://stackoverflow.com/questions/5897319/how-to-use-stdsort-to-sort-an-array-in-c — juanchopanza, Nov 16 '15 at 12:37
That may not be a fancy question, and neither will make it into the hall of fame nor yield great rep gain for answerers, but it **is** a valid and well-formulated question; thus there's no reason to down-vote it. — decltype_auto, Nov 16 '15 at 12:49
Just reading documentation for `std::sort` would answer this question. — , Nov 16 '15 at 13:00
@Satus : It is a very reasonable mistake to assume that you have to include point till the last element, and not its end as well. And many other non-downvoted (even upvoted) questions on the site can be solved with much less effort than that. All I'm saying is that this question showed enough effort, a well curated example, and enough information. — therainmaker, Nov 16 '15 at 14:18
@therainmaker It is even more reasonable to read documentation of some library function before you post a question about it. And the fact that "many other non-downvoted (even upvoted) questions on the site can be solved with much less effort than that" is not a justification for not downvoting the questing, but a problem of stackoverflow as a question-answer platform. — , Nov 16 '15 at 14:28

101010 · Accepted Answer · 2015-11-16T12:58:51.500

7

In STL algorithms that take ranges, if you want to provide the whole range you have to give as ending an element one-past-the-end and not the end of the range itself, thus in your case:

std::sort(intArr, intArr + 3);

Or

std::sort(intArr, intArr + sizeof(intArr) / sizeof(int));

Or even better:

std::sort(std::begin(intArr), std::end(intArr));

edited Nov 16 '15 at 12:58

answered Nov 16 '15 at 12:36

101010

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Surely `sizeof(intArr)/sizeof(intArr[0])`? Which is exactly why the `std::end` version is better; avoids all sorts of common mistakes! – Andrew Nov 16 '15 at 12:57
@Andrew Never debug while standing up. Thanx corrected. – 101010 Nov 16 '15 at 12:59

score 2 · Answer 2 · answered Nov 16 '15 at 12:36

2

You have 3 values in array, but send only 2 (since in STL algorithms second parameter is past-end iterator). Should be

std::sort(intArr, intArr + 3);

answered Nov 16 '15 at 12:36

ForEveR

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Simple std::sort not working

2 Answers2