Using parallel_sort algorithm on a struct

Question

How to use parallel_sort with this struct:

struct d
{
    char name[5];
};

struct less_than_key
{
    inline bool operator() (const d& struct1, const d& struct2) const
    {
        return strcmp(struct1.name, struct2.name) == -1;
    }
};

vector<d> my_d;
my_d.resize(3);

strcpy(my_d[0].name, "mike");
strcpy(my_d[1].name, "joe");
strcpy(my_d[2].name, "anna");

parallel_sort(my_d.begin(), my_d.end(), less_than_key());

DONE!, I hope this helps someone else.

Guess it's time to take my Phd in sorting algorithms!

The error is clearly visible. Go check the interface of vector, and if you still don't have a clue, consider following the advice in my first comment. — Griwes, Dec 14 '13 at 11:54
I'm still going to tell you to use std::string instead of char arrays. It makes code initialisations like these so much safer and more elegant. — , Dec 14 '13 at 11:56
@polkadotcadaver: i see your point, i will seriously consider it... — SkyRipper, Dec 14 '13 at 11:58
did the code above made any progress (but still doesn't work...) — SkyRipper, Dec 14 '13 at 11:58
Your struct needs an `operator<` that implements strict weak ordering. Assuming you do that then `parallel_sort(my_d.begin(), my_d.end());` should work. — Retired Ninja, Dec 14 '13 at 12:08
http://stackoverflow.com/questions/1380463/sorting-a-vector-of-custom-objects — Retired Ninja, Dec 14 '13 at 12:28
You do realize your sort is comparing the address of the literal strings in memory and not the content of the strings themselves right? — Retired Ninja, Dec 15 '13 at 02:57

score 2 · Accepted Answer · answered Dec 14 '13 at 12:27

2

Don't use C-style strings when you can easily use std::string.

Since your struct only contains a string you may want to just use std::string instead (which implements the operators that you need for parallel_sort to work).

std::vector<std::string> vec(3);
vec.emplace_back("mike");
vec.emplace_back("joe");
vec.emplace_back("anna");

and then, following the function signature, you just need to find the begin and end iterator:

parallel_sort(std::begin(vec), std::end(vec));

answered Dec 14 '13 at 12:27

Shoe

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thanks a lot for the suggestion, but can you help me do it with chars, please? – SkyRipper Dec 14 '13 at 12:42
I tried and made my code almost correct – SkyRipper Dec 14 '13 at 12:43
@SkyRipper, why do you want it with chars? – Shoe Dec 14 '13 at 13:15
For performance reasons(I know it's very little, but the little counts and I have many data) – SkyRipper Dec 14 '13 at 13:16
Based on how hard it was for you to figure out how this works at all I feel like you didn't profile both solutions to see which was faster and just assume, most likely incorrectly, that bare character arrays are faster. – Retired Ninja Dec 15 '13 at 02:59

Using parallel_sort algorithm on a struct

1 Answers1