fast kth element of sorted array implementation

Question

I'm trying to understand this algorithm from J.F. Sebastian, but I try to compile it (gcc/g++ 4.8) get a strange compiler error:

const int n=101,m=31,k=*16-1;
int i;
srand(time(NULL));
for(i=0;i<n;i++)    x[i]=rand();
std::sort(x,x+m,std::greater<float>());
std::sort(x+m,x+n,std::greater<float>());
float v=nsmallest_iter(x,x+m,x+m+1,x+n,n-1-k,std::greater<float>());

Edit

adding the -std=c++11 flag I get:

  from blabla.cpp:2:
blabla.cpp: In instantiation of ‘typename std::iterator_traits<_Iterator>::value_type nsmallest_iter(RandomAccessIterator, RandomAccessIterator, RandomAccessIterator, RandomAccessIterator, size_t, Compare) [with RandomAccessIterator = float*; Compare = std::greater<float>; typename std::iterator_traits<_Iterator>::value_type = float; size_t = long unsigned int]’:
blabla.cpp:58:64:   required from here
blabla.cpp:28:66: error: ‘issorted’ was not declared in this scope
  assert(issorted(firsta,lasta,less) && issorted(firstb,lastb,less));
                                                                  ^
blabla.cpp:28:35: error: ‘issorted’ was not declared in this scope, and no declarations were found by argument-dependent lookup at the point of instantiation [-fpermissive]
  assert(issorted(firsta,lasta,less) && issorted(firstb,lastb,less));
                                   ^
blabla.cpp:28:66: note: ‘issorted’ declared here, later in the translation unit
  assert(issorted(firsta,lasta,less) && issorted(firstb,lastb,less));
                                                              ^

Anybody knows how to fix this?

you should consider to create a new question if you do in fact have a new problem ;) — Theolodis, May 12 '14 at 07:46
@Jarod42: thanks, if you would post your comment as an answer, i'd be happy to accept it: it solved the problem! — user189035, May 12 '14 at 07:52

Theolodis · Answer 1 · 2014-05-12T07:53:18.487

1

You are using a C++11 feature, so you have to either use the compile flag

-std=c++11

or

-std=c++0x

for the second problem you are probably missing some header or do have an issue with the code.

edit: issorted does probably refer to std::is_sorted. It is to be found in the include #include <algorithm>

edited May 12 '14 at 07:53

answered May 12 '14 at 07:45

Theolodis

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score 0 · Accepted Answer · answered May 12 '14 at 09:12

0

Replace issorted by std::is_sorted.
(Add #include <algorithm> if not present)
(Compile with C++11)

answered May 12 '14 at 09:12

Jarod42

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fast kth element of sorted array implementation

Edit

2 Answers2