c++ - Custom is_sorted function template -

i want write own is_sorted function template implementation instead of using std::is_sorted. give me idea how it? want use arrays. want make declaration this:

template <typename t, size_t n> bool is_sorted (const t (&array)[n]); ,   bool operator>(const &, const &); declared. 

the obvious way compare each item 1 after it, , see if it's <= one.

you don't want directly though. first of all, sorting, client typically required ensure a < b defined, want use < instead of <=. second, want allow (but not require) user pass comparator of own, in case < isn't defined directly type or desired sort uses different criteria < defines.

as such, want define 2 versions of is_sorted, 1 using < directly, other using comparator passed user.

#include <iterator> #include <functional>  template <class init> bool is_sorted(init b, init e) {     if (b == e)           // no items -- sorted definition         return true;      typename std::iterator_traits<init>::value_type first = *b;     ++b;     while (b != e) {    // skip if e-b == 1 (single item sorted)         if (*b < first)             return false;         first = *b;         ++b;     }     return true; }  template <class init, class cmp> bool is_sorted(init b, init e, cmp cmp) {      if (b == e)         return true;      typename std::iterator_traits<init>::value_type first = *b;     ++b;     while (b != e) {    // skip if e-b == 1 (single item sorte)         if (cmp(*b, first))             return false;         first = *b;         ++b;     }     return true; } 

to keep myself honest, bit of test code, sorted, unsorted, identical, , reversed elements, using std::vector, std::deque, std::array, , built-in array:

#ifdef test #include <array> #include <vector> #include <iostream> #include <deque>  int main() {      std::vector<int> sorted{1, 2, 3, 4, 6, 100};     std::deque<int> unsorted{1, 5, 2, 7, 4};     std::array<int, 7> ident = {1, 1, 1, 1, 1, 3, 3};     int rev[] = {5, 4, 3, 2, 1};      if (!is_sorted(std::begin(sorted), std::end(sorted)))         std::cout << "sorted array detected un-sorted\n";     if (is_sorted(std::begin(unsorted), std::end(unsorted)))         std::cout << "un-sorted array detected sorted\n";     if (!is_sorted(std::begin(ident), std::end(ident)))         std::cout << "sorted array duplicated detected un-sorted\n";     if (!is_sorted(std::begin(rev), std::end(rev), std::greater<int>()))         std::cout << "reverse sorted array detected un-sorted\n";     return 0; } #endif 

this works fine me gcc 4.7.2. is_sorted code seems work fine vc++ 2012 (though test code requires minor modifications, e.g., eliminate use of uniform initialization, doesn't support yet).

edit: if don't mind tighter requirement on iterators (forward iterators instead of input iterators), can make code simpler , more efficient. example, code can reduced this:

template <class fwdit> bool is_sorted(fwdit b, fwdit e) {     if (b == e)           // no items -- sorted definition         return true;      (fwdit first = b; ++b != e; first = b)          if (*b < *first)             return false;         return true; }