Difference between revisions of "cpp/algorithm/lexicographical compare"
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{{param list item | first1, last1 | the first range of elements to examine}} | {{param list item | first1, last1 | the first range of elements to examine}} | ||
{{param list item | first2, last2 | the second range of elements to examine}} | {{param list item | first2, last2 | the second range of elements to examine}} | ||
| − | {{param list cmp | comp | p1=InputIt1 | p2=InputIt2}} | + | {{param list cmp | comp | p1=InputIt1 | p2=InputIt2}} |
| + | {{param list hreq}} | ||
| + | {{param list req concept | InputIt1, InputIt2 | InputIterator}} | ||
{{param list end}} | {{param list end}} | ||
Revision as of 04:44, 3 August 2012
Template:ddcl list begin <tr class="t-dsc-header">
<td><algorithm>
<td></td> <td></td> </tr> <tr class="t-dcl ">
<td >bool lexicographical_compare( InputIt1 first1, InputIt1 last1,
<td > (1) </td> <td class="t-dcl-nopad"> </td> </tr> <tr class="t-dcl ">
<td >bool lexicographical_compare( InputIt1 first1, InputIt1 last1,
InputIt2 first2, InputIt2 last2,
<td > (2) </td> <td class="t-dcl-nopad"> </td> </tr> Template:ddcl list end
Checks if the first range [first1, last1) is lexicographically less than the second range [first2, last2). The first version uses operator< to compare the elements, the second version uses the given comparison function comp.
Lexicographical comparison is a operation with the following properties:
- Two ranges are compared element by element.
- The first mismatching element defines which range is lexicographically less or greater than the other.
- If one range is a prefix of another, the shorter range is lexicographically less than the other.
- If two ranges have equivalent elements and are of the same length, then the ranges are lexicographically equal.
- An empty range is lexicographically less than any non-empty range.
- Two empty ranges are lexicographically equal.
Contents |
Parameters
| first1, last1 | - | the first range of elements to examine |
| first2, last2 | - | the second range of elements to examine |
| comp | - | comparison function object (i.e. an object that satisfies the requirements of Compare) which returns true if the first argument is less than the second. The signature of the comparison function should be equivalent to the following: bool cmp(const Type1& a, const Type2& b); While the signature does not need to have const&, the function must not modify the objects passed to it and must be able to accept all values of type (possibly const) |
| Type requirements | ||
-InputIt1, InputIt2 must meet the requirements of LegacyInputIterator.
| ||
Return value
true if the first range is lexicographically less than the second.
Complexity
At most 2·min(N1, N2) applications of the comparison operation, where N1 = std::distance(first1, last1) and N2 = std::distance(first2, last2).
Possible implementation
| First version |
|---|
template<class InputIt1, class InputIt2> bool lexicographical_compare(InputIt1 first1, InputIt1 last1, InputIt2 first2, InputIt2 last2) { for ( ; (first1 != last1) && (first2 != last2); first1++, first2++ ) { if (*first1 < *first2) return true; if (*first2 < *first1) return false; } return (first1 == last1) && (first2 != last2); } |
| Second version |
template<class InputIt1, class InputIt2, class Compare> bool lexicographical_compare(InputIt1 first1, InputIt1 last1, InputIt2 first2, InputIt2 last2, Compare comp) { for ( ; (first1 != last1) && (first2 != last2); first1++, first2++ ) { if (comp(*first1, *first2)) return true; if (comp(*first2, *first1)) return false; } return (first1 == last1) && (first2 != last2); } |
Example
| This section is incomplete Reason: no example |
