lexicographical_compare


Category: algorithms 
Component type: function 
Prototype
Lexicographical_compare is an overloaded name; there are actually
two lexicographical_compare functions.
template <class InputIterator1, class InputIterator2>
bool lexicographical_compare(InputIterator1 first1, InputIterator1 last1,
InputIterator2 first2, InputIterator2 last2);
template <class InputIterator1, class InputIterator2, class BinaryPredicate>
bool lexicographical_compare(InputIterator1 first1, InputIterator1 last1,
InputIterator2 first2, InputIterator2 last2,
BinaryPredicate comp);
Description
Lexicographical_compare returns true if the range of elements
[first1, last1) is lexicographically less than the range of
elements [first2, last2), and false otherwise. Lexicographical
comparison means "dictionary" (elementbyelement) ordering. That is,
[first1, last1) is less than [first2, last2) if *first1 is
less than *first2, and greater if *first1 is greater than *first2.
If the two first elements are equivalent then lexicographical_compare
compares the two second elements, and so on. As with ordinary
dictionary order, the first range is considered to be less than
the second if every element in the first range is equal to the
corresponding element in the second but the second contains more elements.
The two versions of lexicographical_compare differ in how they define whether one
element is less than another. The first version compares
objects using operator<, and the second compares objects using
a function object comp.
Definition
Defined in the standard header algorithm, and in the nonstandard
backwardcompatibility header algo.h.
Requirements on types
For the first version:

InputIterator1 is a model of Input Iterator.

InputIterator2 is a model of Input Iterator.

InputIterator1's value type is a model of LessThan Comparable.

InputIterator2's value type is a model of LessThan Comparable.

If v1 is an object of InputIterator1's value type and v2
is an object of InputIterator2's value type, then both v1 < v2
and v2 < v1 are defined.
For the second version:

InputIterator1 is a model of Input Iterator.

InputIterator2 is a model of Input Iterator.

BinaryPredicate is a model of Binary Predicate.

InputIterator1's value type is convertible to BinaryPredicate's
first argument type and second argument type.

InputIterator2's value type is convertible to BinaryPredicate's
first argument type and second argument type.
Preconditions

[first1, last1) is a valid range.

[first2, last2) is a valid range.
Complexity
Linear. At most 2 * min(last1  first1, last2  first2) comparisons.
Example
int main()
{
int A1[] = {3, 1, 4, 1, 5, 9, 3};
int A2[] = {3, 1, 4, 2, 8, 5, 7};
int A3[] = {1, 2, 3, 4};
int A4[] = {1, 2, 3, 4, 5};
const int N1 = sizeof(A1) / sizeof(int);
const int N2 = sizeof(A2) / sizeof(int);
const int N3 = sizeof(A3) / sizeof(int);
const int N4 = sizeof(A4) / sizeof(int);
bool C12 = lexicographical_compare(A1, A1 + N1, A2, A2 + N2);
bool C34 = lexicographical_compare(A3, A3 + N3, A4, A4 + N4);
cout << "A1[] < A2[]: " << (C12 ? "true" : "false") << endl;
cout << "A3[] < A4[]: " << (C34 ? "true" : "false") << endl;
}
Notes
See also
equal, mismatch,
lexicographical_compare_3way,
search,
LessThan Comparable,
Strict Weak Ordering,
sort
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