Книга: Standard Template Library Programmer

lexicographical_compare

lexicographical_compare

Category: algorithms

Component type: function

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);

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" (element-by-element) 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.

Defined in the standard header algorithm, and in the nonstandard backward-compatibility header algo.h.

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.

• [first1, last1) is a valid range.

• [first2, last2) is a valid range.

Linear. At most 2 * min(last1 – first1, last2 – first2) comparisons.

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;
}

equal, mismatch, lexicographical_compare_3way, search, LessThan Comparable, Strict Weak Ordering, sort

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