C++ Programming Code Examples
C++ > Visual C++ 5.0 Standard C++ Library Code Examples
Algorithm lexicographical compare - Lexicographically compare two sequences.
Algorithm lexicographical compare - Lexicographically compare two sequences.
lexicographical_compare
Header
<algorithm>
template<class InputIterator1, InputIterator2>
bool lexicographical_compare(InputIterator1 first1, InputIterator1 last1, InputIterator2 first2, InputIterator2 last2)
Lexicographically compare two sequences. The lexicographical comparison is a dictionary comparison in which words are compared for ordering. Compares two sequences [first1, last1) and [first2, last2) as follows: traverses the sequences, comparing corresponding pairs of elements e1 and e2: if e1 < e2, then return true. If e2 < e1, then return false, otherwise continue to the next corresponding pair of elements. If the first sequence gets exhausted but the second is not, return true, otherwise return false.
The non-predicate version uses operator== for comparison.
template<class InputIterator1, InputIterator2, class BinaryPredicate>
bool lexicographical_compare(InputIterator1 first1, InputIterator1 last1, InputIterator2 first2, InputIterator2 last2, BinaryPredicate pr)
Lexicographically compare two sequences. The lexicographical comparison is a dictionary comparison in which words are compared for ordering. Compares two sequences [first1, last1) and [first2, last2) as follows: traverses the sequences, comparing corresponding pairs of elements e1 and e2: if e1 < e2, then return true. If e2 < e1, then return false, otherwise continue to the next corresponding pair of elements. If the first sequence gets exhausted but the second is not, return true, otherwise return false.
The predicate version uses the predicate function pr for comparison.
Samples
#pragma warning (disable:4786)
#include <algorithm>
#include <iostream>
#include <string>
#include <cstring>
#include <functional>
int main()
{
std::string s1("Shaun"), s2("Shawn") ;
char *s3 = "Sammy" ;
char *s4 = "Sam" ;
int s3Len = strlen(s3) ;
int s4Len = strlen(s4) ;
bool result ;
//non-predicate version of lexicographical_compare
result = std::lexicographical_compare(s1.begin(), s1.end(), s2.begin(), s2.end()) ;
std::cout << "s1 = " << s1 << std::endl ;
std::cout << "s2 = " << s1 << std::endl ;
std::cout << "using non-predicate version of lexicographical_compare" << std::endl ;
if (result)
std::cout << "s1 < s2" << std::endl ;
else
std::cout << "s1 >= s2" << std::endl ;
//predicate version of lexicographical_compare
result = std::lexicographical_compare(s3, s3+s3Len, s4, s4+s4Len, std::less<char>()) ;
std::cout << "\n\ns3 = " << s3 << std::endl ;
std::cout << "s4 = " << s4 << std::endl ;
std::cout << "using non-predicate version of lexicographical_compare" << std::endl ;
if (result)
std::cout << "s3 < s4" << std::endl ;
else
std::cout << "s3 >= s4" << std::endl ;
return 0 ;
}
Program Output
s1 = Shaun
s2 = Shaun
using non-predicate version of lexicographical_compare
s1 < s2
s3 = Sammy
s4 = Sam
using non-predicate version of lexicographical_compare
s3 >= s4
Lexicographical less-than comparison. Returns true if the range [first1,last1) compares lexicographically less than the range [first2,last2). The C++ function std::algorithm::lexicographical_compare() tests whether one range is lexicographically less than another or not. A lexicographical comparison is the kind of comparison generally used to sort words alphabetically in dictionaries. A lexicographical comparison is the kind of comparison generally used to sort words alphabetically in dictionaries; It involves comparing sequentially the elements that have the same position in both ranges against each other until one element is not equivalent to the other. The result of comparing these first non-matching elements is the result of the lexicographical comparison. If both sequences compare equal until one of them ends, the shorter sequence is lexicographically less than the longer one.
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