How to use the lexicographical_compare() in the C++

Hello, I am studying in the first year of the Msc. I have the basic knowledge of the C++ language. I also have the knowledge about the functions in the C++ language. But I do not know anything about the lexicographical_compare() function of C++ language. So, I would like to know about the lexicographical_compare() function. I also would like to know about the how to use the lexicographical_compare() function in the C++ language. Reply Me.

Hi, The lexicographical_compare() function can be used in the C++ language to show the less than comparison lexicographically. The lexicographical_compare() function can returns the true value if the given specified range as [fst1,lst1) can be compares lexicographically less than that the range that can be [fst2,lst2). The following can be the syntax of the lexicographical_compare() function :

Code:

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template <class InptItrtr1, class InptItrtr2>
  bool lexicographical_compare ( InptItrtr1 fst1, InptItrtr1 lst1,
                                InptItrtr2 fst2, InptItrtr2 lst2 );

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The following can be the one more example on the lexicographical_compare() function that demonstrates you how the lexicographical_compare() function can be used in the C++ language :

Code:

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#include <iostream>
#include <algorithm>
#include <cctype>
using namespace std;
bool mcmp (char d1, char d2)
{
 return tolower(d1)<tolower(d2);
}
int main ()
{
  char ft[]="Apple";     
  char sn[]="apartment";
  cout << "Using default comparison (operator<): ";
  if (lexicographical_compare(ft,ft+5,sn,sn+9))
    cout << ft << " is less than " << sn << endl;
  else
    if (lexicographical_compare(sn,sn+9,ft,ft+5))
      cout << ft << " is greater than " << sn << endl;
  else
    cout << ft << " and " << sn << " are equivalent\n";
  cout << "Using mcmp as comparison object: ";
  if (lexicographical_compare(ft,ft+5,sn,sn+9,mcmp))
    cout << ft << " is less than " << sn << endl;
  else
    if (lexicographical_compare(sn,sn+9,ft,ft+5,mcmp))
      cout << ft << " is greater than " << sn << endl;
  else
    cout << ft << " and " << sn << " are equivalent\n";
  return 0;
}

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Output:

Code:

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Using default comparison (operator<): Apple is less than apartment
Using mcmp as comparison object: Apple is greater than apartment

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The following can be the parameters of the lexicographical_compare() function in the C++ language :
1. fst2, lst2 : These parameters can be used in the C++ language for an input iterators to the final and starting positions of the given specified second sequence. The range used can be as [fst2,lst2).
2. fst1, lst1 : These parameters can be used in the C++ language for an input iterators to the final and starting positions of the given specified first sequence. The range used can be as [fst1,lst1) that can contains all of an elements that can be between fst1 and lst1.

The lexicographical_compare() function can returns the true value if the given specified range of an elements as [strt1,nd1) can be lexicographically less than the given range of an elements as [strt2,nd2). If you can be confused about what a lexicographic means then the a lexicographic means lexicographic can might help you to know that the dictionaries can be ordered lexicographically. The lexicographical_compare() function can be runs in a linear time.

The code of lines that can be mentioned below gives you the knowledge about the lexicographical_compare() function :

Code:

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using std::lexicographical_compare;
int main()
{
  int B1[] = {3, 1, 4, 1, 5, 9, 3};
  int B2[] = {3, 1, 4, 2, 8, 5, 7};
  int B3[] = {1, 2, 3, 4};
  int B4[] = {1, 2, 3, 4, 5};
  const int M1 = sizeof(B1) / sizeof(int);
  const int M2 = sizeof(B2) / sizeof(int);
  const int M3 = sizeof(B3) / sizeof(int);
  const int M4 = sizeof(B4) / sizeof(int);
  bool D12 = lexicographical_compare(B1, B1 + M1, B2, B2 + M2);
  bool D34 = lexicographical_compare(B3, B3 + M3, B4, B4 + M4);
  cout << "B1[] < B2[]: " << (D12 ? "true" : "false") << endl;
  cout << "B3[] < B4[]: " << (D34 ? "true" : "false") << endl;
}
int main()
{
  bool D12 = std::lexicographical_compare(B1, B1 + M1, B2, B2 + M2);
  bool D34 = std::lexicographical_compare(B3, B3 + M3, B4, B4 + M4);
}

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