C++ String::compare() function

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The C++ std::string::compare() function is used to compare two strings. It provides a way to lexicographically compare the content of the string objects with another string or a sub string. It returns a integer that are listed below :

0: The strings are equal

<0: The calling string is less than the argument string.

> 0: The calling string is greater than the argument string.

This function can be used to compare the entire string or a specified range of characters.

Syntax

Following is the syntax for std::string::compare() function.

int compare (const string& str) const noexcept;
or
int compare (size_t pos, size_t len, const string& str) const;
int compare (size_t pos, size_t len, const string& str, size_t subpos, size_t sublen) const;
or
int compare (const char* s) const;
int compare (size_t pos, size_t len, const char* s) const;
or
int compare (size_t pos, size_t len, const char* s, size_t n) const;

Parameters

• str − It indicates the another string object.
• len − It indicates the length of the compared string.
• pos − It indicates the position of the first character in the corresponding string.
• subpos, sublen − same as pos and len above.
• n − It indicates the number of characters to compare.
• s − It indicates the pointer to an array of characters.

Return value

It returns a signed integral indicating the relation between the strings.

Exceptions

if an exception is thrown, there are no changes in the string.

Example 1

Following is the basic example to demonstrate the string::compare using C++.

#include 
#include 
using namespace std;
int main() {
   string X1 = "apple";
   string X2 = "banana";
   int result = X1.compare(X2);
   if (result == 0) {
      cout << " Both are equal " << endl;
   } else if (result < 0) {
      cout << X1 << " is less than " << X2 << endl;
   } else if (result > 0) {
      cout << X1 << " is greater than " << X2 << endl;
   }
   return 0;
}

Output

Let us compile and run the above program, this will produce the following result −

apple is less than banana

Example 2

In this example, we are comparing one substring with the another string. So it prints the output as equal.

#include 
#include 
using namespace std;
int main() {
   string X1 = "Tutorialspoint";
   string X2 = "point";
   int result = X1.compare(9, 5, X2);
   if (result == 0) {
      cout << " Both are equal " << endl;
   } else if (result < 0) {
      cout << X1.substr(6, 5) << " is less than " << X2 << endl;
   } else if (result > 0) {
      cout << X1.substr(6, 5) << " is greater than " << X2 << endl;
   }
   return 0;
}

Output

If we run the above code it will generate the following output.

Both string are equal.

Example 3

Following is an another example to compare substrings of two strings using string::compare() function.

#include 
#include 
using namespace std;
int main() {
   string X1 = "hello world";
   string X2 = "goodbye world";
   int result = X1.compare(6, 5, X2, 8, 5);
   if (result == 0) {
      cout << " Both are equal " << endl;
   } else if (result < 0) {
      cout << X1.substr(6, 5) << " is less than " << X2.substr(8, 5) << endl;
   } else {
      cout << X1.substr(6, 5) << " is greater than " << X2.substr(8, 5) << endl;
   }
   return 0;
}

Output

Following is the output of the above code.

The substrings are equal.                 

Example 4

In this example, we compare with one string with the empty string.

#include 
#include 
using namespace std;
int main() {
   string X1 = "hello";
   string X2 = "";
   int result = X1.compare(X2);
   if (result == 0) {
      cout << " Both are equal " << endl;
   } else if (result < 0) {
      cout << X1 << " is lesser than " << X2 << endl;
   } else {
      cout << X1 << " is greater than " << X2 << endl;
   }
   return 0;
}

Output

Following is the output of the above code.

hello is greater than