C++ <cstring> - strcmp() Function

The C++ <cstring> strcmp() function is used to compare two null-terminated byte strings lexicographically. The function starts comparing the first pair of characters of each string and continues comparing until the pair of characters are different or until a terminating null-character is reached.

Syntax

int strcmp ( const char * lhs, const char * rhs );

Parameters

`lhs`	Specify pointer to the first null-terminated byte string to compare.
`rhs`	Specify pointer to the second null-terminated byte string to compare.

Return Value

Based on the value of lhs and rhs, the function returns the following:

Negative value if lhs appears before rhs in lexicographical order.
Zero if lhs and rhs compare equal.
Positive value if lhs appears after rhs in lexicographical order.

Example: Value returned by function = 0

The example below shows the usage of strcmp() function.

#include <iostream>
#include <cstring>
using namespace std;
 
int main (){
  char str1[20] = "Hello";
  char str2[20] = "Hello";
  
  //comparing str1 and str2
  int retval = strcmp(str1, str2);

  //displaying the result
  if(retval != 0)
    cout<<"str1 and str2 are not equal.\n";
  else
    cout<<"str1 and str2 are equal.\n";
 
  cout<<"Value returned by the function: "<<retval<<"\n";

  return 0;
}

The output of the above code will be:

str1 and str2 are equal.
Value returned by the function: 0

Example: Value returned by function < 0

Lets consider this example where the returned value is less than zero.

#include <iostream>
#include <cstring>
using namespace std;
 
int main (){
  char str1[20] = "Hello";
  char str2[20] = "World";
  
  //comparing str1 and str2
  int retval = strcmp(str1, str2);

  //displaying the result
  if(retval != 0)
    cout<<"str1 and str2 are not equal.\n";
  else
    cout<<"str1 and str2 are equal.\n";

  cout<<"Value returned by the function: "<<retval<<"\n";

  return 0;
}

The output of the above code will be:

str1 and str2 are not equal.
Value returned by the function: -15

Example: Value returned by function > 0

Lets consider another example where the returned value is greater than zero.

#include <iostream>
#include <cstring>
using namespace std;
 
int main (){
  char str1[20] = "Hello";
  char str2[20] = "Apple";
  
  //comparing str1 and str2
  int retval = strcmp(str1, str2);

  //displaying the result
  if(retval != 0)
    cout<<"str1 and str2 are not equal.\n";
  else
    cout<<"str1 and str2 are equal.\n";

  cout<<"Value returned by the function: "<<retval<<"\n";

  return 0;
}

The output of the above code will be:

str1 and str2 are not equal.
Value returned by the function: 7

❮ C++ <cstring> Library