C++ strcmp() method

The strcmp() is a string manipulation function defined in the cstring header file, which works on a string which is stored in a c-style char array and and it is used copy the compare the characters of two strings.

Signature of strcmp() function

int strcmp ( const char * str1, const char * str2 )

This function compares the characters of str1 string to another string str2 and returns the result of comparison in the form an int value, such as -

int value	description
0	when characters in two strings are the same.
1	when the non-matching character in the first string is having an ASCII* value larger than the character at the same index in second string.*
-1	when the non-matching character in the first string is having an ASCII* value smaller than the character at the same index in second string.*

Example of strcmp() function

strcmp()

char[]

The first char[] array i.e. first is initialized with a string value Welcome
The second char[] array i.e. second is also initialized with the same value Welcome.
The third char[] array i.e. third is initialized with the value welcome, starting with the lower case w.

// strcmp example 

#include<iostream>
#include<cstring>

using namespace std;

int main()
{
char first[10] = "Welcome";
char second[10] = "Welcome";
char third[10] = "welcome";

cout<<"The content of first string : " <<first <<"\n";
cout<<"The content of second string : " <<second <<"\n";


// comparing the characters of first string with the characters in second string 
int result = strcmp(first, second);

cout<<"String comparison between " <<first <<" and " <<second <<" : " <<result <<"\n";

// comparing the characters of first string with the characters in second string
result = strcmp(second, third);

cout<<"String comparison between " <<second <<" and " <<third <<" : " <<result;

return 0;
}

Output is -

The content of first string : Welcome
The content of second string : Welcome
String comparison between Welcome and Welcome gives : 0
String comparison between Welcome and welcome gives : -1

On the first call to the strcmp(), it compares the characters in the first char[] array with the characters in the second char[] array and returns 0 i.e. both the string values are the same.
On the second call to the strcmp(), it compares the characters in the second char[] array with the characters in the third char[] array and returns -1 i.e. because there the ASCII value of 'W' in second char [] array is smaller than ASCII value of 'w' in the third char[] array.

Another example of strcmp() function

strcmp()

char[]

The first char[] array i.e. first is initialized with a string value Sky is blue
The second char[] array i.e. second is also initialized with the same value Sky is orange.

// strcmp example 

#include<iostream>
#include<cstring>

using namespace std;

int main()
{
char first[15] = "Sky is blue";
char second[15] = "Sky is orange";

cout<< "The content of first string : " << first << "\n";
cout<< "The content of second string : " << second << "\n";


// comparing the characters of first string with the characters in second string
int result = strcmp(first, second);

cout<< "String comparison between " << first << " and " << second << " : " << result;

return 0;
}

Output is -

The content of first string : Sky is orange
The content of second string : Sky is blue
String comparison between Sky is orange and Sky is blue gives : 1

On the call to the strcmp(), it compares the characters in the first char[] array with the characters in the second char[] array and returns 1 i.e. because when comparing Sky is blue with Sky is orange, the ASCII value of 'o'jj in first char [] array is larger than ASCII value of 'b' in the second char[] array.