Compare strings in C#

Here you will learn which is the best way to check whether the two strings are equal or not in C#.

You can check the equality of strings using two ways:

1. Using == operator
2. Using Equals() method

Let's see different scenarios of comparing string equalities.

Compare Case-Sensitive Strings

Both, == and Equals() method compares the content of strings. So, there is no difference between them when you compare strings case-sensitive and in en culture.

string str1 = "London";
string str2 = "London";
 
str1 == str2; // true
str1.Equals(str2); // true

What happens if a string is null?

string str1 = "London";
string str2 = null;

str1 == str2; // false
str1.Equals(str2); // false
str2.Equals(str1); // NullReferenceException

As you can see above, there is no problem with == operator if a string is null. But, calling the Equals() method on null will throw the NullReferenceException. So, you have to make sure a string is not null before calling the Equals() method.

Now, consider the following example where comparing a string with an object type.

string str1 = "London";
object obj = "London";
 
str1 == obj; // true
str1.Equals( obj); // true
obj.Equals(str1); // true

So, it gives the correct result when comparing a string with an object.

Now, let's see a little complicated scenario.

string str = "London";
StringBuilder sb = new StringBuilder("London");
object obj = sb.ToString();
 
str == obj; // false
str == sb.ToString();// true
str.Equals(obj);// true
obj.Equals(str1); //true

In the above example, str == obj returns false even though the values are the same. Why?

The String type implements == operator overload, which compares the value of two operands. However, after casting StringBuilder to object, it calls different overloads where it compares reference of the two operands. So, str == obj gives the wrong result.

So, if you are comparing strings case-sensitive, then in most cases == and Equals() will behave the same. However, in the scenario like above, == gives the wrong result.

Compare Case-Insensitive Strings

The == operator always compares strings case-sensitive.

string str1 = "LONDON";
string str2 = "london";    

str1 == str2; //false

Use the Equals() method to compare strings case-insensitive using StringComparison parameter.

string str1 = "LONDON";
string str2 = "london";

str1.Equals(str2, StringComparison.CurrentCultureIgnoreCase); // true

Always make sure that string is not null using null-conditional operator ? before calling Equals() method, as shown below.

string str1 = null;
string str2 = "london";

str1?.Equals(str2, StringComparison.CurrentCultureIgnoreCase); // true

== vs Equals

Conclusion

If you are sure that the type of two operands are string and want to compare string case-sensitive, then both will give the right result. However, you don't know the type of operands and want to compare strings case-insensitive or want to compare culture-specific strings then use the Equals() method. Just make sure that a string is not null on which you call the Equals() method.

Learn about string comparison in detail.

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