Summary of the usage of CompareTo in C#

In C#,CompareToMethods are usually used to compare the order of the current object with another object. This method is widely used to implementIComparable<T>orIComparer<T>In the interface class so that objects can be sorted or compared.

1. Implement IComparable<T>

If there is a class that needs to be implementedIComparable<T>Interface, need to provide aCompareToMethods to define natural sorting rules between class instances.CompareToThe method returns a negative number to indicate that the current object is smaller than the parameter object, zero means that the two are equal, and positive number to indicate that the current object is larger than the parameter object.

For example, for a class containing a namePerson, can be implemented like this:

public class Person : IComparable<Person>
{
    public string Name { get; set; }

    public int CompareTo(Person other)
    {
        if (other == null) return 1;

        // Compare the names of two Person instances        return ();
    }
}

CompareToMethod is used to compare the current instance with another instance. For strings,CompareToReturns an integer whose value indicates the relationship between the current object and the specified object.

• If the return value is 0, it means that the current string is equal to the compared string.
• If the return value is less than 0, it means that the current string is in alphabetical order before the comparison string.
• If the return value is greater than 0, it means that the current string is following the comparison string in alphabetical order.

Therefore, expressionm_szAPRCode.CompareTo("03002") != 0The checked ism_szAPRCodewhetherNot equal to "03002". ifm_szAPRCodeand"03002"Equal, thenCompareToThe result will be 0 and the entire expression will become0 != 0, this will returnfalse; On the contrary, if the two are not equal,CompareToThe result will not be 0, and the entire expression will returntrue。

If you want to check whether it is equal, you can use it directly==Operators to compare strings, for example:

if (m_Code == "03003")
{
    // Execute when m_Code equals "03003"}

In addition, useCompareToWhen you need to pay attention to string sorting rules (such as culturally relevant sorting), as well as case sensitivity. Normally, use directly==Comparing strings is an easier and less error-prone way.

2. Use CompareTo for comparison

Once thereCompareToMethod, you can use it to perform comparison operations.

For example, in a LINQ query or array sort:

List<Person> people = new List<Person>
{
    new Person { Name = "Alice" },
    new Person { Name = "Bob" },
    new Person { Name = "Charlie" }
};

// Sort Person lists using CompareTo();

// Or use LINQvar sortedPeople = (p => p);

3. CompareTo in the basic type

Many built-in basic types such asint, string, DateTimeAll have been realizedIComparableInterface, and providesCompareTomethod.

For example:

string str1 = "apple";
string str2 = "banana";

int result = (str2); // Return negative number，because "apple" < "banana"

Anyway,CompareTois a very useful method to determine the relative order between objects. It is not only important in custom classes, but also essential in handling built-in types and sorting algorithms.

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