How To Compare Two Strings In Dev C++

10.01.2021

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Mar 15, 2018 What strcmp returns: 0: If both strings are exactly equal. 0: If ASCII value of first mismatch character in secondStr is less than corresponding character in firstStr. Compare if two strings are equal using strcmp Suppose we have two strings i.e. String is considered a compound data type, but it is the exception to the rule, so you can use to compare two strings; however, there are times when you want to compare two strings.

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You compare strings to answer one of two questions: 'Are these two stringsequal?' or 'In what order should these strings be placed when sorting them?'

Those two questions are complicated by factors that affect string comparisons:

You can choose an ordinal or linguistic comparison.
You can choose if case matters.
You can choose culture-specific comparisons.
Linguistic comparisons are culture and platform-dependent.

Note

The C# examples in this article run in the Try.NET inline code runner and playground. Select the Run button to run an example in an interactive window. Once you execute the code, you can modify it and run the modified code by selecting Run again. The modified code either runs in the interactive window or, if compilation fails, the interactive window displays all C# compiler error messages.

When you compare strings, you define an order among them. Comparisons areused to sort a sequence of strings. Once the sequence is in a known order,it is easier to search, both for software and for humans. Other comparisonsmay check if strings are the same. These sameness checks are similar toequality, but some differences, such as case differences, may be ignored.

Default ordinal comparisons

By default, the most common operations:

String.Equality and String.Inequality, that is, equality operators and !=, respectively

perform a case-sensitive ordinal comparison and, if necessary, use the current culture. The following example demonstrates that:

The default ordinal comparison doesn't take linguistic rules into account when comparing strings. It compares the binary value of each Char object in two strings. As a result, the default ordinal comparison is also case-sensitive.

Note that the test for equality with String.Equals and the and != operators differs from string comparison using the String.CompareTo and Compare(String, String) methods. While the tests for equality perform a case-sensitive ordinal comparison, the comparison methods perform a case-sensitive, culture-sensitive comparison using the current culture. Because the default comparison methods often perform different types of comparisons, we recommend that you always make the intent of your code clear by calling an overload that explicitly specifies the type of comparison to perform.

Case-insensitive ordinal comparisons

The String.Equals(String, StringComparison) methodenables you to specify a StringComparison value ofStringComparison.OrdinalIgnoreCasefor a case-insensitive ordinal comparison. There is also a staticString.Compare(String, String, StringComparison) method that performs a case-insensitive ordinal comparison if you specify a value of StringComparison.OrdinalIgnoreCase for the StringComparison argument. These are shown in the following code:

When performing a case-insensitive ordinal comparison, these methods use the casing conventions of the invariant culture.

Linguistic comparisons

Strings can also be ordered using linguistic rules for the current culture.This is sometimes referred to as 'word sort order.' When you perform alinguistic comparison, some nonalphanumeric Unicode characters might havespecial weights assigned. For example, the hyphen '-' may have a very smallweight assigned to it so that 'co-op' and 'coop' appear next to each otherin sort order. In addition, some Unicode characters may be equivalent to asequence of Char instances. The following example uses the phrase'They dance in the street.' in German with the 'ss' (U+0073 U+0073) in one string and 'ß' (U+00DF) in another. Linguistically(in Windows), 'ss' is equal to the German Esszet: 'ß' character in both the 'en-US'and 'de-DE' cultures.

This sample demonstrates the operating system-dependent nature of linguisticcomparisons. The host for the interactive window is a Linux host. Thelinguistic and ordinal comparisons produce the same results. If youran this same sample on a Windows host, you would see the following output:

On Windows, the sort order of 'cop', 'coop', and 'co-op' change when youchange from a linguistic comparison to an ordinal comparison. The twoGerman sentences also compare differently using the different comparison types.

Comparisons using specific cultures

This sample stores CultureInfo objects for the en-US and de-DE cultures.The comparisons are performed using a CultureInfo object to ensure a culture-specific comparison.

The culture used affects linguistic comparisons. The following exampleshows the results of comparing the two German sentences using the 'en-US' cultureand the 'de-DE' culture:

Culture-sensitive comparisons are typically used to compare and sort strings input by users with other strings input by users. The characters and sorting conventions of these strings might vary depending on the locale of the user's computer. Even strings that contain identical characters might sort differently depending on the culture of the current thread. In addition, try this sample code locally on a Windows machine, and you will the following results:

Linguistic comparisons are dependent on the current culture, and are OS dependent. You must take that into account when you work with string comparisons.

Linguistic sorting and searching strings in arrays

The following examples show how to sort and search for strings in an array using a linguistic comparison dependent on the current culture. You use the static Array methods that take a System.StringComparer parameter.

This example shows how to sort an array of strings using the current culture:

Once the array is sorted, you can search for entries using a binary search. A binary search starts in the middle of the collection to determine which half of the collection would contain the sought string. Each subsequent comparison subdivides the remaining part of the collection in half. The array is sorted using the StringComparer.CurrentCulture. The local function ShowWhere displays information about where the string was found. If the string was not found, the returned value indicates where it would be if it were found.

Ordinal sorting and searching in collections

The following code uses the System.Collections.Generic.List<T> collection class to store strings. The strings are sorted using the List<T>.Sort method. This method needs a delegate that compares and orders two strings. The String.CompareTo method provides that comparison function. Run the sample and observe the order. This sort operation uses an ordinal case sensitive sort. You would use the static String.Compare methods to specify different comparison rules.

Once sorted, the list of strings can be searched using a binary search. The following sample shows how to search the sorted listed using the same comparison function. The local function ShowWhere shows where the sought text is or would be:

Always make sure to use the same type of comparison for sorting and searching. Using different comparison types for sorting and searching produces unexpected results.

Collection classes such as System.Collections.Hashtable, System.Collections.Generic.Dictionary<TKey,TValue>, and System.Collections.Generic.List<T> have constructors that take a System.StringComparer parameter when the type of the elements or keys is string. In general, you should use these constructors whenever possible, and specify either StringComparer.Ordinal or StringComparer.OrdinalIgnoreCase.

Reference equality and string interning

None of the samples have used ReferenceEquals. This method determines if two stringsare the same object. This can lead to inconsistent results in string comparisons. The following example demonstrates the string interning feature of C#. When a program declares two or more identical string variables, the compiler stores them all in the same location. By calling the ReferenceEquals method, you can see that the two strings actually refer to the same object in memory. Use the String.Copy method to avoid interning. After the copy has been made, the two strings have different storage locations, even though they have the same value. Run the following sample to show that strings a and b are interned meaning they share the same storage. The strings a and c are not.

Note

When you test for equality of strings, you should use the methods that explicitly specify what kind of comparison you intend to perform. Your code is much more maintainable and readable. Use the overloads of the methods of the System.String and System.Array classes that take a StringComparison enumeration parameter. You specify which type of comparison to perform. Avoid using the and != operators when you test for equality. The String.CompareTo instance methods always perform an ordinal case-sensitive comparison. They are primarily suited for ordering strings alphabetically.

You can intern a string or retrieve a reference to an existing interned string by calling the String.Intern method. To determine whether a string is interned, call the String.IsInterned method. Dms classic analogue waves serum download.

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First of all, for any type (string or other), the statement 'if ( a = b )' does not check whether a is equal to b, it assigns the value of b to a, and returns the final value a (which is also the value of b). The single = sign is an assignment operator, not a comparison operator. The comparison for equality is , i.e. double equal sign.

Second, the strings that you are using are so-called C-strings (kept for legacy support of C code in C++). The proper string to use is the class 'std::string' (in the '#include <string>' header. Using these, your code will work (with the double equal sign instead of single equal sign for comparisons).

Third, if you have to use 'char *', i.e. C-strings, then there is no equality operator for it, so 'a 'yes' will not work. The proper function to compare two C-strings is strcmp(), which will return 0 if they are equal. Thus: