C++ cstring strcmp() - Compare Two Strings

Introduction

The strcmp() function in C++ is a standard library function that compares two C-style strings (null-terminated). It determines the lexographical order of the strings and is crucial for operations that require string comparison, such as sorting or validating equality. This function is part of the C-string library <cstring>, and it provides an efficient method for evaluating the relationship between two strings.

In this article, you will learn how to use the strcmp() function to compare two strings. This includes understanding its return values, dealing with typical string comparison scenarios, and handling edge cases effectively.

Understanding strcmp()

Basic Usage and Syntax

1. Include the <cstring> header in your C++ program to make use of the strcmp() function.

2. Understand that strcmp() takes two constant character pointers (C-style strings) as arguments and returns an integer.

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   #include <cstring>
   
   int main() {
       const char* str1 = "Hello";
       const char* str2 = "World";
       int result = strcmp(str1, str2);
       return 0;
   }
   

   The strcmp() function compares str1 and str2. The return value stored in result will dictate the lexicographical order of the strings, which is discussed next.

Interpretation of Return Values

1. Analyze the integer returned by strcmp() to determine the relationship between the two strings:

   • A return value of 0 indicates that both strings are equal.
   • A negative return value suggests that the first string (str1) is lexicographically less than the second string (str2).
   • A positive return value implies that the first string (str1) is lexicographically greater than the second string (str2).
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   if (result == 0) {
       std::cout << "Strings are equal." << std::endl;
   } else if (result < 0) {
       std::cout << "First string is less than the second string." << std::endl;
   } else {
       std::cout << "First string is greater than the second string." << std::endl;
   }
   

   By evaluating result, effectively determine the lexicographical relationship between str1 and str2.

Common Use Cases of strcmp()

Comparing Similar Strings

1. Use strcmp() to determine if two strings that look similar are actually the same.

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   const char* str1 = "hello";
   const char* str2 = "hello";
   int result = strcmp(str1, str2);
   

   Since str1 and str2 are identical, strcmp() will return 0.

Case Sensitivity Considerations

1. Recognize that strcmp() is case-sensitive, which affects its comparison outcome.

2. Directly compare two strings with differing cases to see how strcmp() behaves.

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   const char* str1 = "Hello";
   const char* str2 = "hello";
   int result = strcmp(str1, str2);
   

   The comparison will result in a non-zero value, indicating the strings are different due to case sensitivity.

Conclusion

The strcmp() function in C++ is an essential tool for comparing C-style strings. It offers precise lexographical comparisons and can be used to sort arrays of strings or validate string equality. By understanding and using the examples provided, effectively leverage strcmp() in your applications to handle string comparisons efficiently and accurately. Whether comparing file paths, user inputs, or any data derived from strings, strcmp() will provide reliable and consistent results.