Differences between C++ string == and compare()

In C++, the ‘==’ operator and the `compare()` member function of the `std::string` class are both used to compare strings, but they have different characteristics and behaviors. Here are the main differences between the two:

1. Syntax

Using ‘==’ Operator

std::string str1 = "hello";
std::string str2 = "world";
if (str1 == str2) {
    // strings are equal
}

Using ‘compare'() Method:

std::string str1 = "hello";
std::string str2 = "world";
if (str1.compare(str2) == 0) {
    // strings are equal
}

2. Return Type and Values

 

‘==’ Operator

Returns a boolean value ( ‘true’ or ‘false’ ).

Evaluates to ‘true’ if the two strings are equal, and ‘false’ otherwise.

 

‘Compare()’ Method:

Returns an integer value.

Returns ‘0’ if the strings are equal, a negative value if the calling string is less than the argument string, and a positive value if the calling string is greater than the argument string (lexicographically).

 

3. Use cases

 

‘==’ Operator:

Simple and straightforward for checking equality. It is commonly used when you only need to check whether two strings are equal.

‘compare’ Method:

More versatile as it provides more information about the relationship between the two strings (i.e., whether one is less than or greater than the other).

Useful when you need to implement custom sorting or ordering based on string comparison.

 

4. Performance

 

Both methods typically have similar performance characteristics for basic comparison, but the compare() method may have slight overhead due to additional return values. However, in most practical cases, this difference is negligible and won’t significantly affect performance.

 

5. case Sensitivity

 

Both ‘==’ and ‘compare’ are case-sensitive by default. If you need case-insensitive comparisons, you’ll have to implement that logic manually or use additional libraries.

 

6. Compatibility with other Types

 

The ‘==’ operator can be used with ‘std::string and C-style strings (const char*), while compare()  is specifically a member function of std::string .

Example Usage

Here’s an example that demonstrates both methods:

#include <iostream>
#include <string>

int main() {
    std::string str1 = "apple";
    std::string str2 = "banana";

    // Using ==
    if (str1 == str2) {
        std::cout << "Strings are equal using ==\n";
    } else {
        std::cout << "Strings are not equal using ==\n";
    }

    // Using compare()
    int result = str1.compare(str2);
    if (result == 0) {
        std::cout << "Strings are equal using compare()\n";
    } else if (result < 0) {
        std::cout << "str1 is less than str2 using compare()\n";
    } else {
        std::cout << "str1 is greater than str2 using compare()\n";
    }

    return 0;
}

 

Summary

In summary, use the ‘==’operator for simple equality checks and the ‘compare()’method when you need more detailed comparison results. Both methods are part of the C++ ‘std::string’ class and serve their purposes depending on the context of the comparison.