Question

How to perform case-insensitive two strings comparison in C++

Answer 1

#include <iostream>
#include <cctype>
#include <string>

bool equalsIgnoreCase(const std::string& str1, const std::string& str2) {
    if (str1.size() != str2.size()) {
        return false;
    }
    
    for (size_t i = 0; i < str1.size(); ++i) {
        if (tolower(str1[i]) != tolower(str2[i])) {
            return false;
        }
    }
    
    return true;
}

int main() {
    std::string str1 = "profession: c++ programmer";
    std::string str2 = "Profession: C++ PROGRAMMER";

    bool equals = equalsIgnoreCase(str1, str2);

    std::cout << (equals ? "true" : "false") << std::endl;
}


  
/*
run:
  
true
  
*/

 

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Answer 2

#include <algorithm>
#include <iostream>
#include <string>

bool equalsIgnoreCase(const std::string& str1, const std::string& str2) {
    std::string str1Lower = str1;
    std::string str2Lower = str2;
    
    std::transform(str1Lower.begin(), str1Lower.end(), str1Lower.begin(), ::tolower);
    std::transform(str2Lower.begin(), str2Lower.end(), str2Lower.begin(), ::tolower);
    
    return str1Lower == str2Lower;
}

int main() {
    std::string str1 = "profession: c++ programmer";
    std::string str2 = "Profession: C++ PROGRAMMER";

    bool equals = equalsIgnoreCase(str1, str2);

    std::cout << (equals ? "true" : "false") << std::endl;
}


  
/*
run:
  
true
  
*/

 

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