How to convert an instance of std::string to lower case

#include <algorithm>

#include <cctype>

#include <string>



std::string data = "Abc";

std::transform(data.begin(), data.end(), data.begin(),

    [](unsigned char c){ return std::tolower(c); });

You're really not going to get away without iterating through each character. There's no way to know whether the character is lowercase or uppercase otherwise.

If you really hate tolower(), here's a specialized ASCII-only alternative that I don't recommend you use:

char asciitolower(char in) {

    if (in <= 'Z' && in >= 'A')

        return in - ('Z' - 'z');

    return in;

}

std::transform(data.begin(), data.end(), data.begin(), asciitolower);
Be aware that tolower() can only do a per-single-byte-character substitution, which is ill-fitting for many scripts, especially if using a multi-byte-encoding like UTF-8.

4 years ago

Boost provides an algorithm of this

#include <boost/algorithm/string.hpp>



std::string str = "HELLO, WORLD!";

boost::algorithm::to_lower(str); // modifies str

And for non-in-place

#include <boost/algorithm/string.hpp>



const std::string str = "HELLO, WORLD!";

const std::string lower_str = boost::algorithm::to_lower_copy(str);

4 years ago