Question

I want to convert a std::string to lowercase. I am aware of the function tolower(). However, in the past I have had issues with this function and it is hardly ideal anyway as using it with a std::string would require iterating over each character.

Is there an alternative which works 100% of the time?

Answer 1

Adapted from Not So Frequently Asked Questions:

#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.