如何将 std: : string 转换为小写？

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 use with a std::string would require iterating over each character.

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

转载于:https://stackoverflow.com/questions/313970/how-to-convert-stdstring-to-lower-case

Answer 1

From this:

#include <algorithm>
#include <string> 

std::string data = "Abc"; 
std::transform(data.begin(), data.end(), data.begin(), ::tolower);

You're really not going to get away with 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 non-portable alternative that I don't recommend you use:

char easytolower(char in) {
  if(in <= 'Z' && in >= 'A')
    return in - ('Z' - 'z');
  return in;
}

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

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.