如何将std :: string转换为小写？

问题描述

我想将 std :: string 转换为小写。我知道函数 tolower（），但是在过去我已经有这个函数的问题，它几乎不理想，因为使用一个字符串将需要迭代每个

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 string would require iterating over each character.

有100％的时间可以使用吗？

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

推荐答案

从：

#include <algorithm>
#include <string>

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

你真的不会离开不迭代每个字符。无法知道字符是小写还是大写。

You're really not going to get away with not iterating through each character. There's no way to know whether the character is lowercase or uppercase otherwise.

如果你真的讨厌tolower（），这里是一个不可移植的替代，我不推荐你使用：

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);

请注意 :: tolower（）只能进行单字节字符替换，这对于许多脚本来说是不合适的，尤其是在使用UTF-8等多字节编码时。

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.

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