std::tolower
<cctype>
Converts the given character to lowercase according to the character conversion rules defined by the currently installed C locale.
In the default "C" locale, the following uppercase letters ABCDEFGHIJKLMNOPQRSTUVWXYZ are replaced with respective lowercase letters abcdefghijklmnopqrstuvwxyz.
[edit] Parameters
[edit] Return value
Lowercase version of ch or unmodified ch if no lowercase version is listed in the current C locale.
[edit] Notes
Like all other functions from <cctype>, the behavior of std::tolower is undefined if the argument's value is neither representable as unsigned char nor equal to EOF . To use these functions safely with plain chars (or signed chars), the argument should first be converted to unsigned char:
char my_tolower(char ch) { return static_cast<char>(std::tolower(static_cast<unsigned char>(ch))); }
Similarly, they should not be directly used with standard algorithms when the iterator's value type is char or signed char. Instead, convert the value to unsigned char first:
std::string str_tolower(std::string s) { std::transform (s.begin(), s.end(), s.begin(), // static_cast<int(*)(int)>(std::tolower) // wrong // [](int c){ return std::tolower(c); } // wrong // [](char c){ return std::tolower(c); } // wrong [](unsigned char c){ return std::tolower(c); } // correct ); return s; }
[edit] Example
#include <cctype> #include <clocale> #include <iostream> int main() { unsigned char c = '\xb4'; // the character Ž in ISO-8859-15 // but ́ (acute accent) in ISO-8859-1 std::setlocale (LC_ALL, "en_US.iso88591"); std::cout << std::hex << std::showbase ; std::cout << "in iso8859-1, tolower('0xb4') gives " << std::tolower(c) << '\n'; std::setlocale (LC_ALL, "en_US.iso885915"); std::cout << "in iso8859-15, tolower('0xb4') gives " << std::tolower(c) << '\n'; }
Possible output:
in iso8859-1, tolower('0xb4') gives 0xb4
in iso8859-15, tolower('0xb4') gives 0xb8