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std::tolower(3) 	       C++ Standard Libary		 std::tolower(3)

NAME
     std::tolower - std::tolower

Synopsis
	Defined in header <cctype>
	int tolower( int ch );

	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  let-
     ters
	abcdefghijklmnopqrstuvwxyz.

Parameters
	ch  - character to be converted. If the value of ch is not representable
     as unsigned
	     char and does not equal EOF, the behavior is undefined

Return value
	Lowercase version of ch or unmodified ch  if  no  lowercase  version  is
     listed in the
	current C locale.

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 argu-
     ment 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); } //  cor-
     rect
			);
	  return s;
      }

Example
     // Run this code

      #include <cctype>
      #include <clocale>
      #include <iostream>

      int main()
      {
	  unsigned char c = '\xb4'; // the character A1/2 in ISO-8859-15
				    // but A' (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

See also
	toupper 	     converts a character to uppercase
			     (function)
			     converts  a  character to lowercase using the ctype
     facet of a
	tolower(std::locale) locale
			     (function template)
	towlower	     converts a wide character to lowercase
			     (function)
	C documentation for
	tolower

http://cppreference.com 	   2024.06.10			 std::tolower(3)
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