no matching function transform?

http://stackoverflow.com/questions/19876746/stdtolower-and-visual-studio-2013

http://forums.codeguru.com/showthread.php?489969-no-matching-function-transform

std::tolower is overloaded in C++, it's declared in <cctype> as

int tolower(int);

and also in <locale> as

template<CharT> CharT tolower(CharT, const locale&);

so when you say "std::tolower" you get an ambiguous(模糊不清的) reference to an overloaded function.

1. Why ::tolower version is working?

When you include <cctype> the one-argument overload is declared in namespace std and mightalso be declared in the global namespace, depending on the compiler. If you include <ctype.h> then it's guaranteed to be included in the global namespace, and ::tolower will work (although note Dietmar's points about when it's not safe). The two-argument overload from <locale> is never declared in the global namespace, so ::tolower never refers to the two-argument overload.

2. Why std::tolower is not working in std::transform?

See above, it's an overloaded name.