https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81992
--- Comment #4 from Jonny Grant <jg at jguk dot org> --- Hello Jonathan and Daniel Thank you for your replies. The stackoverlflow article suggests using <locale> which provides a std::toupper(). I did change to that, but it still had same issue: A) std::transform(str.begin(), str.end(), str.begin(), std::tolower); B) I changed again, to cast to function pointer, and that did compile: std::transform(str.begin(), str.end(), str.begin(), (int (*)(int))std::tolower); Unsure why it didn't find std::tolower directly as per (A) above. It would have been simpler if C++ never re-used any symbol names that were also present in C.
