c++ - 'ptr_fun(isalnum)' 不会在 g++ 中编译？

Answer 1

You should give it a little help in deducing the template types:

std::not1(std::ptr_fun<int, int>(isalnum)))

or by fully qualifying it:

std::not1(std::ptr_fun(::isalnum)))

it seems that gcc and clang have multiple overload resolution candidates due to the locale functions.