$ clang++ -std=gnu++11 -g std_string_custom_new1.cpp 
std_string_custom_new1.cpp:21:7: error: 'basic_string' is not a class, namespace, or enumeration
void *basic_string::operator new(size_t size)
      ^
/usr/bin/../lib/gcc/x86_64-linux-gnu/10/../../../../include/c++/10/bits/basic_string.h:77:11: note: 'basic_string' declared here
    class basic_string
          ^
1 error generated.