https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80684
Eric Gallager <egallager at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- Status|UNCONFIRMED |NEW Last reconfirmed| |2017-08-18 CC| |egallager at gcc dot gnu.org Ever confirmed|0 |1 --- Comment #1 from Eric Gallager <egallager at gcc dot gnu.org> --- For me the fix-it is just: $ /usr/local/bin/g++ -S -Wall -Wextra -pedantic 80684.cc 80684.cc:1:15: error: variable or field ‘f’ declared void void f (string); ^ 80684.cc:1:9: error: ‘string’ was not declared in this scope void f (string); ^~~~~~ 80684.cc:1:9: note: suggested alternative: ‘__strong’ void f (string); ^~~~~~ __strong $ When I include the header, the message is: $ /usr/local/bin/g++ -S -Wall -Wextra -pedantic 80684.cc 80684.cc:3:15: error: variable or field ‘f’ declared void void f (string); ^ 80684.cc:3:9: error: ‘string’ was not declared in this scope void f (string); ^~~~~~ 80684.cc:3:9: note: suggested alternative: In file included from /usr/local/include/c++/8.0.0/string:39:0, from 80684.cc:1: /usr/local/include/c++/8.0.0/bits/stringfwd.h:74:33: note: ‘std::__cxx11::string’ typedef basic_string<char> string; ^~~~~~ $ It seems like in this second case where <string> is already included, the ideal fix-it would be to suggest inserting the 'std::' prefix before 'string', or adding a "using namespace std;" directive earlier in the file. Thus, confirming.