c++ - Are all functions "noexcept" if exceptions are disabled? -

if turn off exceptions compiling -fno-exceptions functions considered noexcept example std::move_if_noexcept or still have declare functions noexcept reason?

the -fno-exceptions prevent throwing exceptions, can not prevent exceptions being thrown libraries.

for example, next example terminate because of not caught exception :

#include <vector>  int main() {     std::vector<int> v{1,2,3,4,5,6};      return v.at(55); } 

but next example not compile, because of -fno-exceptions option :

int main() {     throw 22; } 

it fails :

g++   -std=c++11 -g  -wall -wextra -fno-exceptions ./garbage.cpp  ./garbage.cpp: in function ‘int main()’: ./garbage.cpp:4:8: error: exception handling disabled, use -fexceptions enable   throw 22; 

from this article, doing without chapter :

user code uses c++ keywords throw, try, , catch produce errors if user code has included libstdc++ headers , using constructs basic_iostream.

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on other hand, noexcept marks method method doesn't throw exceptions. thrown exception call std::terminate (see [except.terminate]/2 in c++ standard).

next example :

struct {     void foo() noexcept     {         throw 33;     } };  int main() {     a;     try     {         a.foo();     }     catch(...)     {     } } 

terminates :

terminate called after throwing instance of 'int' aborted (core dumped) 

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to conclude : behavior quite different when use -fno-exceptions , when mark function noexcept.

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although compile whole project -fno-exceptions(for other reasons) still have declare move constructors move assigment operators noexcept enable move semantic std::move_if_noexcept?

when use option, functions not automatically marked noexcept. have manually. compiler not allowed such modifications.

if such modification allowed, this example produce different outputs.