With "-fno-exceptions", what happens with "new T"?

Question

I was wondering, will new T still throw bad_alloc if I compile my program using the -fno-exceptions option to disable exception handling?

Or will the compiler (GCC and clang support that option) implicitly transform the use of new T to new (nothrow) T?

Answer 1

The way I understand it, operator new is defined by libstdc++. If you now compile your own code with -fno-exceptions, you cannot catch any exceptions, but you will still be linking against the normal version of libstdc++, which does throw an exception.

So yes, new T will throw an exception, even with -fno-exception.

However, if you compiled libstdc++ with -fno-exception as well, things become different. Now, new T cannot throw an exception but, if I read the libstdc++ manual right it will call abort() instead.

It seems that, if you want your new T to return NULL on failure, the only way is to explicitely specify nothrow...

Answer 2

I can't give a definitive answer to all the perks around -fno-exceptions, just the observations on a 32 bit linux machine, gcc 4.5.1 - bad_alloc is thrown with and without -fno-exceptions

[21:38:35 1 ~/tmp] $ cat bad_alloc.cpp  int main() {     char* c = new char[4000000000U]; } [21:38:58 1 ~/tmp] $ g++ bad_alloc.cpp [21:39:06 1 ~/tmp] $ ./a.out terminate called after throwing an instance of 'std::bad_alloc'   what():  std::bad_alloc Aborted [21:39:07 1 ~/tmp] $ g++ -fno-exceptions bad_alloc.cpp [21:39:16 1 ~/tmp] $ ./a.out terminate called after throwing an instance of 'std::bad_alloc'   what():  std::bad_alloc Aborted