strict-aliasing

When I compile this sample code using g++, I get this warning: warning: dereferencing type-punned pointer will break strict-aliasing rules [-Wstrict-aliasing] The code: #include <iostream> int main() { alignas(int) char data[sizeof(int)]; int *myInt = new (data) int; *myInt = 34; std::cout << *reinterpret_cast<int*>(data); } In this case, doesn't data alias an int, and therefore casting it back to an int would not violate strict aliasing rules? Or am I missing something here? Edit: Strange, when I define data like this: alignas(int) char* data = new char[sizeof(int)]; The compiler warning goes

Question about type punning: why does this code break strict aliasing rules: int main() { int a = 1; short j; printf("%i\n", j = *((short*)&a)); return 0; } and this is not: int main() { int a = 1; short j; int *p; p=&a; printf("%i\n", j = *((short*)p)); return 0; } Build by gcc -fstrict-aliasing . Thank you! They both violate the strict aliasing rule , I am going to quote my answer here which says ( emphasis mine going forward ): code violates the strict aliasing rules which makes it illegal to access an object through a pointer of a different type , although access through a char * is

I use a code where I cast an enum* to int*. Something like this: enum foo { ... } ... foo foobar; int *pi = reinterpret_cast<int*>(&foobar); When compiling the code (g++ 4.1.2), I get the following warning message: dereferencing type-punned pointer will break strict-aliasing rules I googled this message, and found that it happens only when strict aliasing optimization is on. I have the following questions: If I leave the code with this warning, will it generate potentially wrong code? Is there any way to work around this problem? If there isn't, is it possible to turn off strict aliasing from