The following code terminates abruptly when the printf is uncommented, but works fine with printf commented out. Isn't it supposed to terminate as soon as the control reaches line no.7 (irrespective of printf commented or otherwise)??
Code:#include<stdio.h> int main() { int *p, i; p = (int*)0x1234; i = *p; //printf("%d",i); }
No, it is supposed to print "hello world!".
In other words, once there is undefined behaviour, it is unreasonable to expect the program to terminate at the point where undefined behaviour is introduced. The program can continue running "perfectly fine".
Look up a C++ Reference and learn How To Ask Questions The Smart WayOriginally Posted by Bjarne Stroustrup (2000-10-14)
So does that mean that we can never directly access any memory outside of our address space.
Why do you ask? Anyway, I think the answer is: it depends (e.g., an operating system might allow it, or there might not be an operating system).
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I suppose you're trying to tell me that its not possible. But what if the page we are trying to access has read only attributes, can we not read it if we need to?
Hmm... are you trying to do some kind of interprocess communication? There are ways to legitimately share memory, for example.
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May be I should wait until I get into the intricasies of operating systems but for now should I assume that we can't access (read) anything outside of our address space?
Yes, if you don't need to do otherwise, assuming that is fine.
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It's more likely that in the absence of the side effect (printing it), the compiler optimises the program down to nothing.
Certainly gcc -O2 eliminates what would otherwise be a disaster.
If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
If at first you don't succeed, try writing your phone number on the exam paper.
