Difference between dereferencing NULL pointer and uninitialised pointer

Question

On code blocks(C++)

#include
using namespace std;
int main(){
    int *p;
    cout<<*p;
}

produces garbage value

Answer 1

Your expectation of a runtime error is flawed.

Dereferencing an uninitialised/invalid pointer with arbitrary value can do anything at all.

That means the potential symptoms range from:

• nothing happens
• something happens
• a runtime error happens
• your source code is spontaneously edited to use proper standard headers instead of misguidedly hacking in implementation "bits"
• your attitude in the comments section is magically improved
• your cat is murdered
• your cat is not murdered
• your cat is murdered and not murdered
• your cat murders itself
• a black hole opens inside your cat
• a cat opens up inside a black hole

and so on.

This is true for dereferencing NULL, too, but modern commodity hardware tends to treat NULL dereferences specially, usually guaranteeing a segmentation fault to aid in diagnostics. Obviously, a CPU cannot do that for arbitrary pointer values, because they may be valid as far as it knows!