C++ SegFault when dereferencing a pointer for cout

Question

I\'m new to C++ and just trying to get a hang of it. It generally seems not too bad, but I stumbled upon this weird/pathological segfaulting behavior:

int ma         


        

Answer 1

int* b points to an unknown memory address because it wasn't initialized. If you initialized it to whatever null pointer value exists for your compiler (0 until C++11, nullptr in C++11 and newer), you'd most certainly get a segfault earlier. The problem lies in the fact that you allocated space for the pointer but not the data it points to. If you instead did this:

int c = 27;
int* b = &c;

cout << "c points to " << c << endl;
printf ("b points to %d\n", *b);
cout << "b points to " << (*b) << endl;

Things would work because int* b refers to a memory location that is accessible by your program (since the memory is actually a part of your program).

If you leave a pointer uninitialized or assign a null value to it, you can't use it until it points to a memory address that you KNOW you can access. For example, using dynamic allocation with the new operator will reserve memory for the data for you:

int* b = new int();
*b = 27;
int c = *b;

//output

delete b;