I'm just wondering if this is a safe practice.
My compiler has no problems with this but I'm guessing that dereferencing a NULL pointer is unsafe.Code:#include <stdio.h> int main(int argc, char ** argv) { int * i_ptr = NULL; fprintf(stdout, "size: %lld\n", sizeof(*i_ptr));//How safe is it to deference a NULL pointer here to get the data size? return 0; }
sizeof is a compile time operation, not run-time.
The actual initialised (or not) value of the pointer doesn't matter.
The only dereferencing going on is the type to arrive at sizeof(int).
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.
So basically the compiler knows how big the pointer's data type is...Originally Posted by Salem
Yes. The sizeof operation returns the size of a type. It is not related to the value of a variable. That's the reason why it works.
FWIW There's an exception for the compile time evaluation. The size of a VLA can only be determined at run time. However, this doesn't apply for your example.
