Is using an invalid pointer value legal in C?

Question

The following code is undefined behavior in C++ (although it will work okay on almost any widely used implementation):

int* pointer; //uninitialized - likely         


        

Answer 1

It is undefined behavior in C99. The value of pointer is "indeterminate" (6.7.8.10) and an indeterminate value can be a trap value that causes undefinedness when used.