strlen not checking for NULL

Question

Why is strlen() not checking for NULL?

if I do strlen(NULL), the program segmentation faults.

Trying to understand the rationale be

Answer 1

Three significant reasons:

• The standard library and the C language are designed assuming that the programmer knows what he is doing, so a null pointer isn't treated as an edge case, but rather as a programmer's mistake that results in undefined behaviour;

• It incurs runtime overhead - calling strlen thousands of times and always doing str != NULL is not reasonable unless the programmer is treated as a sissy;

• It adds up to the code size - it could only be a few instructions, but if you adopt this principle and do it everywhere it can inflate your code significantly.