Question

char *p = "abc"; 
char *q = "abc"; 

if (p == q) 
printf ("equal"); 
else 
printf ("not equal"); 

Output:
equal

Is it compiler specific, or is it defined somewhere in the standards to be as expected behaviour.

Answer 1

The compiler is permitted to ‘coalesce’ string literals, but is not required to.

From 6.4.5/6 String literals:

It is unspecified whether these arrays are distinct provided their elements have the
appropriate values.

In fact, the compiler could merge the following set of literals:

char* p = "abcdef";
char* q = "def";

such that q might point ‘inside’ the string pointed to by p (ie., q == &p[3]).