Data allocation to pointers in C

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

Don't rely on it. This depends on an omptimization the compiler does to reduce the size of the binary.

Answer 2

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]).

Answer 3

If you are comparing strings shouldnt you be using strcmp ?

Answer 4

It is not about some "data allocation to pointers". It is about whether each instance of string literal is guaranteed to be a different/distinct array object in C. The answer is no, they are not guaranteed to be distinct. The behavior in this case is implementation-dependent. You can get identical pointers in your example, or you can get different pointers.