Q: Is it safe to assume that the right-hand side of the && and || operators won't be evaluated if the left-hand side determines the outcome?
A: Yes. Idioms like
if(d != 0 && n / d > 0)
{ /* average is greater than 0 */ }
and
if(p == NULL || *p == '\0')
{ /* no string */ }
are quite common in C,
and depend on
this so-called short-circuiting behavior.
In the first example,
in the absence of short-circuiting behavior,
the right-hand side would divide by 0--and perhaps crash--if
d were equal to 0.
In the second example,
the right-hand side would attempt to reference
nonexistent memory--and perhaps crash--if
p were a null pointer.
References:
ISO Sec. 6.3.13, Sec. 6.3.14
H&S Sec. 7.7 pp. 217-8
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