Description |
 |
Each of the operands must have scalar type. The type of the
left operand need not be related to the type of the right operand.
The result has type int
and has a value of 1 if both of its operands compare unequal to
0, and 0 otherwise. The result is not an lvalue.
The logical AND operator guarantees left-to-right evaluation.
If the first operand compares equal to zero, the second operand
is not evaluated.
This feature is useful for pointer operations involving pointers
that can be NULL. For example, the following statement:
if(p!=NULL && *p=='A') *p='B'; |
The first operand tests to see if pointer p
is NULL. If p
is NULL, an indirect reference could cause a memory access violation.
If p is non-NULL,
the second operand is safe to evaluate. The second expression checks
to see if p points
to the character 'A'.
If the second expression is true, the
&& expression is true and the character that p
points to is changed to 'B'.
Had the pointer been NULL, the if
statement would have failed and the pointer would not be used indirectly
to test for the 'A' character.
