为什么在编译过程中会发生以下错误

Question

As part of my program, I used following code:

///////////////
98:::printf("%d",abc->stv)
//////////////
100::if(abc)
//////////////

(the following error was produced)

Possible null pointer dereference: abc - otherwise it is redundant to check if abc is null at line 100

Answer 1

if (abc) tests whether abc is a null pointer or not.

The compiler is warning you that you've already assumed that abc is not a null pointer (by dereferencing it on line 98), which means either

• the if (abc) test is redundant (because it will never be true) or
• the dereferencing of abc on line 98 is potentially incorrect because abc might in fact be null.

Answer 2

If you test for abc it means to the compiler it might be null. Therefore dereferencing the pointer like in abc->stv is a possible error. A solution is to enclose the printf code inside the if block:

if(abc)
{
    printf("%d",abc->stv)
    ...
}