Null pointer usage

The above program shows some unpredictable results and causes the program to crash. Therefore, we can say that keeping an uninitialized pointer in a program can cause serious harm to the computer.

We can avoid the above situation by using the Null pointer. A null pointer is a pointer pointing to the 0 th memory location, which is a reserved memory and cannot be dereferenced. After creating a pointer variable, we add the condition in which we check whether the value of a pointer is null or not.

In the above code, we use the library function, i. As we know, that malloc function allocates the memory; if malloc function is not able to allocate the memory, then it returns the NULL pointer. Therefore, it is necessary to add the condition which will check whether the value of a pointer is null or not, if the value of a pointer is not null means that the memory is allocated.

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Command Line Arguments. Operator in C. Next Topic C dereference pointer. So, from a compiler perspective, there is nothing wrong. Null belongs to String type and Java will not even print a warning. Actually, you can compile even the next code:.

NullPointerException is a Runtime exception that is thrown when Java tries to call any method on a real object but in runtime this object references to the Null Reference. More details about exceptions and their nature you can find in this article. Developers are humans and use to make mistakes to forget and to haste. As a consequence, they miss to:.

There is no cure for human nature and there is nothing to do with it. What are the practical ways to avoid NPE? Let's review an example in the next chapter and try to fix it.

In our example, we have a User object with an Address field. Potentially, both of them might be null. Let's see how we can avoid NullPointerException. Can we improve this solution? Yes, we can use Optional. Using map function we can write equivalent similar to the previous statement:. Does optional provide benefits compared to simple null check? Yes, it does. Optional reinsures us that data we use in ifPresent lambda is not null. But, what if the user or address is null?

Then, ifPresent will be silently ignored. And, even if we forget to use Optional features, the idea will highlight. The optional feature was released in Java 1. There are a couple of reasons:. The void is one of the data types in C. Whereas, NULL is the value which is assigned to the pointer. The data type of the pointer is nothing but the type of data stored at the memory location where the pointer is pointed.

When you are not sure about the type of data that is going to store at a particular memory location, you need to create the void pointer. We know that in Linked List, we point one node to its successor node using a pointer. As there is no successor node to the last node, you need to assign a NULL value to the link of the last node. As shown in above image. I have described it in detail. The understanding of the NULL pointer is a concept. Like C programming, you can see the same use cases of NULL pointers in many other programming languages.

Many of the programming languages use the NULL pointer concept. It is not necessary to have the same name for a NULL pointer, but the concept is almost the same in all the programming languages. You will find NULL pointer and macro very useful.

If you have any question, feel free to ask in a comment. Great Post. Agree with Mathew. From C11 standard clause 6. If a null pointer constant is converted to a pointer type, the resulting pointer, called a null pointer, is guaranteed to compare unequal to a pointer to any object or function.

This is also called the C11 standard. But C standard is saying that 0 is also a null pointer constant. It means that the following is also perfectly legal as per standard. This is one of the reasons why the usage of NULL is preferred because it makes it explicit in code that programmer is using null pointer, not integer 0.

This statement is also from C11 clause 7. It means that internal representation of the null pointer could be non-zero bit pattern to convey NULL pointer. Having said so, typically NULL is represented as all bits set to 0 only. Well, usage of sizeof NULL is allowed but the exact size would depend on platform.