What exactly are null pointers? C++ coders should be able to answer this question in a second. So, for those who are in a dilemma regarding this topic, do not worry, because we got you covered. In this article, we will learn about 'nullptr' in C++ with examples.
What is a nullptr in C++?
In C++, the null pointer, often written as “nullptr”, can be defined as a keyword that is used to represent the absence of a memory address. In a program, whenever an object is created, it is called whenever needed. It is mainly used to show that a pointer is temporarily not pointing at any legitimate object or element.
The null ptr is used in numerous situations like dereferencing a pointer to check if it’s valid or not, comparing two or more pointers, as well as initializing pointers themselves. But, keep in mind that dereferencing a null pointer is regarded as undefined behavior and may cause crashes in a program or other issues.
The syntax of null pointer is “nullptr” without any specific characters or additional punctuation. Here is an example:
#include int main() { int* ptr1 = nullptr; // initialize pointer to null pointer int* ptr2 = new int(42); // dynamically allocate an integer and assign its address to ptr2 if (ptr1 == nullptr) { std::cout << "ptr1 is a null pointer!" << std::endl; } else { std::cout << "ptr1 is not a null pointer!" << std::endl; } if (ptr2 == nullptr) { std::cout << "ptr2 is a null pointer!" << std::endl; } else { std::cout << "ptr2 is not a null pointer!" << std::endl; std::cout << "The value pointed to by ptr2 is " << *ptr2 << std::endl; } delete ptr2; // free dynamically allocated memory return 0; }
Output:
ptr1 is a null pointer! ptr2 is not a null pointer! The value pointed to by ptr2 is 42
In the above instance, two pointers, ptr1, and ptr2 have been declared. With nullptr, ptr1 is initialized to a null pointer, and the new operator, ptr2, is given the address of an integer that was allocated dynamically.
Using the == operator, we then determine whether each pointer is a null pointer and print the results to the console. We additionally dereference the pointer in the case of ptr2 to print the value that ptr2 pointed to.
Lastly, we release the dynamically allocated memory referenced by ptr2 using the delete operator. Due to its initialization to nullptr in this example, ptr1 is a null pointer. Because it links to a usable memory address, ptr2 is not a null pointer (the address of the dynamically allocated integer).
Does nullptr == 0 in C++?
We know that the nullptr is a keyword that represents a null pointer constant. On the other hand, 0 is an integer literal with the value zero. We can say that both nullptr and 0 represent null pointers, they are not the same. In general, it is recommended to use nullptr in modern C+.
What is the best way to check nullptr in C++?
The equality operator (==) is the recommended method for detecting a null pointer (nullptr) in C++. Here's an illustration:
int* ptr = nullptr; if (ptr == nullptr) { // Do something if ptr is a null pointer }
With the == operator, we are determining in this example whether ptr is equal to nullptr.
The code contained in the if block will run if ptr is a null pointer. Moreover, it is typically advised to not use the inequality operator,i.e, “!=” to check for null pointers, because doing such a thing could result in unwanted subtle errors if the code is eventually changed to use a non-null pointer constant like NULL or 0 integers in place of the nullptr.
In addition to this, it is also advised to initialize the nullptr using the equality operator, like int* ptr = nullptr;
This prevents undefined behavior when the pointer is dereferenced and it also makes sure that the pointer points to a null address.
Why use null pointers in C++?
The following are some typical C++ use cases for null pointers:
- Initialization of pointers: In C++, a pointer does not always point to an appropriate object or function when it is declared at the very beginning. An uninitialized pointer's value is undefined by default. This is why, a good technique to show that a pointer is now referring to nothing as of now is to initialize it to a null pointer (using nullptr).
- Checking for valid pointers: It is very important to make sure that a pointer is valid before dereferencing it, i.e., accessing the memory location it had been pointing to. It is easy to establish whether it is acceptable to dereference a pointer by checking whether it is a null pointer using nullptr.
- Returning error codes: A null pointer can be returned by functions in C++ as an error code or to indicate that a specific value could not be returned. For instance, if a function is designed to return a pointer to a dynamically allocated object but is unable to do so due to memory allocation issues, it may instead return a null pointer as a failure indication.
Null pointers are often a helpful tool for handling circumstances when pointers may not be leading to legitimate objects or methods. They can be employed to flag faults or unusual circumstances in C++ applications and aid in the prevention of undeclared behavior.
Advantages of nullptr
Following are some of the advantages of null pointers that you should know about:
- Safer programming: With the help of a null pointer, segmentation faults, and undefined behavior can be avoided by representing a pointer that is not now pointing to a valid object or function.
- Easy to understand Code: By using a null pointer, we may make our code plain. We may clearly show that a pointer is now referring to nothing by initializing it to a null pointer using nullptr.
- Portable: Most compilers and platforms support null pointers, a common C++ feature. We may make sure that our code is portable and can be built and executed on a variety of computers by using null pointers.
- Compatible: Null pointers are compatible with null pointer constants in the C style (such as NULL and 0). This implies that old C code that uses these constants and null pointers can communicate with each other in C++.
Also, you should also learn about function pointers in C++
Conclusion
With the introduction of nullptr in C++11, no memory location is specified. And to distinguish between NULL and the genuine null of type pointer, the nullptr C++ conversion operator uses templates. Now hopefully the dilemma is solved, Happy Learning :)
