When Should You Use `nullptr` in C ?

When to Use nullptr

In C code, pointers can be initialized to conceptually equivalent values: nullptr, NULL, or 0. While these values all indicate a null pointer, nullptr offers several advantages.

Overloaded Function Invocation

Consider the following overloaded functions:

void f(char const *ptr);
void f(int v);

In the absence of nullptr, the following call would lead to ambiguity:

f(NULL);  //which function will be called?

However, using nullptr clarifies the intended function invocation:

f(nullptr); //first function is called

Template Specialization for nullptr

Additionally, nullptr allows for template specialization specifically for null pointers. Consider the following template:

template<typename T, T *ptr>
struct something{};                     //primary template

The following partial specialization can be defined for nullptr:

template<>
struct something<nullptr_t, nullptr>>{};  //partial specialization for nullptr

This enables creating a dedicated overload for handling nullptr arguments:

template<typename T>
void f(T *ptr);   //function to handle non-nullptr argument

void f(nullptr_t); //an overload to handle nullptr argument!!!

Type Deduction for nullptr

In templates, the type of nullptr is deduced as nullptr_t. This simplifies the code, as seen below:

template<typename T>
void f(T *ptr);   //function to handle non-nullptr argument

void f(nullptr_t); //an overload to handle nullptr argument!!!

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