How to use void in c++

The void keyword in C is used to specify that a function does not return any value. Its usage includes: defining a function without a return value, declaring a function pointer or reference as a placeholder or default value type inference

Usage of void in C

void is a keyword in C, used to specify that the function has no return value. It is used in the following situations:

1. Define a function without a return value:

<code class="cpp">void print_message() {
  std::cout << "Hello World!" << std::endl;
}</code>

2. Declare a function pointer or reference:

<code class="cpp">void (*callback)(int); // 指向接收int参数并无返回值的函数的指针
void& func_ref = my_function; // 引用到无返回值函数</code>

3. As a placeholder or default value:

In some cases, void can be used as a placeholder or default value. For example:

• In a macro definition, void can indicate that no code is generated when the macro is expanded:

  <code class="cpp">#define MY_MACRO(x) x
  #define EMPTY_MACRO() void</code>

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• In template metaprogramming, void Can indicate that the type or value does not exist:

  <code class="cpp">template<typename T>
  void foo() {
  static_assert(std::is_same<T, void>::value, "T must be void");
  }</code>

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  4. Type inference:

  In C 14 and later, void can be used For type inference, it means that the function returns an untyped expression:

  <code class="cpp">auto result = []() { return 42; }(); // result类型为int</code>

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  Note:

  • void is not a type, so you cannot use void to declare a variable or object.
  • The void function cannot explicitly return any value (including void).
  • The void function can use the return statement to end the execution of the function.

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