How the `auto` keyword is used for return value type inference in C++

The auto keyword in C can be used for return value type inference, allowing the compiler to infer the return value type based on the function body, simplifying function declaration. Specific steps include using auto instead of an explicit return type in function declarations. Based on the implementation of the function body, the compiler will infer the return value type.

Return value type inference of the auto keyword in C

Overview

auto The keyword can not only be used to declare variable types, but can also be used to infer return value types. This technique allows the compiler to infer a function's return type from its body.

Syntax

To use auto for return type inference, simply use auto instead of explicit in the function declaration return type. As shown below:

auto myFunction(int a, int b) {
  return a + b;
}

Practical case

Consider the following function to calculate pi:

double calculatePi(int n) {
  double pi = 0.0;
  for (int i = 1; i <= n; i++) {
    pi += (4.0 / (2.0 * i - 1.0)) * ((i % 2 == 0) ? -1 : 1);
  }
  return pi;
}

Use auto to return the value Type inference can simplify the function declaration as follows:

auto calculatePi(int n) {
  double pi = 0.0;
  for (int i = 1; i <= n; i++) {
    pi += (4.0 / (2.0 * i - 1.0)) * ((i % 2 == 0) ? -1 : 1);
  }
  return pi;
}

At compile time, the compiler will infer that the return value type is double based on the implementation of the function body.

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