Nested Functions In C

Nested Functions In C

In C programming, we can talk about something called “nested functions.” It’s like having a smaller function inside a bigger one. However, in C, these nested functions work a bit differently than in some other languages. They can’t do everything you might expect, and they have some rules to follow. This article will explain what nested functions in C are all about and how they work.

Nested Function And Lexical Scoping

1. Nested Function: In programming, a nested function refers to a function defined inside another function. In some programming languages, like Python or JavaScript, nested functions can access variables from their containing (parent) function. However, in C, true nested functions are not supported. You can declare a function inside another function, but it won’t have access to the local variables of the containing function.
2. Lexical Scoping: Lexical scoping, also known as static scoping, is a way to determine the scope (visibility) of variables in a program. In lexical scoping, the scope of a variable is determined by its location in the source code, and it can access variables from its containing function. While C does have lexical scoping for variables, it doesn’t extend this feature to nested functions.

In C, you can declare a function inside another function, but this is not the same as true nested functions with lexical scoping. The inner function in C can only access global variables from the containing module, not the local variables of the containing function. This limitation is due to how C handles variable scope.

Example 1: To illustrate the Nested Function in C

// C program to illustrate the 
// concept of Nested function. 
#include <stdio.h> 
int main(void) 
{ 
    printf("Main"); 
    int fun() 
    { 
        printf("fun"); 
  
        // defining view() function inside fun() function. 
        int view() 
        { 
            printf("view"); 
        } 
        return 1; 
    } 
    view(); 
} 

Output

Compile time error: undefined reference to `view'

Example 2: Nested Function with the help of GCC extension

In GCC (GNU C Compiler), there is an extension that allows you to declare nested functions. However, to use this extension, you need to start the declarations of these nested functions with the “auto” keyword as a prefix. This extension enables you to define functions inside other functions, which is not a standard feature in C but can be useful in certain programming scenarios.

// C program of nested function 
// with the help of gcc extension 
#include <stdio.h> 
int main(void) 
{ 
    auto int view(); // declare function with auto keyword 
    view(); // calling function 
    printf("Main\n"); 
  
    int view() 
    { 
        printf("View\n"); 
        return 1; 
    } 
  
    printf("Skillvertex"); 
    return 0; 
} 

Output

view
Main
Skillvertex

FAQ- Nested functions in C