How to print “GeeksforGeeks” with empty main() in C, C++ and Java?

3.2

Write a program that prints “GeeksforGeeks” with empty main() function. You are not allowed to write anything in main().

C language

  1. One way of doing this is to apply GCC constructor attribute to a function so that it executes before main() (See this for details).
    #include <stdio.h>
    
    /* Apply the constructor attribute to myStartupFun() 
       so that it is executed before main() */
    void myStartupFun(void) __attribute__((constructor));
    
    /* implementation of myStartupFun */
    void myStartupFun(void)
    {
        printf("GeeksforGeeks");
    }
    
    int main()
    {
    }
    

    Output:

    GeeksforGeeks
  2. In linux, just override the default definition of _start() function so that it would work as a custom startup code. See this article to understand more.
    #include <stdio.h>
    #include <stdlib.h>
    
    int main(void)
    {
    }
    
    // _start() function
    void _start(void)
    {
        printf("GeeeksforGeeks");
    
        // Call main() function
        int var = main();
        exit(var);
    }
    

    Now compile this by following command

    gcc -nostartfiles -o file file.c

    Output:

    GeeksforGeeks

C++ language

  1. The idea is to create a class, have a cout statement in constructor and create a global object of the class. When the object is created, constructor is called and “GeeksforGeeks” is printed.
    #include <iostream>
    
    class MyClass {
    public:
        MyClass()
        {
            std::cout << "GeeksforGeeks";
        }
    } m;
    
    int main()
    {
    }
    

    Output:

    GeeksforGeeks
  2. The idea is to create struct and use the same logic which is discussed in above. The reason is that struct and class in C++ are exactly the same data structure except struct default to public visibility while class defaults to private visibility
    #include <iostream>
    
    struct Mystruct {
    
        Mystruct()
        {
            std::cout << "GeeksforGeeks";
        }
    } obj;
    
    int main() {}
    

    Output:

    GeeksforGeeks
  3. By using global variable, idea is to initialise printf() function to global variable, but it will work only in C++ language as in C language we can’t initialise variable or expression like this to global variable.
    #include <cstdio>
    
    int var = printf("GeeksforGeeks");
    
    int main()
    {
    }
    

    Output:

    GeeksforGeeks

Java language

The idea is to use static block for printing, actually any static blocks declared outside the main() method in java is executed before the main method.

class Myjava {
    static
    {
        System.out.println("GeeksforGeeks");
    }
    public static void main(String args[])
    {
    }
}

Output:

GeeksforGeeks

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