Question

C++

If you tried to compile a source file that doesn't contain a main() function, would this error be detected by the preprocessor, the compiler, or the linker? Briefly justify your answer.

Hint: think about how the files that don't have main() get processed in a project with multiple files. Alternatively, try it out and look at the error message you get.

Answer 1

C++ program without main function

• In C++, programs cannot be executed without the main function, though by using preprocessor directives or source code define with arguments facilitates the program run without main function.
• There are three methods that assist to process C++ program without the main function  

1. Macro Arguments
2. Static initializer
3. Start function

Let's check with the Code:

1.Macro Arguments

#include<stdio.h> 
#define str main 
int str(void) 
{ 
        printf("Hello! Me without main"); 
        return 0; 
}

Here, A macro which defines the main

# define str main

The output:

Hello! Me without main

2. Static initializer

// Program without using main function
#include <iostream>

int execute()
{
        std::cout << "Int run()";
        exit(EXIT_SUCCESS);
}

static int s = execute();

int main()
{
        std::cout << "Int run() - never executed";
}

The Output:

  Int run()

3. Start function

/* Program without using main function */


#include <stdio.h>

void _start()
{
    printf("Run the program without main !");
    exit(0);
}

Here, start function would facilitate run program without main function.