从另一个函数调用 main

Question

I am new to C, so forgive me if this query is basic.

I want to call main() from another function, and make the program run infinitely. The code is here:

#include <stdio.h>

void message();

int main()
{
    message();

    return 0;
}

void message()
{
    printf("This is a test message. \n");

    main();
}

I expect to see this program run infinitely. However, it runs for some time and then stops suddenly. Using a counter variable, which I printed alongside the test message, I found that the statement "This is a test message." is printed 174608 times after which I get an error message

Segmentation fault (core dumped)

and the program terminates. What does this error mean? And why does the program only run 174608 times (why not infinitely)?

Answer 1

You have stack overflow from infinite recursion. Make infinite loop in main :

int main()
{
  while (1)
  {
    //...
  }
}

Answer 2

The mutual recursion costs stack space. If you put the recursion in main() itself, the compiler may recognise the tail recursion , and replace it by iteration. [for fun and education, don't try this at home, children ...] :

#include <stdio.h>      

void message(); 

int main()
{
    message();  

    return main();
}       

void message()  
{       
    printf("This is a test message. \n");
}

GCC recognises the tail recursion in optimisation level=2 and above. main.s output for gcc -O2 -S main.c:

        .p2align 4,,15
.globl main
        .type   main, @function
main:
        pushl   %ebp
        movl    %esp, %ebp
        andl    $-16, %esp
        .p2align 4,,7
        .p2align 3
.L4:
        call    message
        jmp     .L4
        .size   main, .-main
        .ident  "GCC: (Ubuntu 4.4.3-4ubuntu5.1) 4.4.3"
        .section        .note.GNU-stack,"",@progbits

Answer 3

This is not equivalent to while(1) {...} or for(;;) {...} , which give you infinite loops.

Every time a function(for example, main() or message() ) is called, some values are pushed into the stack . When functions are called too many times, your stack get filled, and finally overflow, giving you a "stack overflow" error.

Note that this error has nothing to do with this site, although they happen to have the same name :)