Can You Call main() Recursively in C ?

Calling main() within Itself in C

The C standard outlines the main function as the fundamental entry point for every program. However, the question arises: "Is it feasible to call main() from within itself?"

Functional Constraints

According to the C Standard, no. The main function, once defined and executed, marks the beginning and the end of the program. Recursively calling main() violates this fundamental principle.

Practical Implementation

In practice, however, certain compilers like Linux's g allow for the unconventional call of main() within main(). This behavior is not explicitly supported by the standard but is permitted by the compiler's implementation.

For instance, consider the following code:

<code class="c++">#include <iostream>
#include <cstdlib>
using namespace std;

int main() {
    int y = rand() % 10; // random number generation
    cout << "y = " << y << endl;
    return (y == 7) ? 0 : main();
}</code>

This code performs random number generation, and if the generated number is not equal to 7, it recursively calls main().

Assembly-Level Analysis

Examining the assembly code generated by g reveals that main() is invoked just like any other function:

<code class="assembly">main:
        ...
        cmpl    , -12(%rbp)
        je      .L7
        call    main
        ...
.L7:
        ...
        leave
        ret</code>

Compiler Warning

It's worth noting that while g compiles such code, it generates a warning with the -pedantic flag to remind you that it violates the C Standard:

g.cpp:8: error: ISO C++ forbids taking address of function '::main'

Conclusion

While calling main() within itself may work in some situations, it's not officially sanctioned by the C Standard. It's a violation of standard behavior and may lead to undefined results across different compilers and platforms. As such, it's strongly discouraged to rely on this unconventional practice in production code.

The above is the detailed content of Can You Call main() Recursively in C ?. For more information, please follow other related articles on the PHP Chinese website!