What happens if you inline a function that calls it self in C-CodePudding

First I thought the compile time would take forever, or I take a weird error, but that didn't happen. The code runs for a while and then crashes.

This is my code:

#include <iostream>

inline void say_hello()
{
    std::cout << "hello\n";
    say_hello();
}

int main()
{
    say_hello();
}

I thought the compiler will convert it to something like this:

#include <iostream>

int main()
{
    std::cout << "hello\n";
    std::cout << "hello\n";
    std::cout << "hello\n";
    std::cout << "hello\n";
    std::cout << "hello\n";
    std::cout << "hello\n";
    std::cout << "hello\n";
    std::cout << "hello\n";
    std::cout << "hello\n";
    std::cout << "hello\n";
    std::cout << "hello\n";
    std::cout << "hello\n";
    std::cout << "hello\n";
    std::cout << "hello\n";
    std::cout << "hello\n";
    // and crash because my storage is filled
}

But, I think the compiler ignored the inline keyword.

CodePudding user response：

In modern C , the inline specifier is only a suggestion to the compiler that you might want to inline the function. The compiler is not required to comply.

For your specific compiler, please see Visual Studio Inline Functions (C ). You seem to "want" the __forceinline decorator combined with #pragma inline_recursion(on). This will inline to a depth of 16, but that is modifiable as well. I hope it's obvious why this is all a bad idea. Note that this is ALL compiler specific and does not apply to gcc.

__forceinline can fail for a variety of reasons, but the ones that might apply to you:

the function is recursive (what you have) and #pragma inline_recursion(on) is not set
the program is compiled with /Ob0 (the default for debug builds, which you might have set)

If you want to recurse to a level different than 16 (the default), you can use the inline_depth pragma to specify.

Your function would end up looking like this (untested):

#include <iostream>

#pragma inline_depth(9000)
#pragma inline_recursion(on)
__forceinline void say_hello()
{
    std::cout << "hello\n";
    say_hello();
}

int main()
{
    say_hello();
}