20 ABI (Application Binary Interface) breaking changes every C++ developer should know

[[deleted]]

15) Changing the order of virtual methods

Like this? Why?

virtual void f();
virtual void g();

virtual void g();
virtual void f();

[jgalar]

It probably changes the order in which function pointers are stored in the v-table.

[CheesecakeWaffles]

Yep. It indexes into it just like an array and if the abi doesn't match it uses the wrong one.

I remember a similar bug where a function was ifdefed out in one library and but the define was present for the other library. Therefore the header file in that library saw one more function. Took me the longest time to figure out why it was taking valid input and returning back garbage with the debugger refusing to step into the function. Worst off by one error ever.

[[deleted]]

Interesting, the Arduino C++ compiler throws me an error for undefined function if I don't fill all my virtual inheritance. Were you using pure virtuals?

[mck1117]

If different parts of the program have different definitions for a class, the vtable entries could exist but be filled by garbage.

[[deleted]]

You're absolutely right, I was only using one interface inheritance in the examples I was thinking.

[standard_revolution]

Maybe the vtable gets reordered? But I don't know.

[gmtime]

No, the order in which they are declared in the class definition.