🚀 go-pugleaf

typedef struct{double re,im;} complex;
class Complex{public:double re,im;
    inline void operator=(Complex&X){re=X.re; im=X.im;};};
void zxcvbnm(int n,...){n=1;}
main(){complex c; Complex C;
zxcvbnm(1,c);
zxcvbnm(1,C);}

After an unexpected compiler error remark in compiling a program, I compiled
this test program with a recent version of Gnu C++, and I got this error:-

t$$.cc: In function `int  main()':
t$$.cc:7: warning: cannot pass objects of type `Complex' through `...'

Why does '...' accept structs but not classes? I have found nothing in (two
good Gnu C++ manuals that I have) about restrictions about what can be passed
through '...'. What other restrictions are there about '...'?