I read a little about variadic functions in C/C++ and I found a thread that mentions to reuse a va_list in GCC you need to use a copy of it with va_copy and on the same thread they have suggested defining it with
#define va_copy(d,s) ((d) = (s))
Which means that it is simply assigning the value of va_list s to va_list d.
Wouldn't it be more readable to use va_list ap1 = va_list ap instead? What is the point of creating another function called va_copy?
in GCC you need to use a copy of it with va_copy and on the same thread they have suggested defining it with
#define va_copy(d,s) ((d) = (s))Which means that it is simply assigning the value of va_list s to va_list d.
That's not what they are saying in the other thread. In the J Jorgenson answer they state:
When attempting to reuse a va_list on GCC, one MUST use va_copy(), as the GCC implementation causes the va_list to be modified, causing the pointer to be positioned after last param after use by a v??printf() function.
Which means if you need to make a copy in GCC, you need to use va_copy
The answer that talks about implementing va_copy as
A previous question about the lack of va_copy in MSVC had some decent enough suggestions, including to implement your own version of va_copy for use in MSVC:
#define va_copy(d,s) ((d) = (s))
Is talking about MSVC which does not implement va_copy. The reason you would add such a "usless" macro is so that you can just use va_copy and get the correct behavior in both GCC and MSVC.
Wouldn't it be more readable to use va_list ap1 = va_list ap instead? What is the point of creating another function called va_copy?
Depending on how va_list is implemented it might not be "enough" to just do va_list ap1 = va_list ap. There can be thing that need to happen that can't be done with operator =. For instance, if va_list is a pointer type, you can't overload operator = for it so you need to make a named "function".
