How is FormatString() able to take in variable arguments

[btgvesta]

How is your FormatString() function able to to take in variable arguments?

[bagaffey]

This is using a special system in C called variadic arguments. You can see it in the code here where the ... invokes it.

FormatString(umw DestSize, char* Dest, char* Format, ...)

that ... means this function may take more arguments and at compile time, we do not know how many or what type these argument(s) are AOT (ahead of time).

In order to handle those variadic arguments, C macros are used that come from <stdarg,h>.
Those macros are:

1. va_list: a special type that represents the list of the extra arguments that are passed in.
2. va_start: this initializes va_list -- specifically clarifying where it begins.
3. va_arg: this pulls out the next argument and its type from the list.
4. va_end: this cleans up and clarifies where the variadic list ends.

So, you can see how this is used in the code of the function:

    va_start(ArgList, Format);
    umw Result = FormatStringList(DestSize, Dest, Format, ArgList);
    va_end(ArgList);

That ellipsis (...) allows us to pack up 'the rest of the arguments' and va_arg allows us to unpack them one by one.