On Friday, 5 August 2016 at 08:32:42 UTC, kink wrote:
On Thursday, 4 August 2016 at 21:03:52 UTC, Mark "J" Twain
wrote:
How can I construct a va_list for vsprintf when all I have is
the a list of pointers to the data, without their type info?
A va_list seems to be a packed struct of values and/or
pointers to the data. While I could construct such a list,
theoretically, I don't always know when I should store an
element as a pointer or a value.
e.g., ints, floats, and other value types seems to get stored
directly in the list, while strings and *other* stuff get
stored as pointers.
I would be nice if a printf variant listed takes only a
pointer list to all the values, does anything like this exist?
If not, is there any standardization of what is a value in the
list and what is a pointer so I can attempt to build the list
properly?
This has absolutely nothing to do with D as these are C
functions, so you'd be better off asking this in another forum.
Anyway, I have no idea why you'd want to construct the va_list
manually. These vprintf() functions only exist so that other
variadic functions can forward THEIR varargs - e.g.,
extern(C) void myOldschoolPrintf(in char* format, ...)
{
doSomethingSpecial();
va_list myVarargs = va_start(format);
vprintf(format, myVarargs);
}
Just a side note, a C nitpicker that I am, you forgot the va_end
after the call to vprintf(). On a lot of platforms it's not a
problem, on Linux/x86_64 (i.e. a very common platform) it's very
likely a memory leak (as the ABI allows to pass parameters in
register even for vararg functions, these registers have to be
saved somewhere to be usable in a va_list).
Note that va_list is highly platform-dependent, so filling the
struct manually is a very bad idea.
Yes indeed, and one of the most common platforms is the very
complex one. It's probably the most common issue when porting C
programs to Linux/x86_64 for the first time.
