This function is intended to be used by libraries based on GVariant
that want to provide g_variant_get()-like functionality to their
users.
The API is more general than g_variant_get() to allow a wider range
of possible uses.
format_string must still point to a valid format string, but it only
need to be nul-terminated if endptr is NULL. If endptr is
non-NULL then it is updated to point to the first character past the
end of the format string.
app is a pointer to a va_list. The arguments, according to
format_string, are collected from this va_list and the list is left
pointing to the argument following the last.
These two generalisations allow mixing of multiple calls to
g_variant_new_va() and g_variant_get_va() within a single actual
varargs call by the user.
Since 2.24
This function is intended to be used by libraries based on GVariant that want to provide g_variant_get()-like functionality to their users. The API is more general than g_variant_get() to allow a wider range of possible uses. format_string must still point to a valid format string, but it only need to be nul-terminated if endptr is NULL. If endptr is non-NULL then it is updated to point to the first character past the end of the format string. app is a pointer to a va_list. The arguments, according to format_string, are collected from this va_list and the list is left pointing to the argument following the last. These two generalisations allow mixing of multiple calls to g_variant_new_va() and g_variant_get_va() within a single actual varargs call by the user. Since 2.24