Function svn_stringbuf_createv 

pub unsafe extern "C" fn svn_stringbuf_createv(
    pool: *mut apr_pool_t,
    fmt: *const c_char,
    ap: *mut __va_list_tag,
) -> *mut svn_stringbuf_t

Create a new stringbuf by printf-style formatting using @c fmt and @a ap. This is the same as svn_stringbuf_createf() except for the different way of passing the variable arguments.