libcxx/test/support/format_string.h

   1 #ifndef TEST_SUPPORT_FORMAT_STRING_H
   2 #define TEST_SUPPORT_FORMAT_STRING_H
   3
   4 #include <cstdio>
   5 #include <string>
   6 #include <memory>
   7 #include <array>
   8 #include <cstdarg>
   9
  10 namespace format_string_detail {
  11 inline std::string format_string_imp(const char* msg, ...) {
  12   // we might need a second shot at this, so pre-emptively make a copy
  13   struct GuardVAList {
  14     va_list& xtarget;
  15     bool active;
  16     GuardVAList(va_list& val) : xtarget(val), active(true) {}
  17
  18     void clear() {
  19       if (active)
  20         va_end(xtarget);
  21       active = false;
  22     }
  23     ~GuardVAList() {
  24       if (active)
  25         va_end(xtarget);
  26     }
  27   };
  28   va_list args;
  29   va_start(args, msg);
  30   GuardVAList args_guard(args);
  31
  32   va_list args_cp;
  33   va_copy(args_cp, args);
  34   GuardVAList args_copy_guard(args_cp);
  35
  36   std::array<char, 256> local_buff;
  37   std::size_t size = local_buff.size();
  38   auto ret = ::vsnprintf(local_buff.data(), size, msg, args_cp);
  39
  40   args_copy_guard.clear();
  41
  42   // handle empty expansion
  43   if (ret == 0)
  44     return std::string{};
  45   if (static_cast<std::size_t>(ret) < size)
  46     return std::string(local_buff.data());
  47
  48   // we did not provide a long enough buffer on our first attempt.
  49   // add 1 to size to account for null-byte in size cast to prevent overflow
  50   size = static_cast<std::size_t>(ret) + 1;
  51   auto buff_ptr = std::unique_ptr<char[]>(new char[size]);
  52   ret = ::vsnprintf(buff_ptr.get(), size, msg, args);
  53   return std::string(buff_ptr.get());
  54 }
  55
  56 const char* unwrap(std::string& s) { return s.c_str(); }
  57 template <class Arg>
  58 Arg const& unwrap(Arg& a) {
  59   static_assert(!std::is_class<Arg>::value, "cannot pass class here");
  60   return a;
  61 }
  62
  63 } // namespace format_string_detail
  64
  65 template <class... Args>
  66 std::string format_string(const char* fmt, Args const&... args) {
  67   return format_string_detail::format_string_imp(
  68       fmt, format_string_detail::unwrap(const_cast<Args&>(args))...);
  69 }
  70
  71 #endif // TEST_SUPPORT_FORMAT_STRING_HPP