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1#ifndef TEST_SUPPORT_FORMAT_STRING_H2#define TEST_SUPPORT_FORMAT_STRING_H3 4#include <cstdio>5#include <string>6#include <memory>7#include <array>8#include <cstdarg>9 10namespace format_string_detail {11inline std::string format_string_imp(const char* msg, ...) {12 // we might need a second shot at this, so pre-emptively make a copy13 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 expansion43 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 overflow50 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 56const char* unwrap(std::string& s) { return s.c_str(); }57template <class Arg>58Arg 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_detail64 65template <class... Args>66std::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_HPP72