// Formatting library for C++ - printf tests // // Copyright (c) 2012 - present, Victor Zverovich // All rights reserved. // // For the license information refer to format.h. #include "fmt/printf.h" #include #include #include #include "fmt/core.h" #include "gtest-extra.h" #include "util.h" using fmt::format; using fmt::format_error; using fmt::detail::max_value; const unsigned BIG_NUM = INT_MAX + 1u; // Makes format string argument positional. static std::string make_positional(fmt::string_view format) { std::string s(format.data(), format.size()); s.replace(s.find('%'), 1, "%1$"); return s; } static std::wstring make_positional(fmt::wstring_view format) { std::wstring s(format.data(), format.size()); s.replace(s.find(L'%'), 1, L"%1$"); return s; } // A wrapper around fmt::sprintf to workaround bogus warnings about invalid // format strings in MSVC. template std::string test_sprintf(fmt::string_view format, const Args&... args) { return fmt::sprintf(format, args...); } template std::wstring test_sprintf(fmt::wstring_view format, const Args&... args) { return fmt::sprintf(format, args...); } #define EXPECT_PRINTF(expected_output, format, arg) \ EXPECT_EQ(expected_output, test_sprintf(format, arg)) \ << "format: " << format; \ EXPECT_EQ(expected_output, fmt::sprintf(make_positional(format), arg)) TEST(PrintfTest, NoArgs) { EXPECT_EQ("test", test_sprintf("test")); EXPECT_EQ(L"test", fmt::sprintf(L"test")); } TEST(PrintfTest, Escape) { EXPECT_EQ("%", test_sprintf("%%")); EXPECT_EQ("before %", test_sprintf("before %%")); EXPECT_EQ("% after", test_sprintf("%% after")); EXPECT_EQ("before % after", test_sprintf("before %% after")); EXPECT_EQ("%s", test_sprintf("%%s")); EXPECT_EQ(L"%", fmt::sprintf(L"%%")); EXPECT_EQ(L"before %", fmt::sprintf(L"before %%")); EXPECT_EQ(L"% after", fmt::sprintf(L"%% after")); EXPECT_EQ(L"before % after", fmt::sprintf(L"before %% after")); EXPECT_EQ(L"%s", fmt::sprintf(L"%%s")); } TEST(PrintfTest, PositionalArgs) { EXPECT_EQ("42", test_sprintf("%1$d", 42)); EXPECT_EQ("before 42", test_sprintf("before %1$d", 42)); EXPECT_EQ("42 after", test_sprintf("%1$d after", 42)); EXPECT_EQ("before 42 after", test_sprintf("before %1$d after", 42)); EXPECT_EQ("answer = 42", test_sprintf("%1$s = %2$d", "answer", 42)); EXPECT_EQ("42 is the answer", test_sprintf("%2$d is the %1$s", "answer", 42)); EXPECT_EQ("abracadabra", test_sprintf("%1$s%2$s%1$s", "abra", "cad")); } TEST(PrintfTest, AutomaticArgIndexing) { EXPECT_EQ("abc", test_sprintf("%c%c%c", 'a', 'b', 'c')); } TEST(PrintfTest, NumberIsTooBigInArgIndex) { EXPECT_THROW_MSG(test_sprintf(format("%{}$", BIG_NUM)), format_error, "number is too big"); EXPECT_THROW_MSG(test_sprintf(format("%{}$d", BIG_NUM)), format_error, "number is too big"); } TEST(PrintfTest, SwitchArgIndexing) { EXPECT_THROW_MSG(test_sprintf("%1$d%", 1, 2), format_error, "cannot switch from manual to automatic argument indexing"); EXPECT_THROW_MSG(test_sprintf(format("%1$d%{}d", BIG_NUM), 1, 2), format_error, "number is too big"); EXPECT_THROW_MSG(test_sprintf("%1$d%d", 1, 2), format_error, "cannot switch from manual to automatic argument indexing"); EXPECT_THROW_MSG(test_sprintf("%d%1$", 1, 2), format_error, "cannot switch from automatic to manual argument indexing"); EXPECT_THROW_MSG(test_sprintf(format("%d%{}$d", BIG_NUM), 1, 2), format_error, "number is too big"); EXPECT_THROW_MSG(test_sprintf("%d%1$d", 1, 2), format_error, "cannot switch from automatic to manual argument indexing"); // Indexing errors override width errors. EXPECT_THROW_MSG(test_sprintf(format("%d%1${}d", BIG_NUM), 1, 2), format_error, "number is too big"); EXPECT_THROW_MSG(test_sprintf(format("%1$d%{}d", BIG_NUM), 1, 2), format_error, "number is too big"); } TEST(PrintfTest, InvalidArgIndex) { EXPECT_THROW_MSG(test_sprintf("%0$d", 42), format_error, "argument not found"); EXPECT_THROW_MSG(test_sprintf("%2$d", 42), format_error, "argument not found"); EXPECT_THROW_MSG(test_sprintf(format("%{}$d", INT_MAX), 42), format_error, "argument not found"); EXPECT_THROW_MSG(test_sprintf("%2$", 42), format_error, "argument not found"); EXPECT_THROW_MSG(test_sprintf(format("%{}$d", BIG_NUM), 42), format_error, "number is too big"); } TEST(PrintfTest, DefaultAlignRight) { EXPECT_PRINTF(" 42", "%5d", 42); EXPECT_PRINTF(" abc", "%5s", "abc"); } TEST(PrintfTest, ZeroFlag) { EXPECT_PRINTF("00042", "%05d", 42); EXPECT_PRINTF("-0042", "%05d", -42); EXPECT_PRINTF("00042", "%05d", 42); EXPECT_PRINTF("-0042", "%05d", -42); EXPECT_PRINTF("-004.2", "%06g", -4.2); EXPECT_PRINTF("+00042", "%00+6d", 42); EXPECT_PRINTF(" 42", "%05.d", 42); EXPECT_PRINTF(" 0042", "%05.4d", 42); // '0' flag is ignored for non-numeric types. EXPECT_PRINTF(" x", "%05c", 'x'); } TEST(PrintfTest, PlusFlag) { EXPECT_PRINTF("+42", "%+d", 42); EXPECT_PRINTF("-42", "%+d", -42); EXPECT_PRINTF("+0042", "%+05d", 42); EXPECT_PRINTF("+0042", "%0++5d", 42); // '+' flag is ignored for non-numeric types. EXPECT_PRINTF("x", "%+c", 'x'); // '+' flag wins over space flag EXPECT_PRINTF("+42", "%+ d", 42); EXPECT_PRINTF("-42", "%+ d", -42); EXPECT_PRINTF("+42", "% +d", 42); EXPECT_PRINTF("-42", "% +d", -42); EXPECT_PRINTF("+0042", "% +05d", 42); EXPECT_PRINTF("+0042", "%0+ 5d", 42); // '+' flag and space flag are both ignored for non-numeric types. EXPECT_PRINTF("x", "%+ c", 'x'); EXPECT_PRINTF("x", "% +c", 'x'); } TEST(PrintfTest, MinusFlag) { EXPECT_PRINTF("abc ", "%-5s", "abc"); EXPECT_PRINTF("abc ", "%0--5s", "abc"); EXPECT_PRINTF("7 ", "%-5d", 7); EXPECT_PRINTF("97 ", "%-5hhi", 'a'); EXPECT_PRINTF("a ", "%-5c", 'a'); // '0' flag is ignored if '-' flag is given EXPECT_PRINTF("7 ", "%-05d", 7); EXPECT_PRINTF("7 ", "%0-5d", 7); EXPECT_PRINTF("a ", "%-05c", 'a'); EXPECT_PRINTF("a ", "%0-5c", 'a'); EXPECT_PRINTF("97 ", "%-05hhi", 'a'); EXPECT_PRINTF("97 ", "%0-5hhi", 'a'); // '-' and space flag don't interfere EXPECT_PRINTF(" 42", "%- d", 42); } TEST(PrintfTest, SpaceFlag) { EXPECT_PRINTF(" 42", "% d", 42); EXPECT_PRINTF("-42", "% d", -42); EXPECT_PRINTF(" 0042", "% 05d", 42); EXPECT_PRINTF(" 0042", "%0 5d", 42); // ' ' flag is ignored for non-numeric types. EXPECT_PRINTF("x", "% c", 'x'); } TEST(PrintfTest, HashFlag) { EXPECT_PRINTF("042", "%#o", 042); EXPECT_PRINTF(fmt::format("0{:o}", static_cast(-042)), "%#o", -042); EXPECT_PRINTF("0", "%#o", 0); EXPECT_PRINTF("0x42", "%#x", 0x42); EXPECT_PRINTF("0X42", "%#X", 0x42); EXPECT_PRINTF(fmt::format("0x{:x}", static_cast(-0x42)), "%#x", -0x42); EXPECT_PRINTF("0", "%#x", 0); EXPECT_PRINTF("0x0042", "%#06x", 0x42); EXPECT_PRINTF("0x0042", "%0##6x", 0x42); EXPECT_PRINTF("-42.000000", "%#f", -42.0); EXPECT_PRINTF("-42.000000", "%#F", -42.0); char buffer[BUFFER_SIZE]; safe_sprintf(buffer, "%#e", -42.0); EXPECT_PRINTF(buffer, "%#e", -42.0); safe_sprintf(buffer, "%#E", -42.0); EXPECT_PRINTF(buffer, "%#E", -42.0); EXPECT_PRINTF("-42.0000", "%#g", -42.0); EXPECT_PRINTF("-42.0000", "%#G", -42.0); safe_sprintf(buffer, "%#a", 16.0); EXPECT_PRINTF(buffer, "%#a", 16.0); safe_sprintf(buffer, "%#A", 16.0); EXPECT_PRINTF(buffer, "%#A", 16.0); // '#' flag is ignored for non-numeric types. EXPECT_PRINTF("x", "%#c", 'x'); } TEST(PrintfTest, Width) { EXPECT_PRINTF(" abc", "%5s", "abc"); // Width cannot be specified twice. EXPECT_THROW_MSG(test_sprintf("%5-5d", 42), format_error, "invalid type specifier"); EXPECT_THROW_MSG(test_sprintf(format("%{}d", BIG_NUM), 42), format_error, "number is too big"); EXPECT_THROW_MSG(test_sprintf(format("%1${}d", BIG_NUM), 42), format_error, "number is too big"); } TEST(PrintfTest, DynamicWidth) { EXPECT_EQ(" 42", test_sprintf("%*d", 5, 42)); EXPECT_EQ("42 ", test_sprintf("%*d", -5, 42)); EXPECT_THROW_MSG(test_sprintf("%*d", 5.0, 42), format_error, "width is not integer"); EXPECT_THROW_MSG(test_sprintf("%*d"), format_error, "argument not found"); EXPECT_THROW_MSG(test_sprintf("%*d", BIG_NUM, 42), format_error, "number is too big"); } TEST(PrintfTest, IntPrecision) { EXPECT_PRINTF("00042", "%.5d", 42); EXPECT_PRINTF("-00042", "%.5d", -42); EXPECT_PRINTF("00042", "%.5x", 0x42); EXPECT_PRINTF("0x00042", "%#.5x", 0x42); EXPECT_PRINTF("00042", "%.5o", 042); EXPECT_PRINTF("00042", "%#.5o", 042); EXPECT_PRINTF(" 00042", "%7.5d", 42); EXPECT_PRINTF(" 00042", "%7.5x", 0x42); EXPECT_PRINTF(" 0x00042", "%#10.5x", 0x42); EXPECT_PRINTF(" 00042", "%7.5o", 042); EXPECT_PRINTF(" 00042", "%#10.5o", 042); EXPECT_PRINTF("00042 ", "%-7.5d", 42); EXPECT_PRINTF("00042 ", "%-7.5x", 0x42); EXPECT_PRINTF("0x00042 ", "%-#10.5x", 0x42); EXPECT_PRINTF("00042 ", "%-7.5o", 042); EXPECT_PRINTF("00042 ", "%-#10.5o", 042); } TEST(PrintfTest, FloatPrecision) { char buffer[BUFFER_SIZE]; safe_sprintf(buffer, "%.3e", 1234.5678); EXPECT_PRINTF(buffer, "%.3e", 1234.5678); EXPECT_PRINTF("1234.568", "%.3f", 1234.5678); EXPECT_PRINTF("1.23e+03", "%.3g", 1234.5678); safe_sprintf(buffer, "%.3a", 1234.5678); EXPECT_PRINTF(buffer, "%.3a", 1234.5678); } TEST(PrintfTest, StringPrecision) { char test[] = {'H', 'e', 'l', 'l', 'o'}; EXPECT_EQ(fmt::sprintf("%.4s", test), "Hell"); } TEST(PrintfTest, IgnorePrecisionForNonNumericArg) { EXPECT_PRINTF("abc", "%.5s", "abc"); } TEST(PrintfTest, DynamicPrecision) { EXPECT_EQ("00042", test_sprintf("%.*d", 5, 42)); EXPECT_EQ("42", test_sprintf("%.*d", -5, 42)); EXPECT_THROW_MSG(test_sprintf("%.*d", 5.0, 42), format_error, "precision is not integer"); EXPECT_THROW_MSG(test_sprintf("%.*d"), format_error, "argument not found"); EXPECT_THROW_MSG(test_sprintf("%.*d", BIG_NUM, 42), format_error, "number is too big"); if (sizeof(long long) != sizeof(int)) { long long prec = static_cast(INT_MIN) - 1; EXPECT_THROW_MSG(test_sprintf("%.*d", prec, 42), format_error, "number is too big"); } } template struct make_signed { typedef T type; }; #define SPECIALIZE_MAKE_SIGNED(T, S) \ template <> struct make_signed { typedef S type; } SPECIALIZE_MAKE_SIGNED(char, signed char); SPECIALIZE_MAKE_SIGNED(unsigned char, signed char); SPECIALIZE_MAKE_SIGNED(unsigned short, short); SPECIALIZE_MAKE_SIGNED(unsigned, int); SPECIALIZE_MAKE_SIGNED(unsigned long, long); SPECIALIZE_MAKE_SIGNED(unsigned long long, long long); // Test length format specifier ``length_spec``. template void TestLength(const char* length_spec, U value) { long long signed_value = 0; unsigned long long unsigned_value = 0; // Apply integer promotion to the argument. unsigned long long max = max_value(); using fmt::detail::const_check; if (const_check(max <= static_cast(max_value()))) { signed_value = static_cast(value); unsigned_value = static_cast(value); } else if (const_check(max <= max_value())) { signed_value = static_cast(value); unsigned_value = static_cast(value); } if (sizeof(U) <= sizeof(int) && sizeof(int) < sizeof(T)) { signed_value = static_cast(value); unsigned_value = static_cast( static_cast::type>(value)); } else { signed_value = static_cast::type>(value); unsigned_value = static_cast::type>(value); } std::ostringstream os; os << signed_value; EXPECT_PRINTF(os.str(), fmt::format("%{}d", length_spec), value); EXPECT_PRINTF(os.str(), fmt::format("%{}i", length_spec), value); os.str(""); os << unsigned_value; EXPECT_PRINTF(os.str(), fmt::format("%{}u", length_spec), value); os.str(""); os << std::oct << unsigned_value; EXPECT_PRINTF(os.str(), fmt::format("%{}o", length_spec), value); os.str(""); os << std::hex << unsigned_value; EXPECT_PRINTF(os.str(), fmt::format("%{}x", length_spec), value); os.str(""); os << std::hex << std::uppercase << unsigned_value; EXPECT_PRINTF(os.str(), fmt::format("%{}X", length_spec), value); } template void TestLength(const char* length_spec) { T min = std::numeric_limits::min(), max = max_value(); TestLength(length_spec, 42); TestLength(length_spec, -42); TestLength(length_spec, min); TestLength(length_spec, max); long long long_long_min = std::numeric_limits::min(); if (static_cast(min) > long_long_min) TestLength(length_spec, static_cast(min) - 1); unsigned long long long_long_max = max_value(); if (static_cast(max) < long_long_max) TestLength(length_spec, static_cast(max) + 1); TestLength(length_spec, std::numeric_limits::min()); TestLength(length_spec, max_value()); TestLength(length_spec, std::numeric_limits::min()); TestLength(length_spec, max_value()); TestLength(length_spec, std::numeric_limits::min()); TestLength(length_spec, max_value()); TestLength(length_spec, std::numeric_limits::min()); TestLength(length_spec, max_value()); TestLength(length_spec, std::numeric_limits::min()); TestLength(length_spec, max_value()); } TEST(PrintfTest, Length) { TestLength("hh"); TestLength("hh"); TestLength("hh"); TestLength("h"); TestLength("h"); TestLength("l"); TestLength("l"); TestLength("ll"); TestLength("ll"); TestLength("j"); TestLength("z"); TestLength("t"); long double max = max_value(); EXPECT_PRINTF(fmt::format("{:.6}", max), "%g", max); EXPECT_PRINTF(fmt::format("{:.6}", max), "%Lg", max); } TEST(PrintfTest, Bool) { EXPECT_PRINTF("1", "%d", true); EXPECT_PRINTF("true", "%s", true); } TEST(PrintfTest, Int) { EXPECT_PRINTF("-42", "%d", -42); EXPECT_PRINTF("-42", "%i", -42); unsigned u = 0 - 42u; EXPECT_PRINTF(fmt::format("{}", u), "%u", -42); EXPECT_PRINTF(fmt::format("{:o}", u), "%o", -42); EXPECT_PRINTF(fmt::format("{:x}", u), "%x", -42); EXPECT_PRINTF(fmt::format("{:X}", u), "%X", -42); } TEST(PrintfTest, long_long) { // fmt::printf allows passing long long arguments to %d without length // specifiers. long long max = max_value(); EXPECT_PRINTF(fmt::format("{}", max), "%d", max); } TEST(PrintfTest, Float) { EXPECT_PRINTF("392.650000", "%f", 392.65); EXPECT_PRINTF("392.65", "%.2f", 392.65); EXPECT_PRINTF("392.6", "%.1f", 392.65); EXPECT_PRINTF("393", "%.f", 392.65); EXPECT_PRINTF("392.650000", "%F", 392.65); char buffer[BUFFER_SIZE]; safe_sprintf(buffer, "%e", 392.65); EXPECT_PRINTF(buffer, "%e", 392.65); safe_sprintf(buffer, "%E", 392.65); EXPECT_PRINTF(buffer, "%E", 392.65); EXPECT_PRINTF("392.65", "%g", 392.65); EXPECT_PRINTF("392.65", "%G", 392.65); EXPECT_PRINTF("392", "%g", 392.0); EXPECT_PRINTF("392", "%G", 392.0); EXPECT_PRINTF("4.56e-07", "%g", 0.000000456); safe_sprintf(buffer, "%a", -392.65); EXPECT_EQ(buffer, format("{:a}", -392.65)); safe_sprintf(buffer, "%A", -392.65); EXPECT_EQ(buffer, format("{:A}", -392.65)); } TEST(PrintfTest, Inf) { double inf = std::numeric_limits::infinity(); for (const char* type = "fega"; *type; ++type) { EXPECT_PRINTF("inf", fmt::format("%{}", *type), inf); char upper = static_cast(std::toupper(*type)); EXPECT_PRINTF("INF", fmt::format("%{}", upper), inf); } } TEST(PrintfTest, Char) { EXPECT_PRINTF("x", "%c", 'x'); int max = max_value(); EXPECT_PRINTF(fmt::format("{}", static_cast(max)), "%c", max); // EXPECT_PRINTF("x", "%lc", L'x'); EXPECT_PRINTF(L"x", L"%c", L'x'); EXPECT_PRINTF(fmt::format(L"{}", static_cast(max)), L"%c", max); } TEST(PrintfTest, String) { EXPECT_PRINTF("abc", "%s", "abc"); const char* null_str = nullptr; EXPECT_PRINTF("(null)", "%s", null_str); EXPECT_PRINTF(" (null)", "%10s", null_str); EXPECT_PRINTF(L"abc", L"%s", L"abc"); const wchar_t* null_wstr = nullptr; EXPECT_PRINTF(L"(null)", L"%s", null_wstr); EXPECT_PRINTF(L" (null)", L"%10s", null_wstr); } TEST(PrintfTest, UCharString) { unsigned char str[] = "test"; unsigned char* pstr = str; EXPECT_EQ("test", fmt::sprintf("%s", pstr)); } TEST(PrintfTest, Pointer) { int n; void* p = &n; EXPECT_PRINTF(fmt::format("{}", p), "%p", p); p = nullptr; EXPECT_PRINTF("(nil)", "%p", p); EXPECT_PRINTF(" (nil)", "%10p", p); const char* s = "test"; EXPECT_PRINTF(fmt::format("{:p}", s), "%p", s); const char* null_str = nullptr; EXPECT_PRINTF("(nil)", "%p", null_str); p = &n; EXPECT_PRINTF(fmt::format(L"{}", p), L"%p", p); p = nullptr; EXPECT_PRINTF(L"(nil)", L"%p", p); EXPECT_PRINTF(L" (nil)", L"%10p", p); const wchar_t* w = L"test"; EXPECT_PRINTF(fmt::format(L"{:p}", w), L"%p", w); const wchar_t* null_wstr = nullptr; EXPECT_PRINTF(L"(nil)", L"%p", null_wstr); } TEST(PrintfTest, Location) { // TODO: test %n } enum test_enum { answer = 42 }; TEST(PrintfTest, Enum) { EXPECT_PRINTF("42", "%d", answer); volatile test_enum volatile_enum = answer; EXPECT_PRINTF("42", "%d", volatile_enum); } #if FMT_USE_FCNTL TEST(PrintfTest, Examples) { const char* weekday = "Thursday"; const char* month = "August"; int day = 21; EXPECT_WRITE(stdout, fmt::printf("%1$s, %3$d %2$s", weekday, month, day), "Thursday, 21 August"); } TEST(PrintfTest, PrintfError) { fmt::file read_end, write_end; fmt::file::pipe(read_end, write_end); int result = fmt::fprintf(read_end.fdopen("r").get(), "test"); EXPECT_LT(result, 0); } #endif TEST(PrintfTest, WideString) { EXPECT_EQ(L"abc", fmt::sprintf(L"%s", L"abc")); } TEST(PrintfTest, PrintfCustom) { EXPECT_EQ("abc", test_sprintf("%s", TestString("abc"))); } TEST(PrintfTest, OStream) { std::ostringstream os; int ret = fmt::fprintf(os, "Don't %s!", "panic"); EXPECT_EQ("Don't panic!", os.str()); EXPECT_EQ(12, ret); } TEST(PrintfTest, VPrintf) { fmt::format_arg_store as{42}; fmt::basic_format_args args(as); EXPECT_EQ(fmt::vsprintf("%d", args), "42"); EXPECT_WRITE(stdout, fmt::vprintf("%d", args), "42"); EXPECT_WRITE(stdout, fmt::vfprintf(stdout, "%d", args), "42"); EXPECT_WRITE(stdout, fmt::vfprintf(std::cout, "%d", args), "42"); } template void check_format_string_regression(fmt::string_view s, const Args&... args) { fmt::sprintf(s, args...); } TEST(PrintfTest, CheckFormatStringRegression) { check_format_string_regression("%c%s", 'x', ""); } TEST(PrintfTest, FixedLargeExponent) { EXPECT_EQ("1000000000000000000000", fmt::sprintf("%.*f", -13, 1e21)); } TEST(PrintfTest, VSPrintfMakeArgsExample) { fmt::format_arg_store as{42, "something"}; fmt::basic_format_args args(as); EXPECT_EQ("[42] something happened", fmt::vsprintf("[%d] %s happened", args)); auto as2 = fmt::make_printf_args(42, "something"); fmt::basic_format_args args2(as2); EXPECT_EQ("[42] something happened", fmt::vsprintf("[%d] %s happened", args2)); // The older gcc versions can't cast the return value. #if !defined(__GNUC__) || (__GNUC__ > 4) EXPECT_EQ("[42] something happened", fmt::vsprintf("[%d] %s happened", {fmt::make_printf_args(42, "something")})); #endif } TEST(PrintfTest, VSPrintfMakeWArgsExample) { fmt::format_arg_store as{ 42, L"something"}; fmt::basic_format_args args(as); EXPECT_EQ(L"[42] something happened", fmt::vsprintf(L"[%d] %s happened", args)); auto as2 = fmt::make_wprintf_args(42, L"something"); fmt::basic_format_args args2(as2); EXPECT_EQ(L"[42] something happened", fmt::vsprintf(L"[%d] %s happened", args2)); // the older gcc versions can't cast the return value #if !defined(__GNUC__) || (__GNUC__ > 4) EXPECT_EQ(L"[42] something happened", fmt::vsprintf(L"[%d] %s happened", {fmt::make_wprintf_args(42, L"something")})); #endif } typedef fmt::printf_arg_formatter> formatter_t; typedef fmt::basic_printf_context context_t; // A custom printf argument formatter that doesn't print `-` for floating-point // values rounded to 0. class custom_printf_arg_formatter : public formatter_t { public: using formatter_t::iterator; custom_printf_arg_formatter(formatter_t::iterator iter, formatter_t::format_specs& specs, context_t& ctx) : formatter_t(iter, specs, ctx) {} using formatter_t::operator(); #if FMT_MSC_VER > 0 && FMT_MSC_VER <= 1804 template ::value)> iterator operator()(T value){ #else iterator operator()(double value) { #endif // Comparing a float to 0.0 is safe. if (round(value * pow(10, specs()->precision)) == 0.0) value = 0; return formatter_t::operator()(value); } } ; typedef fmt::basic_format_args format_args_t; std::string custom_vformat(fmt::string_view format_str, format_args_t args) { fmt::memory_buffer buffer; fmt::vprintf(buffer, format_str, args); return std::string(buffer.data(), buffer.size()); } template std::string custom_format(const char* format_str, const Args&... args) { auto va = fmt::make_printf_args(args...); return custom_vformat(format_str, {va}); } TEST(PrintfTest, CustomFormat) { EXPECT_EQ("0.00", custom_format("%.2f", -.00001)); EXPECT_EQ("0.00", custom_format("%.2f", .00001)); EXPECT_EQ("1.00", custom_format("%.2f", 1.00001)); EXPECT_EQ("-1.00", custom_format("%.2f", -1.00001)); }