Add std::format to string formatting benchmarks

Currently only MSVC supports std::format, so the documented benchmarks
are not updated (they are generated with GCC on Linux).

Author: trflynn89

bench/string/README.md

@@ -1,6 +1,6 @@
-# JSON Parser
+# String formatting
 
-Benchmark of the libfly JSON parser against the popular {fmt} library and the STL:
+Benchmark of the libfly string formatter against the popular {fmt} library and the STL:
 
 * [libfly](/fly/types/string/string.hpp)
 * [{fmt}](https://github.com/fmtlib/fmt)
@@ -11,19 +11,19 @@ All results below are the median of 1000001 iterations of creating a formatted s
 
 ### Formatting with floats
 
-| Formatter      | Duration (ns) |
-| :--            |           --: |
-| libfly         |         1.093 |
-| {fmt}          |         0.609 |
-| STL IO Streams |         1.812 |
+| Formatter         | Duration (ns) |
+| :--               |           --: |
+| libfly            |         1.093 |
+| {fmt}             |         0.609 |
+| std::stringstream |         1.812 |
 
 ### Formatting without floats
 
-| Formatter      | Duration (ns) |
-| :--            |           --: |
-| libfly         |         0.665 |
-| {fmt}          |         0.411 |
-| STL IO Streams |         1.011 |
+| Formatter         | Duration (ns) |
+| :--               |           --: |
+| libfly            |         0.665 |
+| {fmt}             |         0.411 |
+| std::stringstream |         1.011 |
 
 ## Profiles
 

bench/string/benchmark_string.cpp

@@ -10,6 +10,10 @@
 #include <sstream>
 #include <string>
 
+#if __has_include(<format>)
+#    include <format>
+#endif
+
 namespace {
 
 using StringTable = fly::benchmark::Table<std::string, double>;
@@ -69,8 +73,29 @@ class FmtFormat : public StringBase
     }
 };
 
+#if __has_include(<format>)
+
+// std::format
+class StdFormat : public StringBase
+{
+public:
+    void format_with_floats() override
+    {
+        FLY_UNUSED(
+            std::format("{:.10f}:{:04}:{:+}:{}:{}:{}:%\n", 1.234, 42, 3.13, "str", nullptr, 'X'));
+    }
+
+    void format_without_floats() override
+    {
+        FLY_UNUSED(
+            std::format("{:10}:{:04}:{:+}:{}:{}:{}:%\n", 1234, 42, 313, "str", nullptr, 'X'));
+    }
+};
+
+#endif
+
 // STL IO Streams
-class STLStreamFormat : public StringBase
+class StreamFormat : public StringBase
 {
 public:
     void format_with_floats() override
@@ -99,7 +124,10 @@ void run_format_test(std::string &&name)
     std::map<std::string, std::unique_ptr<StringBase>> formatters;
 #if !defined(FLY_PROFILE)
     formatters.emplace("{fmt}", std::make_unique<FmtFormat>());
-    formatters.emplace("STL IO Streams", std::make_unique<STLStreamFormat>());
+    formatters.emplace("std::stringstream", std::make_unique<StreamFormat>());
+#    if __has_include(<format>)
+    formatters.emplace("std::format", std::make_unique<StdFormat>());
+#    endif
 #endif
     formatters.emplace("libfly", std::make_unique<LibflyFormat>());