Example to printf() doubles for #68.

src/example/json/printf_doubles.cpp

@@ -0,0 +1,41 @@
+// Copyright (c) 2019 Dr. Colin Hirsch and Daniel Frey
+// Please see LICENSE for license or visit https://github.com/taocpp/json/
+
+#include <cstdio>
+#include <iostream>
+
+#include <tao/json.hpp>
+
+namespace tao::json::events
+{
+   struct printf_doubles
+      : public to_stream
+   {
+      using to_stream::to_stream;
+
+      void number( const double v )
+      {
+         next();
+         if( !std::isfinite( v ) ) {
+            // if this throws, consider using non_finite_to_* transformers
+            throw std::runtime_error( "non-finite double value invalid for JSON string representation" );
+         }
+         char buffer[ 32 ];
+         const std::size_t n = std::snprintf( buffer, sizeof( buffer ), "%0.2f", v );
+         os.write( buffer, n );
+      }
+   };
+
+}  // namespace tao::json::events
+
+int main( int argc, char** argv )
+{
+   if( argc != 2 ) {
+      std::cerr << "usage: " << argv[ 0 ] << " file.json" << std::endl;
+      std::cerr << "  parses the json file and writes it to stdout with '%0.2f' for doubles" << std::endl;
+      return 1;
+   }
+   tao::json::events::printf_doubles consumer( std::cout );
+   tao::json::events::from_file( consumer, argv[ 1 ] );
+   return 0;
+}