Precision

src/lib_json/json_writer.cpp

@@ -133,17 +133,20 @@ std::string valueToString(UInt value) {
 
 #endif // # if defined(JSON_HAS_INT64)
 
-std::string valueToString(double value, bool useSpecialFloats) {
+std::string valueToString(double value, bool useSpecialFloats, unsigned int precision) {
   // Allocate a buffer that is more than large enough to store the 16 digits of
   // precision requested below.
   char buffer[32];
   int len = -1;
 
+  char formatString[6];
+  sprintf(formatString, "%%.%dg", precision);
+
   // Print into the buffer. We need not request the alternative representation
   // that always has a decimal point because JSON doesn't distingish the
   // concepts of reals and integers.
   if (isfinite(value)) {
-    len = snprintf(buffer, sizeof(buffer), "%.17g", value);
+    len = snprintf(buffer, sizeof(buffer), formatString, value);
   } else {
     // IEEE standard states that NaN values will not compare to themselves
     if (value != value) {
@@ -160,7 +163,7 @@ std::string valueToString(double value, bool useSpecialFloats) {
   return buffer;
 }
 
-std::string valueToString(double value) { return valueToString(value, false); }
+std::string valueToString(double value) { return valueToString(value, false, 17); }
 
 std::string valueToString(bool value) { return value ? "true" : "false"; }
 
@@ -832,7 +835,8 @@ struct BuiltStyledStreamWriter : public StreamWriter
       std::string const& colonSymbol,
       std::string const& nullSymbol,
       std::string const& endingLineFeedSymbol,
-      bool useSpecialFloats);
+      bool useSpecialFloats,
+      unsigned int precision);
   int write(Value const& root, std::ostream* sout) override;
 private:
   void writeValue(Value const& value);
@@ -860,14 +864,16 @@ struct BuiltStyledStreamWriter : public StreamWriter
   bool addChildValues_ : 1;
   bool indented_ : 1;
   bool useSpecialFloats_ : 1;
+  unsigned int precision_;
 };
 BuiltStyledStreamWriter::BuiltStyledStreamWriter(
       std::string const& indentation,
       CommentStyle::Enum cs,
       std::string const& colonSymbol,
       std::string const& nullSymbol,
       std::string const& endingLineFeedSymbol,
-      bool useSpecialFloats)
+      bool useSpecialFloats,
+      unsigned int precision)
   : rightMargin_(74)
   , indentation_(indentation)
   , cs_(cs)
@@ -877,6 +883,7 @@ BuiltStyledStreamWriter::BuiltStyledStreamWriter(
   , addChildValues_(false)
   , indented_(false)
   , useSpecialFloats_(useSpecialFloats)
+  , precision_(precision)
 {
 }
 int BuiltStyledStreamWriter::write(Value const& root, std::ostream* sout)
@@ -906,7 +913,7 @@ void BuiltStyledStreamWriter::writeValue(Value const& value) {
     pushValue(valueToString(value.asLargestUInt()));
     break;
   case realValue:
-    pushValue(valueToString(value.asDouble(), useSpecialFloats_));
+    pushValue(valueToString(value.asDouble(), useSpecialFloats_, precision_));
     break;
   case stringValue:
   {
@@ -1121,6 +1128,7 @@ StreamWriter* StreamWriterBuilder::newStreamWriter() const
   bool eyc = settings_["enableYAMLCompatibility"].asBool();
   bool dnp = settings_["dropNullPlaceholders"].asBool();
   bool usf = settings_["useSpecialFloats"].asBool(); 
+  unsigned int pre = settings_["precision"].asUInt();
   CommentStyle::Enum cs = CommentStyle::All;
   if (cs_str == "All") {
     cs = CommentStyle::All;
@@ -1139,10 +1147,11 @@ StreamWriter* StreamWriterBuilder::newStreamWriter() const
   if (dnp) {
     nullSymbol = "";
   }
+  if (pre > 17) pre = 17;
   std::string endingLineFeedSymbol = "";
   return new BuiltStyledStreamWriter(
       indentation, cs,
-      colonSymbol, nullSymbol, endingLineFeedSymbol, usf);
+      colonSymbol, nullSymbol, endingLineFeedSymbol, usf, pre);
 }
 static void getValidWriterKeys(std::set<std::string>* valid_keys)
 {
@@ -1152,6 +1161,7 @@ static void getValidWriterKeys(std::set<std::string>* valid_keys)
   valid_keys->insert("enableYAMLCompatibility");
   valid_keys->insert("dropNullPlaceholders");
   valid_keys->insert("useSpecialFloats");
+  valid_keys->insert("precision");
 }
 bool StreamWriterBuilder::validate(Json::Value* invalid) const
 {
@@ -1183,6 +1193,7 @@ void StreamWriterBuilder::setDefaults(Json::Value* settings)
   (*settings)["enableYAMLCompatibility"] = false;
   (*settings)["dropNullPlaceholders"] = false;
   (*settings)["useSpecialFloats"] = false;
+  (*settings)["precision"] = 17;
   //! [StreamWriterBuilderDefaults]
 }
 

src/test_lib_json/main.cpp

@@ -1675,6 +1675,43 @@ JSONTEST_FIXTURE(ValueTest, specialFloats) {
   JSONTEST_ASSERT_STRING_EQUAL(expected, result);
 }
 
+JSONTEST_FIXTURE(ValueTest, precision) {
+    Json::StreamWriterBuilder b;
+    b.settings_["precision"] = 5;
+
+    Json::Value v = 100.0/3;
+    std::string expected = "33.333";
+    std::string result = Json::writeString(b, v);
+    JSONTEST_ASSERT_STRING_EQUAL(expected, result);
+
+    v = 0.25000000;
+    expected = "0.25";
+    result = Json::writeString(b, v);
+    JSONTEST_ASSERT_STRING_EQUAL(expected, result);
+
+    v = 0.2563456;
+    expected = "0.25635";
+    result = Json::writeString(b, v);
+    JSONTEST_ASSERT_STRING_EQUAL(expected, result);
+
+    b.settings_["precision"] = 1;
+    expected = "0.3";
+    result = Json::writeString(b, v);
+    JSONTEST_ASSERT_STRING_EQUAL(expected, result);
+
+    b.settings_["precision"] = 17;
+    v = 1234857476305.256345694873740545068;
+    expected = "1234857476305.2563";
+    result = Json::writeString(b, v);
+    JSONTEST_ASSERT_STRING_EQUAL(expected, result);
+
+    b.settings_["precision"] = 24;
+    v = 0.256345694873740545068;
+    expected = "0.25634569487374054";
+    result = Json::writeString(b, v);
+    JSONTEST_ASSERT_STRING_EQUAL(expected, result);
+}
+
 struct WriterTest : JsonTest::TestCase {};
 
 JSONTEST_FIXTURE(WriterTest, dropNullPlaceholders) {
@@ -2489,6 +2526,7 @@ int main(int argc, const char* argv[]) {
   JSONTEST_REGISTER_FIXTURE(runner, ValueTest, zeroes);
   JSONTEST_REGISTER_FIXTURE(runner, ValueTest, zeroesInKeys);
   JSONTEST_REGISTER_FIXTURE(runner, ValueTest, specialFloats);
+  JSONTEST_REGISTER_FIXTURE(runner, ValueTest, precision);
 
   JSONTEST_REGISTER_FIXTURE(runner, WriterTest, dropNullPlaceholders);
   JSONTEST_REGISTER_FIXTURE(runner, StreamWriterTest, dropNullPlaceholders);