Some tweaks:

* Make `json.h` an IWYU import header.
* Change `Reader::parse` to take its `document` parameter as `std::string_view`.
* Add `static void StreamWriterBuilder::updateDefaults(const Json::Value& settings);`
  * Allows to set the global configuration.

Author: helly25

include/json/json.h

@@ -6,10 +6,10 @@
 #ifndef JSON_JSON_H_INCLUDED
 #define JSON_JSON_H_INCLUDED
 
-#include "config.h"
-#include "json_features.h"
-#include "reader.h"
-#include "value.h"
-#include "writer.h"
+#include "config.h"  // IWYU pragma: export
+#include "json_features.h"  // IWYU pragma: export
+#include "reader.h"  // IWYU pragma: export
+#include "value.h"  // IWYU pragma: export
+#include "writer.h"  // IWYU pragma: export
 
 #endif // JSON_JSON_H_INCLUDED

include/json/reader.h

@@ -74,7 +74,7 @@ class JSON_API Reader {
    * \return \c true if the document was successfully parsed, \c false if an
    * error occurred.
    */
-  bool parse(const std::string& document, Value& root,
+  bool parse(std::string_view document, Value& root,
              bool collectComments = true);
 
   /** \brief Read a Value from a <a HREF="http://www.json.org">JSON</a>
@@ -400,6 +400,9 @@ class JSON_API CharReaderBuilder : public CharReader::Factory {
 bool JSON_API parseFromStream(CharReader::Factory const&, IStream&, Value* root,
                               String* errs);
 
+bool JSON_API parseFromString(CharReader::Factory const&, std::string_view,
+                              Value* root, JSONCPP_STRING* errs);
+
 /** \brief Read from 'sin' into 'root'.
  *
  * Always keep comments from the input JSON.

include/json/writer.h

@@ -143,6 +143,7 @@ class JSON_API StreamWriterBuilder : public StreamWriter::Factory {
    * \snippet src/lib_json/json_writer.cpp StreamWriterBuilderDefaults
    */
   static void setDefaults(Json::Value* settings);
+  static void updateDefaults(const Json::Value& settings);
 };
 
 /** \brief Abstract class for writers.

src/lib_json/json_reader.cpp

@@ -78,7 +78,7 @@ Reader::Reader() : features_(Features::all()) {}
 
 Reader::Reader(const Features& features) : features_(features) {}
 
-bool Reader::parse(const std::string& document, Value& root,
+bool Reader::parse(std::string_view document, Value& root,
                    bool collectComments) {
   document_.assign(document.begin(), document.end());
   const char* begin = document_.c_str();
@@ -1992,6 +1992,15 @@ bool parseFromStream(CharReader::Factory const& fact, IStream& sin, Value* root,
   return reader->parse(begin, end, root, errs);
 }
 
+bool parseFromString(
+    CharReader::Factory const& fact, std::string_view doc, Value* root, JSONCPP_STRING* errs) {
+  char const* begin = doc.data();
+  char const* end = begin + doc.size();
+  // Note that we do not actually need a null-terminator.
+  CharReaderPtr const reader(fact.newCharReader());
+  return reader->parse(begin, end, root, errs);
+}
+
 IStream& operator>>(IStream& sin, Value& root) {
   CharReaderBuilder b;
   String errs;

src/lib_json/json_writer.cpp

@@ -1170,18 +1170,30 @@ bool StreamWriterBuilder::validate(Json::Value* invalid) const {
 Value& StreamWriterBuilder::operator[](const String& key) {
   return settings_[key];
 }
-// static
-void StreamWriterBuilder::setDefaults(Json::Value* settings) {
+
+static Json::Value& global_settings_ = *new Json::Value([] {
   //! [StreamWriterBuilderDefaults]
-  (*settings)["commentStyle"] = "All";
-  (*settings)["indentation"] = "\t";
-  (*settings)["enableYAMLCompatibility"] = false;
-  (*settings)["dropNullPlaceholders"] = false;
-  (*settings)["useSpecialFloats"] = false;
-  (*settings)["emitUTF8"] = false;
-  (*settings)["precision"] = 17;
-  (*settings)["precisionType"] = "significant";
+  Json::Value settings;
+  settings["commentStyle"] = "All";
+  settings["indentation"] = "\t";
+  settings["enableYAMLCompatibility"] = false;
+  settings["dropNullPlaceholders"] = false;
+  settings["useSpecialFloats"] = false;
+  settings["emitUTF8"] = false;
+  settings["precision"] = 17;
+  settings["precisionType"] = "significant";
   //! [StreamWriterBuilderDefaults]
+  return settings;
+}());
+
+// static
+void StreamWriterBuilder::setDefaults(Json::Value* settings) {
+  *settings = global_settings_;
+}
+
+// static
+void StreamWriterBuilder::updateDefaults(const Json::Value& settings) {
+  global_settings_ = settings;
 }
 
 String writeString(StreamWriter::Factory const& factory, Value const& root) {