Added support for PROGMEM (issue #76)

CHANGELOG.md

@@ -1,6 +1,11 @@
 ArduinoJson: change log
 =======================
 
+HEAD
+----
+
+* Added support for PROGMEM (issue #76)
+
 v5.7.0
 ------
 

examples/ProgmemExample/ProgmemExample.ino

@@ -0,0 +1,51 @@
+// Copyright Benoit Blanchon 2014-2016
+// MIT License
+//
+// Arduino JSON library
+// https://github.com/bblanchon/ArduinoJson
+// If you like this project, please add a star!
+
+#include <ArduinoJson.h>
+
+// About
+// -----
+// This example shows the different ways you can use PROGMEM with ArduinoJson.
+// Please don't see this as an invitation to use PROGMEM.
+// On the contrary, you should always use char[] when possible, it's much more
+// efficient in term of code size, speed and memory usage.
+
+void setup() {
+#if ARDUINO_ARCH_AVR
+  DynamicJsonBuffer jsonBuffer;
+
+  // You can use a Flash String as your JSON input.
+  // WARNING: the content of the Flash String will be duplicated in the
+  // JsonBuffer.
+  JsonObject& root =
+      jsonBuffer.parseObject(F("{\"sensor\":\"gps\",\"time\":1351824120,"
+                               "\"data\":[48.756080,2.302038]}"));
+
+  // You can use a Flash String to get an element of a JsonObject
+  // No duplication is done.
+  long time = root[F("time")];
+
+  // You can use a Flash String to set an element of a JsonObject
+  // WARNING: the content of the Flash String will be duplicated in the
+  // JsonBuffer.
+  root[F("time")] = time;
+
+  // You can set a Flash String to a JsonObject or JsonArray:
+  // WARNING: the content of the Flash String will be duplicated in the
+  // JsonBuffer.
+  root["sensor"] = F("gps");
+
+#else
+
+#warning PROGMEM is only supported on AVR architecture
+
+#endif
+}
+
+void loop() {
+  // not used in this example
+}

include/ArduinoJson/Configuration.hpp

@@ -27,6 +27,15 @@
 #define ARDUINOJSON_ENABLE_ARDUINO_STRING 1
 #endif
 
+// On AVR archiecture, we can use PROGMEM
+#ifndef ARDUINOJSON_ENABLE_PROGMEM
+#ifdef ARDUINO_ARCH_AVR
+#define ARDUINOJSON_ENABLE_PROGMEM 1
+#else
+#define ARDUINOJSON_ENABLE_PROGMEM 0
+#endif
+#endif
+
 // Arduino doesn't have std::string
 #ifndef ARDUINOJSON_ENABLE_STD_STRING
 #define ARDUINOJSON_ENABLE_STD_STRING 0
@@ -87,6 +96,11 @@
 #define ARDUINOJSON_ENABLE_ARDUINO_STRING 0
 #endif
 
+// PROGMEM is only available on AVR architecture
+#ifndef ARDUINOJSON_ENABLE_PROGMEM
+#define ARDUINOJSON_ENABLE_PROGMEM 0
+#endif
+
 // on a computer, we can assume that the STL is there
 #ifndef ARDUINOJSON_ENABLE_STD_STREAM
 #define ARDUINOJSON_ENABLE_STD_STREAM 1

include/ArduinoJson/Internals/StringFuncs.hpp

@@ -90,5 +90,26 @@ struct StringFuncs<StringSumHelper> : StdStringFuncs<StringSumHelper> {};
 template <>
 struct StringFuncs<std::string> : StdStringFuncs<std::string> {};
 #endif
+
+#if ARDUINOJSON_ENABLE_PROGMEM
+template <>
+struct StringFuncs<const __FlashStringHelper*> {
+  static bool equals(const __FlashStringHelper* str, const char* expected) {
+    return strcmp_P((PGM_P)str, expected) == 0;
+  }
+
+  template <typename Buffer>
+  static char* duplicate(const __FlashStringHelper* str, Buffer* buffer) {
+    if (!str) return NULL;
+    size_t size = strlen_P((PGM_P)str) + 1;
+    void* dup = buffer->alloc(size);
+    if (dup != NULL) memcpy_P(dup, (PGM_P)str, size);
+    return static_cast<char*>(dup);
+  }
+
+  static const bool has_append = false;
+  static const bool should_duplicate = true;
+};
+#endif
 }
 }