ArduinoJson: API Reference

ARDUINOJSON_ENABLE_PROGMEM

Enables the support of strings stored in program memory, ie in Flash.

The default is 1 of PROGMEM is defined, 0 otherwise.

How to force the value?

If you need to force the support of PROGMEM strings, add this at the top of your program:

#define ARDUINOJSON_ENABLE_PROGMEM 1
#include <ArduinoJson.h>

On the other hand, if you need to disable PROGMEM string, do:

#define ARDUINOJSON_ENABLE_PROGMEM 0
#include <ArduinoJson.h>

This is useful if your platform defines PROGMEM but doesn’t actually support Flash-stored strings.

Where a PROGMEM string can be used?

Once enabled, you can use a PROGMEM string in many places.

  1. You can use a PROGMEM string as your JSON input

     // WARNING: the content of the PROGMEM string will be duplicated in the JsonBuffer.
     JsonObject& root = jsonBuffer.parseObject(F("{\"sensor\":\"gps\",\"time\":1351824120,"
                                "\"data\":[48.756080,2.302038]}"));
    
  2. You can use a PROGMEM string to get an element of a JsonObject

     long time = root[F("time")];
    
  3. You can use a PROGMEM string to set an element of a JsonObject

     // WARNING: the content of the PROGMEM string will be duplicated in the JsonBuffer.
     root[F("time")] = time;
    
  4. You can set a JsonObject (or JsonArray) element to a PROGMEM string:

     // WARNING: the content of the PROGMEM string will be duplicated in the JsonBuffer.
     root["sensor"] = F("gps");
    
  5. You can compare the content of a JsonObject with a PROGMEM string

     if (root["sensor"] == F("gps")) {
         // ...
     }
    
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