It has always been the case that you need to place your own prototypes between the creation of a type and where they are first used.
Arduino IDE has moved to using a new system to deduce the location of prototypes which works most of the time. We will shortly move to the same.
The older system places them before first line of real code (non #include), which is why users types would always be placed in .h files. You can override by adding them yourself. Notice I have added prototypes for the save and load methods that make use of the types in their signatures.
Code (C++):// ArduinoJson - arduinojson.org
// Copyright Benoit Blanchon 2014-2019
// MIT License
//
// This example shows how to store your project configuration in a file.
// It uses the SD library but can be easily modified for any other file-system.
//
// The file contains a JSON document with the following content:
// {
// "hostname": "examples.com",
// "port": 2731
// }
//
// https://arduinojson.org/v6/example/config/
#include <ArduinoJson.h>
#include <SD.h>
#include <SPI.h>
// Our configuration structure.
//
// Never use a JsonDocument to store the configuration!
// A JsonDocument is *not* a permanent storage; it's only a temporary storage
// used during the serialization phase. See:
// https://arduinojson.org/v6/faq/why-must-i-create-a-separate-config-object/
struct ConfigObject {
char hostname[64];
int port;
};
////// prototypes in correct location for cpp
//
void saveConfiguration(const char *filename, const Config &config);
void loadConfiguration(const char *filename, Config &config);
//
///////////////////
const char *filename = "/config.txt"; // <- SD library uses 8.3 filenames
ConfigObject config; // <- global configuration object
// Loads the configuration from a file
void loadConfiguration(const char *filename, Config &config) {
// Open file for reading
File file = SD.open(filename);
// Allocate a temporary JsonDocument
// Don't forget to change the capacity to match your requirements.
// Use arduinojson.org/v6/assistant to compute the capacity.
StaticJsonDocument<512> doc;
// Deserialize the JSON document
DeserializationError error = deserializeJson(doc, file);
if (error)
Serial.println(F("Failed to read file, using default configuration"));
// Copy values from the JsonDocument to the Config
config.port = doc["port"] | 2731;
strlcpy(config.hostname, // <- destination
doc["hostname"] | "example.com", // <- source
sizeof(config.hostname)); // <- destination's capacity
// Close the file (Curiously, File's destructor doesn't close the file)
file.close();
}
// Saves the configuration to a file
void saveConfiguration(const char *filename, const Config &config) {
// Delete existing file, otherwise the configuration is appended to the file
SD.remove(filename);
// Open file for writing
File file = SD.open(filename, FILE_WRITE);
if (!file) {
Serial.println(F("Failed to create file"));
return;
}
// Allocate a temporary JsonDocument
// Don't forget to change the capacity to match your requirements.
// Use arduinojson.org/assistant to compute the capacity.
StaticJsonDocument<256> doc;
// Set the values in the document
doc["hostname"] = config.hostname;
doc["port"] = config.port;
// Serialize JSON to file
if (serializeJson(doc, file) == 0) {
Serial.println(F("Failed to write to file"));
}
// Close the file
file.close();
}
// Prints the content of a file to the Serial
void printFile(const char *filename) {
// Open file for reading
File file = SD.open(filename);
if (!file) {
Serial.println(F("Failed to read file"));
return;
}
// Extract each characters by one by one
while (file.available()) {
Serial.print((char)file.read());
}
Serial.println();
// Close the file
file.close();
}
void setup() {
// Initialize serial port
Serial.begin(9600);
while (!Serial) continue;
// Initialize SD library
while (!SD.begin(4)) {
Serial.println(F("Failed to initialize SD library"));
delay(1000);
}
// Should load default config if run for the first time
Serial.println(F("Loading configuration..."));
loadConfiguration(filename, config);
// Create configuration file
Serial.println(F("Saving configuration..."));
saveConfiguration(filename, config);
// Dump config file
Serial.println(F("Print config file..."));
printFile(filename);
}
void loop() {
// not used in this example
}
// See also
// --------
//
// https://arduinojson.org/ contains the documentation for all the functions
// used above. It also includes an FAQ that will help you solve any
// serialization or deserialization problem.
//
// The book "Mastering ArduinoJson" contains a case study of a project that has
// a complex configuration with nested members.
// Contrary to this example, the project in the book uses the SPIFFS filesystem.
// Learn more at https://arduinojson.org/book/
// Use the coupon code TWENTY for a 20% discount ❤❤❤❤❤