variable or field declared void Error

Question

For a larger sketch, I have separated a chunk of code in a separate .cpp file

#include "msg.h"
#include <Arduino.h>
#include <HTTPClient.h>
#include <ArduinoJson.h>
void parseResponse(String &payload, float &temp, float &wind, int &pressure, int &humid, float &feel, int &uv)
{
 String json = payload;
 // Serial.println(json); // enable to debug
 StaticJsonDocument<128> filter;
 JsonObject filter_current = filter.createNestedObject("current");
 filter_current["temp_c"] = true;
 filter_current["wind_mph"] = true;
 filter_current["pressure_mb"] = true;
 filter_current["precip_in"] = true;
 filter_current["humidity"] = true;
 filter_current["feelslike_c"] = true;
 filter_current["uv"] = true;
 StaticJsonDocument<256> doc;
 // Deseriliaze and display error description if there is any
 DeserializationError error = deserializeJson(doc, json, DeserializationOption::Filter(filter));
 if (error)
 {
 Serial.print("deserializeJson() failed: ");
 Serial.println(error.c_str());
 return;
 }
 JsonObject current = doc["current"];
 temp = current["temp_c"]; // 80
 wind = current["wind_mph"]; // 5.6
 pressure = current["pressure_mb"]; // 1005
 humid = current["humidity"]; // 93
 feel = current["feelslike_c"]; // 6.9
 uv = current["uv"]; // 1
}

together with its header file as below:

#ifndef MSG_H
#define MSG_H
void parseResponse(String &payload, float &temp, float &wind, int &pressure, int &humid, float &feel, int &uv);
#endif

I have included all the relevant libraries in the .cpp files. However, when I try to compile the code I get multiple errors such as

In file included from src/weatherapi.cpp:1:0:
include/weatherapi.h:4:17: error: variable or field 'getRequest' declared void
 void getRequest(String &payload);
 ^
include/weatherapi.h:4:17: error: 'String' was not declared in this scope
include/weatherapi.h:4:25: error: 'payload' was not declared in this scope
 void getRequest(String &payload);
 ^
Archiving .pio\build\lolin32\liba47\libPubSubClient.a
In file included from src/msg.cpp:1:0:
include/msg.h:4:20: error: variable or field 'parseResponse' declared void
 void parseResponse(String &payload, float &temp, float &wind, int &pressure, int &humid, float &feel, int &uv);
 ^
include/msg.h:4:20: error: 'String' was not declared in this scope
include/msg.h:4:28: error: 'payload' was not declared in this scope
 void parseResponse(String &payload, float &temp, float &wind, int &pressure, int &humid, float &feel, int &uv);
 ^
include/msg.h:4:37: error: expected primary-expression before 'float'
 void parseResponse(String &payload, float &temp, float &wind, int &pressure, int &humid, float &feel, int &uv);
 ^
include/msg.h:4:50: error: expected primary-expression before 'float'
 void parseResponse(String &payload, float &temp, float &wind, int &pressure, int &humid, float &feel, int &uv);
 ^
include/msg.h:4:63: error: expected primary-expression before 'int'
 void parseResponse(String &payload, float &temp, float &wind, int &pressure, int &humid, float &feel, int &uv);
 ^
include/msg.h:4:78: error: expected primary-expression before 'int'
 void parseResponse(String &payload, float &temp, float &wind, int &pressure, int &humid, float &feel, int &uv);
 ^
include/msg.h:4:90: error: expected primary-expression before 'float'
 void parseResponse(String &payload, float &temp, float &wind, int &pressure, int &humid, float &feel, int &uv);
 ^
include/msg.h:4:103: error: expected primary-expression before 'int'
 void parseResponse(String &payload, float &temp, float &wind, int &pressure, int &humid, float &feel, int &uv);

The function parseResponse doesn't return anything so I don't know why it's complaining about being declared as void. Same is true for the function getRequest. Also, is there something wrong in the function prototype as I am passing references?

Edit: Here is the weatherapi.cpp & .h file

#include "weatherapi.h"
#include <HTTPClient.h>
#include <Arduino.h>
const char url[] = "http://api.weatherapi.com/v1/current.json?key=xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx";
void getRequest(String &payload)
{
 HTTPClient getClient;
 getClient.begin(url);
 
 int httpCode = getClient.GET();
 //get response and check HTTP status code returned
 if (httpCode > 0)
 {
 payload = getClient.getString();
 Serial.print("HTTP Status: ");
 Serial.println(httpCode);
 }
 else
 {
 Serial.println("Error on HTTP request");
 }
 
 getClient.end();
} 

weatherapi.h file

#ifndef WEATHERAPI_H
#define WEATHERAPI_H
void getRequest(String &payload);
#endif
 

• Majenko: Your problems start before the code you have shown us. Specifically in (or even before) weatherapi.h. It says it doesn't know what String is - did you include Arduino.h in there?
• Zaffresky: Yes I have included Arduino.h but still the same error :(. Please see updated post
• Majenko: Order is important.... Arduno.h must be included before it is used...

Answer 1

In C order is important. Everything is parsed sequentially, and header file inclusions are replaced literally with the header contents at compile time.

Things must be defined before they can be used, and that includes anything that is defined in the Arudino.h header file - that file must be included before anything that uses it - and of course that means that it must come before any headers that use things from Arduino.h

To be safer it's good to include Arduino.h in every file that uses anything from it so you don't run into these problems in future.

• Zaffresky: Included Arduino.h in all .cpp files and it compiles without error. Though I omitted it only in places where I thought it wasn't needed at all but perhaps it was required somewhere.