Can't compile my library because "String does not name a type"

Question

I am writing a small library to move some code out of the arduino sketch and make it reusable. Problem is that it does not compile since "String does not name a type".

This is my code (reduced):

myESP.h:

#ifndef MYESP_H
#define MYESP_H
#include "Arduino.h"
#include <String>
#include <ESP8266WiFi.h>
#include <ESP8266WiFiMulti.h>
#include <WiFiClient.h>
#include <WiFiClientSecure.h>
#include <WiFiServer.h>
#include <WiFiUdp.h>
 
class myESP {
 private:
 const char* _ssid;
 const char* _password;
 const char* _host;
 public:
 myESP();
 myESP(char * ssid, char * pwd, char * host);
 String macToStr(const uint8_t* mac);
 String doGet(String data, String sensor, int duration);
};
#endif

myESP.cpp:

#include <String>
#include "Arduino.h"
#include "myESP.h"
myESP::myESP() {}
myESP::myESP(char * ssid, char * pwd, char * host) {
 _host = host;
 _password = pwd;
 _ssid = ssid;
}
myESP::String macToStr(const uint8_t* mac) {
}
myESP::String doGet(String data, String sensor, int duration) {
}

When i try to compile it, I get the following:

/Users/lbedogni/Documents/Arduino/libraries/myESP/myESP.cpp:14:1: error: 'String' in 'class myESP' does not name a type myESP::String macToStr(const uint8_t* mac) {

/Users/lbedogni/Documents/Arduino/libraries/myESP/myESP.cpp:22:1: error: 'String' in 'class myESP' does not name a type myESP::String doGet(String data, String sensor, int duration) {

I have tried to change the order of the imports, change libraries, but still it does not compile.

Any idea?

• Nick Gammon: #include <String> - the IDE automatically includes the String type so you don't need this include.

Answer 1

Your syntax is wrong in myESP.cpp. Change this:

myESP::String macToStr(const uint8_t* mac) {
}
myESP::String doGet(String data, String sensor, int duration) {
}

to this:

String myESP::macToStr(const uint8_t* mac) {
}
String myESP::doGet(String data, String sensor, int duration) {
}

The return type is String and the function implementation should be prefixed with the class name myESP::. Obviously, you also need to fill in the body of the implementation or you'll get more errors because you don't actually return anything.