I had assumed that the .ino file was just the main .cpp file.

The problem I am having is that when I create a project_name.h file and #include it in project_name.ino, the project will not compile.  I get the following:

Compiling debug version of 'Temp_RH_WiFi_Arduino' for 'Arduino/Genuino Uno'
Temp_RH_WiFi_Arduino.cpp.o:In function `__static_initialization_and_destruction_0
Temp_RH_WiFi_Arduino.ino:~SoftwareSerial()
Temp_RH_WiFi_Arduino.cpp.o:In function `setup
Temp_RH_WiFi_Arduino.ino:begin(long)
Temp_RH_WiFi_Arduino.ino:listen()
Temp_RH_WiFi_Arduino.cpp.o:In function `__static_initialization_and_destruction_0
Temp_RH_WiFi_Arduino.ino:SoftwareSerial(unsigned char, unsigned char, bool)
ESP8266_Functions.cpp.o:In function `ESP8266CmdResponse(char const*, unsigned long, unsigned long, SoftwareSerial&)
ESP8266_Functions.cpp:listen()
collect2.exe*:error: ld returned 1 exit status
Error creating .elf

When I comment out the lines in project_name.h and simply add those lines to the project_name.ino file it does compile.

Any idea why this would be the case?

Thanks for the code

For C++ you need to mark external code as extern

extern  

tips

You can remove all folder paths from libraries. Ensure that all used libraries are included in the .ino so that library paths are resolved for intellisense correctly.

#include <Lib.h>

not

#include <Lib\Lib.h>

You should not create a variable called ESP8266 because it is #defined as part of the tool chain. Your softwareSerial is called that.

avr\ relates to arduino Uno

These are good questions for the Arduino.cc forum. I am no expert with cpp so I stick to supporting the plugin

Interested to hear your findings thanks

thanks