Jim Gilbey

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8 years, 7 months ago.

Compiler error using pc.printf function in a class method - definition error somewhere?

I declare an instance of the serial class in main:-

Serial pc(USBTX, USBRX);

Then in library SerialCommand.cpp, in the addCommand method, I output data over the serial port using pc if SERIALCOMMAND_DEBUG is defined (which in this case it is):

void SerialCommand::addCommand(const char *command, void (*function)()) {
  #ifdef SERIALCOMMAND_DEBUG
    pc.printf("Adding command (");
    pc.printf(commandCount);
    pc.printf("): ");
    pc.println(command);
  #endif

This generates the followinging error from the compiler:

Error: Identifier "pc" is undefined in "mSerialCommand/mSerialCommand.cpp", Line: 50, Col: 6

pc has been defined in main, but can't be found by addCommand....how do I make pc visible to addCommand?

I feel that this must be something very basic, but can't seem to reference my intial definition of pc. Any thoughts? Jimgi

1 Answer

Andy A
8 years, 7 months ago.

You tell the compiler that it is defined external to that file by adding a line to mSerialCommand.cpp:

extern Serial pc;

That will tell the compiler that a serial port called pc is defined as a global elsewhere.

The compiler treats each .cpp file as a completely independent entity that knows nothing about the contents of other .cpp files.

If you want to use the same globals in multiple files it's normal to put the extern lines into a .h header file that you can then include in everything, that way all of the globals are listed in one place and there is no danger of getting different spellings in different files etc...

thanks Andy, I did this, and it doesn't seem to understand Serial: Error: Identifier "Serial" is undefined in "mSerialCommand/mSerialCommand.cpp", Line: 26, Col: 11

#include "mSerialCommand.h"
  extern Serial pc;
/**
 * Constructor makes sure some things are set.
 */
SerialCommand::SerialCommand()
  : commandList(NULL),
    commandCount(0),
posted by Jim Gilbey 15 Sep 2015

You also need to include mbed.h otherwise it doesn't know what a Serial is.

Both the mbed include and the extern could go in mSerialCommand.h instead if you wanted

posted by Andy A 15 Sep 2015

Yup! That did it - thanks for the help Andy. I assumed that because main.cpp included the mbed.h file, that it was enough!

The library is a re-write of the Arduino SerialCommand library for the mbed. Pretty much works now - this was just the last bit to include the debug switch. I gave up on the RPC library.... Jimgi

posted by Jim Gilbey 15 Sep 2015

You can also just use printf without the pc part, then you also don't need to use the extern part.

posted by Erik - 15 Sep 2015

Yes, that works, but presumably I can control the Serial pc(USBTX, USBRX) parameters such as baud-rate with the pc approach?

posted by Jim Gilbey 15 Sep 2015

Yes, however if you set the baud rate with pc, then normal printf will use the same baud rate since it is the same hardware.

posted by Erik - 15 Sep 2015