How to pass a sketch instance to a library ?

Using Arduino Programming Questions
#1

Hi,

I would like to use a instance defined in a sketch in a library.
Attached the sketch and library

The following is the simple test that is not working

  1. In a sketch I (Test.ino):
    #include <Testlib.h>

and the definition of:
EthernetClient client;

In the library (Testlib.cpp) I use a function such as:
void clientWrite ()
{
client.write(“Hello”);
}

Compilation gives error such:
…/Testlib/Testlib.cpp: In function ‘void clientWrite()’:
…/Testlib/Testlib.cpp:5:3: error: ‘client’ was not declared in this scope
client.write(“Hello”);
^
Error compiling.

  1. If I define the client in the library Testlib.h and not in the Test.ino sketch
    #ifndef Testlib_H
    #define Testlib_H
    #include <Arduino.h>
    #include <Ethernet.h>
    EthernetClient client;
    void clientWrite();
    #endif

Compilation gives error such:
/var/folders/bq/1_7b3x851wj3d2wxhqqntcnr0000gp/T/build5671766976262198974.tmp/Testlib/Testlib.cpp.o:(.bss.client+0x0): multiple definition of `client’
/var/folders/bq/1_7b3x851wj3d2wxhqqntcnr0000gp/T/build5671766976262198974.tmp/Test.cpp.o:/Applications/Test.ino:21: first defined here
collect2: error: ld returned 1 exit status
Error compiling.

  1. If I define the client in the library Testlib.cpp and not in the Test.ino sketch
    #include <Testlib.h>
    EthernetClient client;
    void clientWrite ()
    {
    client.write(“Hello”);
    }
    Compilation gives error such:
    /var/folders/bq/1_7b3x851wj3d2wxhqqntcnr0000gp/T/build5671766976262198974.tmp/Test.cpp.o
    Test.ino: In function ‘void loop()’:
    Test.ino:22:2: error: ‘client’ was not declared in this scope
    Error compiling.

  2. if I defined in the sketch and in the lib ray (.cpp or .h)

/var/folders/bq/1_7b3x851wj3d2wxhqqntcnr0000gp/T/build5671766976262198974.tmp/Testlib/Testlib.cpp.o:(.bss.client+0x0): multiple definition of `client’
/var/folders/bq/1_7b3x851wj3d2wxhqqntcnr0000gp/T/build5671766976262198974.tmp/Test.cpp.o:/Applications/Test.ino:21: first defined here
collect2: error: ld returned 1 exit status
Error compiling.

or

/var/folders/bq/1_7b3x851wj3d2wxhqqntcnr0000gp/T/build5671766976262198974.tmp/Test.cpp.o
Test.ino:13:16: error: redefinition of ‘EthernetClient client’
In file included from Test.ino:2:0:
…/Testlib/Testlib.h:5:16: error: ‘EthernetClient client’ previously declared here
EthernetClient client;
^
Error compiling.

What am I doing wrong and/or is there a solution ??

Thanks in advance
Robert

Testlib.h (110 Bytes)

Testlib.cpp (93 Bytes)

Test.ino (523 Bytes)

#2

Do you need to pass an actual object instance, or will a method pointer do?
There are examples of libraries, like pin change interrupt and scheduler that accept function pointers to user callbacks.

#3

If all you need is to pass the object so you can use the stream features (read/write) then you can do something like this:

void clientWrite( Stream &client )
{
** client.write("Hello");**
}

This works as Stream is a base class for EthernetClient

If you need the complete object to work with, you can pass a reference to it also:

void clientWrite( EthernetClient &client )
{
** client.write("Hello");**
}

Both these examples allow you to 'pass' the 'client' defined in your sketch, rather than redefining it in the library like you had.
clientWrite( client ); //in sketch

You will have to include Arduino.h & Ethernet.h into your library too.

#4

Formidable !!!

Thanks pYro_65 for your illuminate answer

Robert

#5