Displaying Text from Datalogger shield on OLED SSD1315 (arduino-seeds)?

Projects Programming
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first of all: a "macro" is something very different than any C++-language detail

using the #define "statement" to make the compiler "write" code

#define can be used to make the compiler replace text that describes something with (almost) anything else
easy example
let's assume IO-pin number 4 shall be set to work as output
the command for defining an IO-pin to be configured as output is

pinMode(4,OUTPUT);
the number "4" says nothing about he purpose of this IO-pin

let's assume the IO-pin shall switch On/Off a buzzer

you would have to add a comment to explain
pinMode(4,OUTPUT); // IO-pin 4 is buzzer

the compiler needs the number. To make the code easier to read and understand
#define BuzzerPin 4
So the command looks like this
pinMode(BuzzerPin,OUTPUT);

the descriptive word "BuzzerPin" gets replaced through the compiler by a "4"
so what the compiler compiles is still 'pinMode(4,OUTPUT);'

This means - in some way - the define changes your source-code-file right before compiling

 pinMode(BuzzerPin,OUTPUT);

gets replaced by

 pinMode(4,OUTPUT);

the #define can do much more than just replace a word by a single number
it can even take parameters like in this example

#define dbg(myFixedText, variableName) \
  Serial.print( F(#myFixedText " "  #variableName"=") ); \
  Serial.println(variableName);
// usage: dbg("1:my fixed text",myVariable);
// myVariable can be any variable or expression that is defined in scope

here myFixedText and variableName are "variables" on the macro-level

if you write this line

dbg("Hello",Counter);

and you start compiling there will happen two steps
inside the define

#define dbg(myFixedText, variableName)
Serial.print( F(#myFixedText " " #variableName"=") );
Serial.println(variableName);

the macro-variable myFixedText is "evaluated to "Hello"
the macro-variable variableName is evaluated to Counter

which means as a first step what happends is

#define dbg("Hello", Counter)

and a second step replace #define dbg("Hello", Counter) by

Serial.print( F("Hello" " " Counter"=") );
Serial.println(Counter);

It will be enough if you understand the pattern

writing

somewhere in your code you defined a variable

int Counter = 123;

somewhere else in your code you write

dbg("Hello",Counter);

results in serial output
"Hello" Counter=123

writing

somewhere in your code you defined a variable

char myArrayOfChar [ ] = "This is my message";

and somewhere else in your code

dbg("Test",myArrayOfChar);

results in serial output
"Test" myArrayOfChar=This is my message

writing

somewhere in your code you defined a variable

byte numberOfButtonPresses = 678;

and somewhere else in your code

dbg("function myTestfunc",numberOfButtonPresses);

results in serial output
"function myTestfunc" numberOfButtonPresses=678

So dbg and dbgi work this way
first parameter a fixed text that is just quoted
second parameter a variable-name or an expression where the macro prints to the serial monitor the variable-name a "=" and then the value of the variable

best regards Stefan

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