Scope of variables in C++ - c++

Question

for the sake of overview, I wanted to outsource a few functions in another file.
Therefore I created a corresponding cpp and h file and put the funtions in there:
#include <routines.h>
void splash()
{
oled.startScreen();
oled.clear();
oled.drawImage(start_logo, 0, 0, 128, 8);
}
void prepareDisplay(){
unsigned int i,k;
unsigned char ch[5];
oled.clear();
oled.startScreen();
oled.cursorTo(0,0);
oled.printString( "ATTiny");
}
Problem is that those functions use variables (oled, start_logo) from the main file which leads to them being out of scope.
Main.cpp file:
#include <Arduino.h>
#include "SSD1306_minimal.h"
#include <EEPROM.h>
#include <routines.h>
//eeprom adresses:
byte calibratedAddress = 0;
//global variables:
bool isCalibrated;
//pin definitions:
const byte led = PA5;
SSD1306_Mini oled;
const unsigned char start_logo [] PROGMEM = {
0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00 ongoing...
};
void setup(){
oled.init(0x3c);
oled.clear();
delay(1000);
splash();
delay(8000);
oled.clear();
}
void loop() {
}
Is it somehow possible to "hand over" the variables to the outsourced functions and if yes, how?
Thanks in advance for your help!

Answer 1

There's many ways to approach this. One easy way is to pass the needed varaible as an argument into the functions that need it.
// Pass the values needed as arguments
void splash(byte oled, unsigned char* start_logo)
{
oled.startScreen();
oled.clear();
oled.drawImage(start_logo, 0, 0, 128, 8);
}
Another way is to keep the functions as is and declare the variables in the new cpp file
// extern says that this variable is not defined .cpp file
// It's defined in another file
extern SSD1306_Mini oled;
// static in this context makes this variable only visible to this .cpp file
// extern in another file can't get this
static const unsigned char start_logo[] = {
0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00 // more
};
void splash()
{
oled.startScreen();
oled.clear();
oled.drawImage(start_logo, 0, 0, 128, 8);
}
void prepareDisplay(){
unsigned int i,k;
unsigned char ch[5];
oled.clear();
oled.startScreen();
oled.cursorTo(0,0);
oled.printString( "ATTiny");
}