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A sketch written to help people understand the use of references and pointers
/*
* ref_vs_pointers
* A sketch written to help people understand the use of references and pointers
* Written by Peter Dalmaris, April 8 2016.
* Arduino Tips and Tricks
* txplore.com
*
* Requirements: MemoryFree from https://github.com/McNeight/MemoryFree
*/
#include <MemoryFree.h>
void setup() {
// put your setup code here, to run once:
Serial.begin(9600);
print_free_memory();
int a = 5;
int b = 10;
int *pointer; // Create a new pointer. Variable "pointer" will contain a memory address where
// an int value will be stored
print_free_memory();
// Play with pointer to variable a
Serial.println(F("1 ----- a -----"));
Serial.print(F("a="));
Serial.println(a);
pointer = &a; //Get the address for variable "a" and assign it to pointer "pointer"
*pointer = 6; // Store value "6" to memory location stored in "pointer".
Serial.print(F("a="));
Serial.println(a);
print_free_memory();
Serial.println();
// Play with pointer to variable b
Serial.println(F("2 ----- b -----"));
Serial.print(F("b="));
Serial.println(b);
pointer = &b; //Get the address for variable "b" and assign it to pointer "pointer"
// This will reassign the memory location stored in "pointer" from the original
// memory location for int "a", to that of int "b".
*pointer = 11; // Store value "11" to memory location stored in "pointer".
Serial.print(F("b="));
Serial.println(b);
print_free_memory();
Serial.println();
// Play with passing data to a function via reference
pass_reference(a); //Even though we are passign int "a", the function expects a reference as a parameter.
//Notice that the function declaration uses the "&" operator. This will retrieve
//the memory location for int "a" instead of making a copy for it.
pass_reference(b); //Exactly as above.
// Play with passing data to a function via pointer
pass_pointer(pointer);
pointer = &a;
pass_pointer(pointer);
//Play with passing data to a function via value
pass_value(a);
pass_value(b);
//Do all of the above using a String object (instead of primitives)
String a_string = "Hello World!";
String b_string = "Hello again!";
String *string_pointer;
//Print the content of the pointer;
string_pointer = &a_string;
Serial.println(F("6 ------- String a -----"));
Serial.print(F("string a="));
Serial.println(*string_pointer);
print_free_memory();
Serial.println();
string_pointer = &b_string;
Serial.println(F("7 ------- String b -----"));
Serial.print(F("string b="));
Serial.println(*string_pointer);
print_free_memory();
Serial.println();
// Play with passing string to a function via reference
pass_reference_str(a_string);
pass_reference_str(b_string);
// Play with passing string to a function via pointer
// pointer = &a_string;
pass_pointer_str(&a_string);
// pointer = &a_string;
pass_pointer_str(&b_string);
//Play with passing data to a function via value
pass_value_str(a_string);
pass_value_str(b_string);
}
void loop() {
// put your main code here, to run repeatedly:
}
void pass_reference(int &a_ref)
{
Serial.println(F("3 ----- Passing by reference -----"));
Serial.println(a_ref);
print_free_memory();
Serial.println();
}
void pass_pointer(int *a_pointer)
{
Serial.println(F("4 ----- Passing by pointer -----"));
Serial.println(*a_pointer);
print_free_memory();
Serial.println();
}
void pass_value(int value)
{
Serial.println(F("5 ----- Passing by value-----"));
Serial.println(value);
print_free_memory();
Serial.println();
}
void pass_reference_str(String &a_ref)
{
Serial.println(F("8 ----- Passing String by reference -----"));
Serial.println(a_ref);
print_free_memory();
Serial.println();
}
void pass_pointer_str(String *a_pointer)
{
Serial.println(F("9 ----- Passing String by pointer -----"));
Serial.println(*a_pointer);
print_free_memory();
Serial.println();
}
void pass_value_str(String value)
{
Serial.println(F("10 ----- Passing String by value-----"));
Serial.println(value);
print_free_memory();
Serial.println();
}
void print_free_memory(){
Serial.print(F("freeMemory()="));
Serial.println(freeMemory());
}
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