Pointers and Manual Memory Allocation

lesson#16/main.d

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+import std.stdio: writeln;
+
+void pointers() {
+	int myVariable = 120;
+	int* myPointer = &myVariable;
+
+	/*
+		Valid pointer declarations:
+			type* name;
+			type * name;
+			type *name;
+	*/
+
+	writeln("Memory address of myVariable:\t", &myVariable);
+	writeln("Value of myPointer:\t\t", myPointer);
+
+	writeln("\nValue of myVariable: ", myVariable);
+	writeln("Value of myVariable accessed through my Pointer: ", *myPointer);
+
+	*myPointer += 5;	// modifies the value of myVariable
+	// myPointer += 5;	// !!! modifies the address myPointer points at by sizeof(int)*5
+
+	writeln("\n| *myPointer += 5 |\t => myVariable: ", myVariable);
+
+	myPointer = null;
+
+	/*
+
+	// increments the value of a copy
+	void increment(int num) {
+		num += 1;				
+	}
+
+	// increments the actual value of the variable
+	void increment(ref int num) {
+		num += 1;
+	}
+	
+	// increments the actual value of the variable
+	void increment(int* num) {
+		*num += 1;
+		// num += 1; 	// modifying the address
+	}
+
+	*/
+}
+
+
+void gc_allocations() /*  @nogc  */{
+	import core.memory: GC;
+
+	/**** GC basics ****/
+	// disabling GC collection cycles | it does not gurantee, that GC cycles won't be run
+	// GC cycle will be run anyway, if more memory is required
+	GC.disable(); 
+
+	// enabling GC collection cycles
+	GC.enable();
+
+	// explicitly starting a GC collection cycle
+	GC.collect();
+
+
+	int* var1 = new int; 		// allocating an int on GC heap
+	int[] var2 = new int[42];	// allocating a dynamic array of 42 ints on GC heap
+	var2 ~= 2;
+
+	// allocating a fixed size array on the GC heap
+	//int* var3 = cast(int*)GC.malloc(int.sizeof * 42);
+	//int* var3 = cast(int*)GC.realloc(null, int.sizeof * 42);
+	int* var3 = cast(int*)GC.calloc(int.sizeof * 42);
+
+	GC.free(var3);
+}
+
+void stdc_allocations() {
+	import core.stdc.stdlib: malloc, free; // malloc, realloc, etc... from C stdlib
+	import core.memory: GC;
+
+	int size = 42;
+
+	// allocating memory the C-way
+	int* var = cast(int*)malloc(int.sizeof * size);
+
+	// (*) optional: adding var to GC memory
+	GC.addRange(var, size);
+
+	// ...........
+
+	// if (*), then var should be removed before freeing 
+	GC.removeRange(var);
+
+	// freeing var
+	free(var);
+}
+
+void main() {
+	pointers();
+	gc_allocations();
+	stdc_allocations();
+}
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