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pointers.cpp
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Sat, Aug 24, 02:21

pointers.cpp
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#include <cassert>
#include <cmath>
#include <cstdlib>
#include <iostream>
//////////////////////////////////////////////////////////////////////
void two_variables() {
int x = 1;
int y = 2;
std::cout << &x << "\n";
}
//////////////////////////////////////////////////////////////////////
void get_address() {
int total_sum = 10;
std::cout << &total_sum << "\n";
}
//////////////////////////////////////////////////////////////////////
void pointers_declaration() {
int *p_x;
std::cout << p_x << std::endl;
}
//////////////////////////////////////////////////////////////////////
void pointer_usage_example() {
// x stores an int precision number
int x = 3;
// p_x stores the address of an int
int *p_x = &x;
std::cout << p_x << std::endl;
}
//////////////////////////////////////////////////////////////////////
void char_array_and_pointers() {
char name[250] = "yopla";
char *ptr = name;
}
//////////////////////////////////////////////////////////////////////
void dereferencing() {
int y = 3;
int *p_x = &y;
std::cout << "y = " << y << "\n";
// This changes the value of y
*p_x = 1;
std::cout << "y = " << y << "\n";
}
//////////////////////////////////////////////////////////////////////
void two_variables_question() {
int x = 1;
int y = 2;
*(&y + 1) = 3;
std::cout << &x << "\n";
}
//////////////////////////////////////////////////////////////////////
void unallocated_memory_access() {
// p_x stores the address of a int
// not yet specified
int *p_x;
// trying to assign 1.0 in an unspecified
// memory location
*p_x = 1;
}
//////////////////////////////////////////////////////////////////////
void dynamic_allocation() {
int *x = new int;
*x = 10;
delete x;
}
//////////////////////////////////////////////////////////////////////
void dynamic_allocation_array() {
double *x = new double[10];
double *y = new double[10];
for (int i = 0; i < 10; i++) {
x[i] = double(i);
y[i] = 2.0 * x[i];
}
delete[] x;
delete[] y;
}
//////////////////////////////////////////////////////////////////////
void matrix_allocation() {
int rows = 5, cols = 3;
double **A = new double *[rows];
for (int i = 0; i < rows; i++) {
A[i] = new double[cols];
}
// you can access the values of the array with
A[2][4] = 5;
// At the end: deallocate the memory
for (int i = 0; i < rows; i++) {
delete[] A[i];
}
delete[] A;
}
//////////////////////////////////////////////////////////////////////
void row_major_allocation() {
int rows = 5, cols = 3;
// creates a contiguous memory space
double *p_a = new double[rows * cols];
double **A = new double *[rows];
for (int i = 0; i < rows; i++) {
A[i] = &p_a[i * rows];
A[i] = p_a + i * rows;
}
// you can access the values of the array with
A[2][4] = 5;
// or with
p_a[2 * rows + 4] = 5;
// At the end: de-allocate the memory
delete[] A;
delete[] p_a;
}
//////////////////////////////////////////////////////////////////////
void safe_alloc() {
int *p_x = new int;
assert(p_x != NULL);
}
//////////////////////////////////////////////////////////////////////
int main(int argc, char **argv) {
two_variables();
get_address();
pointers_declaration();
pointer_usage_example();
char_array_and_pointers();
dereferencing();
two_variables_question();
unallocated_memory_access();
dynamic_allocation();
dynamic_allocation_array();
matrix_allocation();
row_major_allocation();
safe_alloc();
}

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