Pointer Variables. Pointers, Structures and Arrays. Schematics Example. Pointer Schematics

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1 Poers, Structures and Arras ; foat ; = ; = 3.8; cout << << end; cout << << end; * ; foat* ; = &; = &; * = 3; * =.2; Poer Variabes 00000AB18 Reference operator get the address of cout << * << end; cout << * << end; Dereference operator go to the address in memor addresses 00000AB AB AB AB0c 00000AB AB14 memor contents AB AB04 X = ; X = ; ECE 244 Programming Fundamentas 1 Coright Tarek S. Abderahman ECE 244 Programming Fundamentas 2 Coright Tarek S. Abderahman Poer Schematics Schematics Eampe memor addresses 00000AB AB AB AB0c 00000AB AB AB AB AB04 * foat* foat 3.8 The arrows indicate the pos-to reation Avoid using/knowing addresses ; foat ; = ; = 3.8; * ; foat* ; = &; = &; * = 3; * =.2; * pz; pz = &; * 3 * pz foat foat* Can two poers po to the same variabe? Can one poer po to two variabes at the same time? ECE 244 Programming Fundamentas 3 Coright Tarek S. Abderahman ECE 244 Programming Fundamentas 4 Coright Tarek S. Abderahman

2 More Use of Poers Structures in C/C++ The above usage of poers is not the most eresting We common use poers to create new variabes whie a program is eecuting, i.e., at run-time = 8; * = &; cout << * << end; = new ; * 8 Reca what a struct in C a coection of variabes of possib different tpes under one name ID; foat vaue; ; struct node first_node; ID foat vaue first_node * = ; cout << * << end; = new ; * = 6; cout << * << end; deete ; = NULL; How to change this to 7? Memor Leak!! 6 struct node second_node; first_node.id = 1; first_node.vaue = 3.8; second_node.id = 2; second_node.vaue =.2; foat second_node ID vaue Fied Access Operator ECE 244 Programming Fundamentas Coright Tarek S. Abderahman ECE 244 Programming Fundamentas 6 Coright Tarek S. Abderahman (*ptr).id = 2; (*ptr).vaue = 6.2; struct node* pptr; pptr = ptr; (*ptr).id = 3; (*ptr).vaue = 8.1; deete ptr; deete pptr; p Poers to structs Draw Schematic (*ptr).id = 2; (*ptr).vaue = 6.2; struct node* pptr; pptr = ptr; (*ptr).id = 3; (*ptr).vaue = 8.1; deete ptr; deete pptr; p Poers to structs ptr->id = 2; ptr->vaue = 6.2; ptr->id = 3; ptr->vaue = 8.1; ECE 244 Programming Fundamentas 7 Coright Tarek S. Abderahman ECE 244 Programming Fundamentas 8 Coright Tarek S. Abderahman

3 Poers in structs Poers in structs ID; struct node* net; ; struct node* ID net ID; struct node* net; ; struct node* ID net #incude <iostream> main() { struct node* head; #incude <iostream> main() { struct node* head; head = new struct node; (*head).id = 0; (*head).net = NULL; head = new struct node; head->id = 0; head->net = NULL; (*ptr).id = 1; (*ptr).net = NULL; ptr->id = 1; ptr->net = NULL; (*head).net = ptr; head->net = ptr; ECE 244 Programming Fundamentas 9 Coright Tarek S. Abderahman ECE 244 Programming Fundamentas 10 Coright Tarek S. Abderahman Poers in structs More Poers struct node* struct node* struct node* 0 1 head ID net ID net Change the ID fied of the second node to 2 #incude <iostream> main() { ** p2p; * p; * q; p = new ; *p = ; Using ptr, aocate a new node; set ID to 3 and net to NULL p2p = &p; q = *p2p; *q = 8; Have the net fied of the second node po to the new node cout << **p2p; ECE 244 Programming Fundamentas 11 Coright Tarek S. Abderahman ECE 244 Programming Fundamentas 12 Coright Tarek S. Abderahman

4 a[4]; a[0] = 4; cout << a[3]; Arras a The size of the arra (number of eements) must be a compie-time known constant #define size 10 a[size]; Arras and Poers Arras and poers enjo a specia reationship the name of the arra can be used as a poer to the first eement of the arra Thus, a[4]; a[0] is the same as *a a[1] is the same as *(a+1) a size; a[size]; X a[i] is the same as *(a+i) Note a+1 does not add 1 to a; it adds 4 ECE 244 Programming Fundamentas 13 Coright Tarek S. Abderahman ECE 244 Programming Fundamentas 14 Coright Tarek S. Abderahman Dnamic Aocation of Arras Dnamic De-Aocation of Arras This specia reationship can use used to aocate arras at run time with on run-time known sizes Once the arra is no onger needed, it can be de-aocated with deete, as for reguar variabes, with a sight difference in snta #incude <iostream> main() { #incude <iostream> main() { * marra; size; * marra; size; marra = new [size]; marra = new [size]; marra[0] = 0; for ( i=1; i < size; ++i) marra[i] = 1; marra[0] = 0; for ( i=1; i < size; ++i) marra[i] = 1; deete [] marra; marra = NULL; ECE 244 Programming Fundamentas 1 Coright Tarek S. Abderahman ECE 244 Programming Fundamentas 16 Coright Tarek S. Abderahman

5 Arras of structs Arras of structs How do we aocate an arra caed a of 4 struct node s? ID; struct node* net; ; How do we aocate an arra caed a of size struct node s, where size is read from cin? struct node a[4]; struct node* a; a = new struct node [size]; How do we deete the dnamica aocated arra? deete [] a; a = NULL; ECE 244 Programming Fundamentas 17 Coright Tarek S. Abderahman ECE 244 Programming Fundamentas 18 Coright Tarek S. Abderahman Arras of Poers Arras of Poers How do we aocate an arra caed a of 100 poers (to ) * a[100]; How do we aocate an arra caed a of 100 poers (to struct nodes) How do we aocate an arra caed a of size poers (to ), where size is read from cin? ** a; a = new *[size]; How do we make each poer in the arra po to an? struct node* a[100]; How do we aocate an arra caed a of size poers (to struct nodes), where size is read from cin? structnode** a; a = new struct node*[size]; for (i=0; i < size; ++i) a[i] = new ; How do we deete the dnamica aocated data? How do we deete the dnamica aocated arra? for (i=0; i < size; ++i) {deete a[i]; a[i] = NULL; deete [] a; a = NULL; deete [] a; a = NULL; ECE 244 Programming Fundamentas 19 Coright Tarek S. Abderahman ECE 244 Programming Fundamentas 20 Coright Tarek S. Abderahman

6 Given structnode** a; a = new struct node*[size]; Arras of Poers How do we get each poer in the arra to po to a dnamica aocated struct node? for (i=0; i < size; ++i) a[i] = new struct node; How do we set a sequence number (from 0 to size-1) for the ID fied of each dnamica aocated struct node? ECE 244 Programming Fundamentas 21 Coright Tarek S. Abderahman