C++ Structs

C. Papachristos

Robotic Workers Lab

University of Nevada, Reno

CS-202

Course Week

CS-202 C. Papachristos

Course , Projects , Labs:

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Your 2^nd Project will be announced today Thursday 1/30.

1^st Project Deadline was this Wednesday 1/29.

• NO Project accepted past the 24-hrs delayed extension (@ 20% grade penalty).
• Send what you have in time!

Today’s Topics

CS-202 C. Papachristos

C++ Structs

• C (basic) Structs
• C++ Context
• Struct vs Class

​

Structs and Arrays

Structs and Functions

C++ Structs

CS-202 C. Papachristos

Description

A “Structure” is a collection of related data items, possibly of different types.

• A structure type in C++ is called struct.

​

A struct is heterogeneous:

• It can be composed of data of different types.

An array is homogeneous:

• It can contain only data of the same type.

vs

C++ Structs

CS-202 C. Papachristos

Description

A “Structure” is a collection of related data items, possibly of different types.

A struct is heterogeneous in that it can be composed of data of different types.

​

​

​

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In contrast, an array is homogeneous since it can contain only data of the same type.

C++ Structs

CS-202 C. Papachristos

Description

Structures are used to hold data that belong together.

Examples:

• Student record: student id, name, major, gender, start year, …

• Bank account: account number, name, currency, balance, …

• Address book contact: name, address, telephone number, …

​

In database applications, structures are called records.

C++ Structs

CS-202 C. Papachristos

Members

Struct Members (or Fields):

• Individual components of a struct type.

Versatility:

Struct Members can be of different types:

• Simple
• Array
• Another struct

C++ Structs

CS-202 C. Papachristos

Members

Naming – Resolution:

• A struct is named as a whole.
• Individual Struct Members are named using field identifiers.

​

Versatility:

Complex data structures can be formed by defining arrays of structs.

C++ Structs

CS-202 C. Papachristos

Type Declaration

struct <struct-type> {

<type> <identifier_list>;

<type> <identifier_list>;

...

} ;

Example:

struct Date {

int day;

int month;

int year;

} ;

struct Date {

int day, month, year;

int hours, minutes, seconds;

long microseconds;

} ;

or

• Members in Brackets
• Semicolon

• Type Name is up to you to declare!

C++ Structs

CS-202 C. Papachristos

Type Declaration

Examples:

struct StudentInfo {

int id;

int age;

char gender;

double gpa;

};

​

struct StudentGrade {

char name[9];

char course[9];

int lab[5];

int homework[3];

int exam[2];

};

​

The StudentInfo structure has 4 members of different types.

The StudentGrade structure has 5 members of different array types.

C++ Structs

CS-202 C. Papachristos

Type Declaration

Examples:

struct BankAccount {

char name[15];

int acountNo[10];

double balance;

Date birthday;

};

​

​

struct StudentRecord {

char name[9];

int id;

char dept[4];

char gender;

};

​

The BankAccount structure has simple, array and struct types as members.

The StudentRecord structure has 4 members.

C++ Structs

CS-202 C. Papachristos

Variable Declaration

Declaration of a variable of struct type:

• NOTE: Type declaration must come first.

struct <struct-type> {

<type> <identifier_list>;

...

} ;

Declaration of a new variable of that type:

<struct-type> <identifier_list>;

Example:

StudentRecord student1, student2;

struct StudentRecord {

char name[9];

int id;

char dept[4];

char gender;

};

C++ Structs

CS-202 C. Papachristos

Variable Declaration

Example:

StudentRecord student1, student2;

​

• Both variables of type:

(struct)StudentRecord

struct StudentRecord {

char name[9];

int id;

char dept[4];

char gender;

};

C++ Structs

CS-202 C. Papachristos

Member Access

The Dot (.) Pointer-to-Member Operator:

Used to provide struct type member access.

<struct-variable>.<member_name>;

​

Example:

student1 . name

student1 . id

student1 . dept

student1 . gender

​

struct StudentRecord {

char name[9];

int id;

char dept[4];

char gender;

};

Member Access

Example:

strcpy(student1.name, "John Doe");� student1.id = 123;� strcpy(student1.dept, "CSE");� student1.gender = 'M';� cout << "The student is ";� switch (student1.gender){� case 'F': cout << "Ms. "; break;� case 'M': cout << "Mr. "; break;� }� cout << student1.name << endl;

​

C++ Structs

CS-202 C. Papachristos

Member Access

Example:

strcpy(student1.name, "John Doe");� student1.id = 123;� strcpy(student1.dept, "CSE");� student1.gender = 'M';� cout << "The student is ";� switch (student1.gender){� case 'F': cout << "Ms. "; break;� case 'M': cout << "Mr. "; break;� }� cout << student1.name << endl;

​

C++ Structs

CS-202 C. Papachristos

Member Access

Example:

strcpy(student1.name, "John Doe");� student1.id = 123;� strcpy(student1.dept, "CSE");� student1.gender = 'M';� cout << "The student is ";� switch (student1.gender){� case 'F': cout << "Ms. "; break;� case 'M': cout << "Mr. "; break;� }� cout << student1.name << endl;

​

C++ Structs

CS-202 C. Papachristos

Member Access

Example:

strcpy(student1.name, "John Doe");� student1.id = 123;� strcpy(student1.dept, "CSE");� student1.gender = 'M';� cout << "The student is ";� switch (student1.gender){� case 'F': cout << "Ms. "; break;� case 'M': cout << "Mr. "; break;� }� cout << student1.name << endl;

​

C++ Structs

CS-202 C. Papachristos

Member Access

Example:

strcpy(student1.name, "John Doe");� student1.id = 123;� strcpy(student1.dept, "CSE");� student1.gender = 'M';� cout << "The student is ";� switch (student1.gender){� case 'F': cout << "Ms. "; break;� case 'M': cout << "Mr. "; break;� }� cout << student1.name << endl;

​

C++ Structs

CS-202 C. Papachristos

Member Access

Example:

strcpy(student1.name, "John Doe");� student1.id = 123;� strcpy(student1.dept, "CSE");� student1.gender = 'M';� cout << "The student is ";� switch (student1.gender){� case 'F': cout << "Ms. "; break;� case 'M': cout << "Mr. "; break;� }� cout << student1.name << endl;

​

C++ Structs

CS-202 C. Papachristos

Output:

The student is Mr. John Doe

​

C++ Structs

CS-202 C. Papachristos

Initialization

StudentRecord student1 = {"John Doe", 123, "CSE", 'M'};

• Heavily depends on struct type definition.

Compromised maintainability.

• Might break (type mismatch).
• Might work but mess up (wrong value assignment).

​

struct StudentRecord{

char name[9];

int id;

char dept[4];

char gender;

};

C++ Structs

CS-202 C. Papachristos

Initialization

StudentRecord student1 = {"John Doe", 123, "CSE", 'M'};

• Heavily depends on struct type definition.

Compromised maintainability.

• Might break (type mismatch).
• Might work but mess up (wrong value assignment).

​

Attention! No C99 Inline initialization list with designators (NOT supported in C++):

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StudentRecord student1 = {.name="John Doe",.Id=123,.dept="CSE",.gender='M'};

StudentRecord student1 = {.name="John Doe",123,"CSE",'M'};

​

StudentRecord student1 = {.dept="CSE",‘M’,.name="John Doe",.id=123};

​

(Note: C++20 reintroduces the concept, under stricter rules …)

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struct StudentRecord{

char name[9];

int id;

char dept[4];

char gender;

};

C++ Structs

CS-202 C. Papachristos

Initialization

StudentRecord student1 = {"John Doe", 123, "CSE", 'M'};

• Heavily depends on struct type definition.

Compromised maintainability.

• Might break (type mismatch).
• Might work but mess up (wrong value assignment� altogether or wrong semantics).

​

• Too reliant on many “semantics”…

struct StudentRecord{

char name[9];

int id;

char dept[4];

char gender;

};

struct StudentRecord{

char name[5];

int id;

char dept[3];

char gender;

};

Potential Problems due to change in struct declaration!

• C++ static array type-checking by their size yields compile-time error: initializer-string for array of chars is too long [-fpermissive]
• In C allocated array memory bounds may be overwritten …

C++ Structs

CS-202 C. Papachristos

Assignment

The values contained in one struct type variable can be assigned to another variable of the same struct type.

• This involves Data Copy operations.

​

Example:

strcpy(student1.name, "John Doe");� student1.id = 123;� strcpy(student1.dept, "CSE");� student1.gender = 'M';�� StudentRecord student2 = student1;

C++ Structs

CS-202 C. Papachristos

Nested Structures

A struct type can be a member of another struct.

• Program design w.r.t. inherent attributes.

​

Example:

struct Point { � double x, y;� };

Point p;� � struct Line {� Point p1, p2;� };

Line l;

​

�

struct Triangle { � Point p1, p2, p3;�};

Triangle t;

(p.x, p.y)

(l.p1.x, l.p1.y)

(l.p2.x, l.p2.y)

(t.p2.x, t.p2.y)

(t.p1.x, t.p1.y)

(t.p3.x, t.p3.y)

C++ Structs

CS-202 C. Papachristos

Nested Structures

A struct type can be a member of another struct.

• Program design w.r.t. inherent attributes.

​

Example:

struct Line {� Point p1, p2;� };

​

Line l1;

​

Line

l1

Type Definition

Variable Creation

C++ Structs

CS-202 C. Papachristos

Nested Structures

A struct type can be a member of another struct.

• NOTE: Cannot have recursion here !

​

Example:

struct StudentRecord {

char name[15];

int id;

char dept[5];

char gender;

StudentRecord emergContact;

};

​

NO

struct StudentRecord {

char name[15];

int id;

char dept[5];

char gender;

StudentRecord * emergContact;

};

YES !

Pointer of self-referencing type is allowed

C++ Structs

CS-202 C. Papachristos

Nested Structures

A struct type can be a member of another struct.

• Program design w.r.t. inherent attributes.

​

Example:

Point p;� Line l;

Triangle t;

p.x = 4.0;

p.y = 11.0;

(4.0, 11.0)

(2.0, 7.0)

(9.0, 8.0)

(6.0, 5.0)

(2.0, 0.0)

(8.0, 3.0)

Literals-based Initialization of every primitive data member

C++ Structs

CS-202 C. Papachristos

Nested Structures

A struct type can be a member of another struct.

• Program design w.r.t. inherent attributes.

​

Example:

Point p;� Line l;

Triangle t;

l.p1.x = 2.0;

l.p1.y = 7.0;

l.p2.x = 9.0;

l.p2.y = 8.0;

(4.0, 11.0)

(2.0, 7.0)

(9.0, 8.0)

(6.0, 5.0)

(2.0, 0.0)

(8.0, 3.0)

Literals-based Initialization of every primitive data member

C++ Structs

CS-202 C. Papachristos

Nested Structures

A struct type can be a member of another struct.

• Program design w.r.t. inherent attributes.

​

Example:

Point p;� Line l;

Triangle t;

t.p1.x = 6.0;

t.p1.y = 5.0;

t.p2.x = 8.0;

t.p2.y = 3.0;

t.p3.x = 2.0;

t.p3.y = 0.0;

(4.0, 11.0)

(2.0, 7.0)

(9.0, 8.0)

(6.0, 5.0)

(2.0, 0.0)

(8.0, 3.0)

Literals-based Initialization of every primitive data member

C++ Structs

CS-202 C. Papachristos

Nested Structures

A struct type can be a member of another struct.

• Program design w.r.t. inherent attributes.

​

Example:

Point p;� Line l;

p.x = 2.00;

p.y = 7.00;

l.p1 = p;

p.x = 9.00;

p.y = 8.00;

l.p2 = p;

(p.x, p.y)

(l.p1.x, l.p1.y)

(l.p2.x, l.p2.y)

(t.p2.x, t.p2.y)

(t.p1.x, t.p1.y)

(t.p3.x, t.p3.y)

Modification and Assignment to each struct data member

(Data-Copy)

C++ Structs

CS-202 C. Papachristos

Arrays of Structs

Arrays are homogeneous (one data type):

• Regular data type.

​

​

• Supported type can be struct.

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C++ Structs

CS-202 C. Papachristos

Arrays of Structs

Arrays are homogeneous (one data type):

​

​

• Supported type can be struct.

​

struct Point { � double x, y;�};

​

Point point_array[100];

C++ Structs

CS-202 C. Papachristos

Arrays of Structs

All aforementioned operations take place as usual:�

StudentRecord classRecords[100];� �

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Declaration

C++ Structs

CS-202 C. Papachristos

Arrays of Structs

All aforementioned operations take place as usual:�

StudentRecord classRecords[100];� strcpy(classRecords[98].name,"John Doe");� classRecords[98].id = 123;� strcpy(classRecords[98].dept,"CSE");� classRecords[98].gender = 'M';�

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Indexing & Member-Access

C++ Structs

CS-202 C. Papachristos

Arrays of Structs

All aforementioned operations take place as usual:�

StudentRecord classRecords[100];� strcpy(classRecords[98].name,"John Doe");� classRecords[98].id = 123;� strcpy(classRecords[98].dept,"CSE");� classRecords[98].gender = 'M';� classRecords[0] = classRecords[98];

​

Indexing & Assignment

C++ Structs

CS-202 C. Papachristos

Struct Arrays in Structs

Remember: Arrays can be struct members

struct Point { � double x, y;� };

struct Square { � Point p[4];� };

Square s;

​

(s.p[0].x, s.p[0].y)

(s.p[1].x, s.p[1].y)

(s.p[3].x, s.p[3].y)

(s.p[2].x, s.p[2].y)

0 1 2 3

C++ Structs

CS-202 C. Papachristos

Structs and Functions

Supported type for Function Parameters can be struct:

struct Point{ double x, y; };

• Pass-By-Value

double points_distance(Point p1, Point p2){� return sqrt((p1.x-p2.x)*(p1.x-p2.x)+(p1.y-p2.y)*(p1.y-p2.y);� }

​

Point p1, p2;

double p12_distance = points_distance(p1, p2);

​

Data-Copy operation

// need declaration before any mention

// of Point can be made in the program

C++ Structs

CS-202 C. Papachristos

Structs and Functions

Supported type for Function Parameters can be struct &:

struct Point{ double x, y; };

• Pass-by-Reference

void shift_point_upright(Point & p){� p.x += 1.0;

p.y -= 1.0;� }

​

Point p;

shift_point_upright(p);

​

No Data-Copy

Modifies struct members

// need declaration before any mention

// of Point can be made in the program

C++ Structs

CS-202 C. Papachristos

Structs and Functions

Supported type for Function Parameters can be struct const &:

struct Point{ double x, y; };

• Pass-by-const-Reference

bool is_point_inbounds(const Point & p){� return p.x>=0 && p.x<NUM_COLS && p.y>=0 && p.x<NUM_ROWS;

}

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Point p;

bool p_inbounds = is_point_inbounds(p);

​

No Data-Copy

// need declaration before any mention

// of Point can be made in the program

C++ Structs

CS-202 C. Papachristos

Structs and Functions

Supported type for Function Parameters can be struct &:

• Pass-by-Reference

void set_point_inbounds(Point & p){

if (p.x<0) p.x=0; else if (p.x>=NUM_COLS) p.x=NUM_COLS-1;� if (p.y<0) p.y=0; else if (p.y>=NUM_ROWS) p.y=NUM_ROWS-1;

}

• Pass-by-const-Reference

void set_point_inbounds(const Point & p){

if (p.x<0) p.x=0; else if (p.x>=NUM_COLS) p.x=NUM_COLS-1;� if (p.y<0) p.y=0; else if (p.y>=NUM_ROWS) p.y=NUM_ROWS-1;

}

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const-Reference will not allow mutation

C++ Structs

CS-202 C. Papachristos

Structs and Functions

Supported type for Function Parameters can be struct *:

struct Point{ double x, y; };

• Pass-by-Address

void shift_point_upright(Point * p){� (*p).x += 1.0;

(*p).y -= 1.0;� }

​

Point p;

Point * p_Pt = &p;

shift_point_upright(p_Pt);

Dereferencing to access Value-Pointed-By

Modifies struct members

// need declaration before any mention

// of Point can be made in the program

C++ Structs

CS-202 C. Papachristos

Structs and Functions

Supported type for Function Parameters can be struct []/*:

struct Point{ double x, y; };

• struct Array can be Passed-by-Address

void shift_points_downleft(Point * p_arr, int sz){

for (int i=0; i<sz; ++i){� p_arr[i].x -= 1.0;

p_arr[i].y += 1.0;

}� }

Point points_array[100];

shift_points_downleft(points_array, 100);

Modifies struct members

Parameter similarly as:

Point p_arr[]

// need declaration before any mention

// of Point can be made in the program

C++ Structs

CS-202 C. Papachristos

Structs and Functions

Supported return type for Functions can be struct:

struct Point{ double x, y; };

• return type can be struct Value

Point mirror_point(const Point & p_in){

Point p_out;� p_out.x = -p_in.x;

p_out.y = -p_in.y;

return p_out;� }

Point p1;

Point p1_mirrored = mirror_point(p1);

Local variable

Point p_out

Data-Copy (assignment)

Point p1_mirrored =

Lifetime?

// need declaration before any mention

// of Point can be made in the program

CS-202 C. Papachristos

Procedural

Focused on the question: “What should the program do next?” Structure program by:

• Splitting into sets of tasks and subtasks.
• Make functions for tasks.
• Perform them in sequence (computer).

Large amount of data and/or tasks makes projects/programs unmaintainable.

​

Object-Oriented (OO)

Package-up self-sufficient modular pieces of code.

The world is made up of interacting objects.

Pack away details into boxes (objects) keep them in mind in their abstract form.

Focus on (numerous) interactions.

• Encapsulation
• Inheritance
• Polymorphism

A collection of Objects

A hierarchy of functions

Remember: Procedural vs Object-Oriented

Remember: Procedural vs Object-Oriented

CS-202 C. Papachristos

The ATM Machine paradigm

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struct Date {

int day;

int month;

int year;

};

struct BankAccount {

char name[15];

int acountNo[10];

double balance;

Date birthday;

};

​

Remember: Classes

CS-202 C. Papachristos

Class

C++ Classes are very similar to C Structs, in that they both include user-defined sets of data items, which collectively describe some entity such as a Student, a Book, an Airplane, or a data construct such as a String, a ComplexNumber, etc…

​

​

Bank Account

account number

owner’s name

balance

interest rate

more?

deposit money

withdraw money

check balance

transfer money

more?

Operations

(behaviors)

Type

Attributes (state)

String

sequence of characters

encoding

more?

compute length

concatenate

test for equality

more?

C++ Structs

CS-202 C. Papachristos

Structs in C++

structs encapsulate related data.

• Member variables maintain each object’s state.
• All member “parts” by default are publicly accessible.

(later: Class members by default are private – internally accessible for a specific Object from own methods, i.e. functions)

​

When to use a struct (for now) :

• For things that are mostly data-oriented.

C++ Structs

CS-202 C. Papachristos

Structs in C++

structs encapsulate related data.

• Member variables maintain each object’s state.
• All member “parts” by default are publicly accessible.

(later: Class members by default are private – internally accessible for a specific Object from own methods, i.e. functions)

​

When to use a struct (for now) :

• For things that are mostly data-oriented.
• Are there data-only limitations?

Data sanity checking might be necessary!

struct Date {

int month;

int day;

int year;

};

Date bDay{2, 29, 2015};

Not a leap year!

C++ Structs

CS-202 C. Papachristos

Structs in C++

structs can have methods (i.e. functions).

• Actually in C++ struct and Class are very similar.
• Default access level (public vs private) is the difference of significance� from what we know so far.

structs can have: (– Note: like Classes do)

• Member variables
• Methods (i.e. Functions)
• Constructors, Destructors, etc. (more on these later)
• public, private, and protected attributes (more on these later)
• virtual functions (more on these later)

​

​

C++ Structs

CS-202 C. Papachristos

Struct Methods / Constructors / etc. in C++

struct Date {

int month, day, year;

​

Date(int m_month, int m_day, int m_year) :

month(m_month), day(m_day), year(m_year){

if (month<=0) month = 1;

if (day<=0) day = 1;

if (year<1985) year = 1985;

fixLeapDate();

}

void fixLeapDate(){

if (year ... && month ... && day ...){

day = ...;

}

}

};

Date bday(2, 29, 2015);

Not a leap year!

C++ Structs

CS-202 C. Papachristos

Struct Methods / Constructors / etc. in C++

struct Date {

int month, day, year;

​

Date(int m_month, int m_day, int m_year) :

month(m_month), day(m_day), year(m_year){

if (month<=0) month = 1;

if (day<=0) day = 1;

if (year<1985) year = 1985;

fixLeapDate();

}

void fixLeapDate(){

if (year ... && month ... && day ...){

day = ...;

}

}

};

Date bday(2, 29, 2015);

• Constructor call !

Not a leap year!

C++ Structs

CS-202 C. Papachristos

Struct Methods / Constructors / etc. in C++

struct Date {

int month, day, year;

​

Date(int m_month, int m_day, int m_year) :

month(m_month), day(m_day), year(m_year){

if (month<=0) month = 1;

if (day<=0) day = 1;

if (year<1985) year = 1985;

fixLeapDate();

}

void fixLeapDate(){

if (year ... && month ... && day ...){

day = ...;

}

}

};

Date bday(2, 29, 2015);

• Constructor call !

​

• Perform series of checks.
• Calls internal method on itself.

Not a leap year!

C++ Structs

CS-202 C. Papachristos

Struct Methods / Constructors / etc. in C++

Calling Member Methods (i.e. Member Functions)

• Member Access Operator (.) - Just like accessing a member.

struct Date {

int month, day, year;

​

Date(int m_month, int m_day, int m_year) :

month(m_month), day(m_day), year(m_year){ ... }

bool isLeapYear(){ ... return ... ; }

};

​

Date bday(2, 29, 2015);

bool leap_year = bDay . isLeapYear();

​

C++ Structs

CS-202 C. Papachristos

By the way … (OO in C)

​

typedef struct student_t Student;

​

​

struct student_t

{

char name[15];

int id;

Student * emergencyContact;

​

void (*ConstructStudent)();

Student * (*AddEmergContact)(Student *);

};

​

void construct_student() { ... }

Student * add_emerg_contact(Student *self) { ... }

typedef required

C++ Structs

CS-202 C. Papachristos

By the way … (OO in C)

​

typedef struct student_t Student;

​

​

struct student_t

{

char name[15];

int id;

Student * emergencyContact;

​

void (*ConstructStudent)();

Student * (*AddEmergContact)(Student *);

};

​

void construct_student() { ... }

Student * add_emerg_contact(Student *self) { ... }

void* (or worse) members required for�Constructors and Member Methods

By the way … (OO in C)

​

typedef struct student_t Student;

​

​

struct student_t

{

char name[15];

int id;

Student * emergencyContact;

​

void (*ConstructStudent)();

Student * (*AddEmergContact)(Student *);

};

​

void construct_student() { ... }

Student * add_emerg_contact(Student *self) { ... }

C++ Structs

CS-202 C. Papachristos

External Function Definitions required

C++ Structs

CS-202 C. Papachristos

By the way … (OO in C)

​

Did you know?

struct student_t

{ ...

void (*ConstructStudent)();

Student * (*AddEmergContact)(Student *);

};

void construct_student() { ... }

Student * add_emerg_contact(Student *self) { ... }

int main()

{

Student student_a;

student_a.ConstructStudent = &construct_student;

student_a.ConstructStudent();

}

​

Function Binding of members to external functions required !

C++ Structs

CS-202 C. Papachristos

By the way … (OO in C)

​

Thankfully C++ is much more Versatile, Expressive than that !

struct Student

{ ...

Student(); // constructor declaration

void AddEmergContact(Student *); // member method declaration

};

void Student::Student() { ... } // constructor definition

void Student::AddEmergContact(Student * other) { ... } // member method definition

int main()

{

Student student_a; // implicit Student() call

Student student_b; // implicit Student() call

​

student_a.AddEmergContact(&student_b); // direct method call by object

}

​

Time for Questions !

CS-202

CS-202 C. Papachristos