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Structures in Objective-C
Objective-C is an object-oriented programming language that extends the C language with object-oriented capabilities. It follows a bottom-up approach and supports both procedural and object-oriented paradigms. One of the data structures supported by Objective-C is the structure. This article covers how to define and use structures in Objective-C.
Structures
A structure is a user-defined data type in Objective-C that allows grouping different data types together. A structure enables you to combine multiple types of data into a single unit. For instance, if we want to store a student’s information, such as their name (string), trade (string), registration number (integer), and age (integer), we can use a structure.
Defining a Structure
A structure in Objective-C is created using the struct keyword, followed by the structure name. Within the structure, we can define multiple data members.
Syntax:
struct structure_name {
data_type1 member1;
data_type2 member2;
};
It’s possible to declare one or more variables of the structure type at the end of its definition (this step is optional).
Example:
We define a structure called student that holds two strings (for name and trade) and two integers (for registration number and age):
// Creating a structure to store student data
struct student {
NSString *name;
NSString *trade;
int regNo;
int age;
};
Initializing Structure Members
Unlike some other languages, structure members cannot be initialized during their declaration. Initialization occurs after creating a structure variable, using dot notation (.).
Example:
// Declaring and initializing structure members
struct student st1;
st1.name = @"Student 1";
st1.trade = @"Computer Science";
st1.regNo = 123;
st1.age = 21;
Accessing Structure Members
To access a structure’s data members, use dot notation (.). The structure variable’s name is followed by the dot and the member name.
Syntax:
struct structure_name variable_name;
variable_name.member1;
variable_name.member2;
Example:
// Objective-C program using structure to store student data
#import <Foundation/Foundation.h>
// Defining structure
struct student {
NSString *name;
NSString *trade;
int regNo;
int age;
};
int main() {
struct student st1, st2;
// Initializing st1
st1.name = @"Student1";
st1.trade = @"Computer Science";
st1.regNo = 123;
st1.age = 21;
// Initializing st2
st2.name = @"Student2";
st2.trade = @"Electronics";
st2.regNo = 987;
st2.age = 20;
// Printing st1 data
NSLog(@"Student 1 Name: %@\n", st1.name);
NSLog(@"Student 1 Trade: %@\n", st1.trade);
NSLog(@"Student 1 RegNo: %d\n", st1.regNo);
NSLog(@"Student 1 Age: %d\n", st1.age);
// Printing st2 data
NSLog(@"Student 2 Name: %@\n", st2.name);
NSLog(@"Student 2 Trade: %@\n", st2.trade);
NSLog(@"Student 2 RegNo: %d\n", st2.regNo);
NSLog(@"Student 2 Age: %d\n", st2.age);
return 0;
}
Output:
Student 1 Name: Student1
Student 1 Trade: Computer Science
Student 1 RegNo: 123
Student 1 Age: 21
Student 2 Name: Student2
Student 2 Trade: Electronics
Student 2 RegNo: 987
Student 2 Age: 20
Pointers to a Structure
Like primitive data types, you can have pointers to structures. The pointer is defined using the * symbol, similar to other types of pointers.
struct student *student_ptr;
You can store the address of a structure variable in the pointer by using the address-of operator (&):
student_ptr = &st1;
To access members of a structure via a pointer, use the arrow operator (->):
student_ptr->name
Example: Using Pointers to Access Structure Members
// Objective-C program using pointers to access structure members
#import <Foundation/Foundation.h>
// Defining structure
struct student {
NSString *name;
NSString *trade;
int regNo;
int age;
};
int main() {
struct student st1;
struct student *student_ptr;
student_ptr = &st1;
// Initializing st1
st1.name = @"Student1";
st1.trade = @"Computer Science";
st1.regNo = 123;
st1.age = 21;
// Printing st1 info using direct access
NSLog(@"Printing st1 info directly\n");
NSLog(@"Name: %@\n", st1.name);
NSLog(@"Trade: %@\n", st1.trade);
NSLog(@"RegNo: %d\n", st1.regNo);
NSLog(@"Age: %d\n", st1.age);
// Printing st1 info using pointer
NSLog(@"\nPrinting st1 info using pointer\n");
NSLog(@"Name: %@\n", student_ptr->name);
NSLog(@"Trade: %@\n", student_ptr->trade);
NSLog(@"RegNo: %d\n", student_ptr->regNo);
NSLog(@"Age: %d\n", student_ptr->age);
return 0;
}
Output:
Printing st1 info directly
Name: Student1
Trade: Computer Science
RegNo: 123
Age: 21
Printing st1 info using pointer
Name: Student1
Trade: Computer Science
RegNo: 123
Age: 21