C Structs and Pointers

1. Pointer to a Structure

You can create a pointer that points to a structure variable.
Useful when passing structures to functions or for dynamic memory allocation.

Syntax:

Access members using arrow -> operator instead of dot ..

2. Example: Basic Structure Pointer

#include <stdio.h>
#include <string.h>struct Student {
int id;
char name[50];
float marks;
};

int main() {
struct Student s1;
struct Student *ptr;

ptr = &s1; // pointer to structure

// Access members using pointer
ptr->id = 101;
strcpy(ptr->name, "Alice");
ptr->marks = 95.5;

printf("ID: %d\n", ptr->id);
printf("Name: %s\n", ptr->name);
printf("Marks: %.2f\n", ptr->marks);

return 0;
}

#include <stdio.h>

#include <string.h>struct Student {

int id;

char name[50];

float marks;

};

int main() {

struct Student s1;

struct Student *ptr;

ptr = &s1; // pointer to structure

// Access members using pointer

ptr->id = 101;

strcpy(ptr->name, "Alice");

ptr->marks = 95.5;

printf("ID: %d\n", ptr->id);

printf("Name: %s\n", ptr->name);

printf("Marks: %.2f\n", ptr->marks);

return 0;

}

Output:

ptr->member is equivalent to (*ptr).member.

3. Using Pointer with Array of Structures

#include <stdio.h>
#include <string.h>struct Student {
int id;
char name[50];
};

int main() {
struct Student students[2];
struct Student *ptr = students; // points to first element

ptr->id = 101;
strcpy(ptr->name, "Alice");

(ptr+1)->id = 102;
strcpy((ptr+1)->name, "Bob");

for(int i = 0; i < 2; i++) {
printf("ID: %d, Name: %s\n", (ptr+i)->id, (ptr+i)->name);
}

return 0;
}

#include <stdio.h>

#include <string.h>struct Student {

int id;

char name[50];

};

int main() {

struct Student students[2];

struct Student *ptr = students; // points to first element

ptr->id = 101;

strcpy(ptr->name, "Alice");

(ptr+1)->id = 102;

strcpy((ptr+1)->name, "Bob");

for(int i = 0; i < 2; i++) {

printf("ID: %d, Name: %s\n", (ptr+i)->id, (ptr+i)->name);

}

return 0;

}

Output:

4. Passing Structure Pointer to Function

Passing a structure pointer to a function avoids copying the whole structure.

#include <stdio.h>
#include <string.h>struct Student {
int id;
char name[50];
};

void printStudent(struct Student *s) {
printf("ID: %d, Name: %s\n", s->id, s->name);
}

int main() {
struct Student s1;
s1.id = 101;
strcpy(s1.name, "Alice");

printStudent(&s1); // pass pointer
return 0;
}

#include <stdio.h>

#include <string.h>struct Student {

int id;

char name[50];

};

void printStudent(struct Student *s) {

printf("ID: %d, Name: %s\n", s->id, s->name);

}

int main() {

struct Student s1;

s1.id = 101;

strcpy(s1.name, "Alice");

printStudent(&s1); // pass pointer

return 0;

}

Output:

5. Dynamic Memory Allocation with Struct Pointer

#include <stdio.h>
#include <stdlib.h>
#include <string.h>struct Student {
int id;
char name[50];
};

int main() {
struct Student *s = (struct Student*)malloc(sizeof(struct Student));

s->id = 101;
strcpy(s->name, "Alice");

printf("ID: %d, Name: %s\n", s->id, s->name);

free(s); // free allocated memory
return 0;
}

#include <stdio.h>

#include <stdlib.h>

#include <string.h>struct Student {

int id;

char name[50];

};

int main() {

struct Student *s = (struct Student*)malloc(sizeof(struct Student));

s->id = 101;

strcpy(s->name, "Alice");

printf("ID: %d, Name: %s\n", s->id, s->name);

free(s); // free allocated memory

return 0;

}

malloc allocates memory dynamically for a structure.
Always use free() to release memory.

6. Key Points About Structs and Pointers

Use struct StructName *ptr to create a structure pointer.
Access members using arrow -> (ptr->member).
Arrays of structures can be accessed using pointer arithmetic ((ptr+i)->member).
Passing structure pointers to functions saves memory.
Combine with malloc for dynamic memory allocation.
(*ptr).member is equivalent to ptr->member (less convenient).

C Structs and Pointers

1. Pointer to a Structure

2. Example: Basic Structure Pointer

3. Using Pointer with Array of Structures

4. Passing Structure Pointer to Function

5. Dynamic Memory Allocation with Struct Pointer

6. Key Points About Structs and Pointers

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C Structs and Pointers

1. Pointer to a Structure

2. Example: Basic Structure Pointer

3. Using Pointer with Array of Structures

4. Passing Structure Pointer to Function

5. Dynamic Memory Allocation with Struct Pointer

6. Key Points About Structs and Pointers

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