Conteúdo do Curso

C Structs

1. Introduction to Structs

What are Structs Structs Application Defining and Declaring Structs Creating Your First Struct Accessing Struct Fields

2. Pointers and Structs

Pointers Brief Overview Pointers to Structs Pointers Inside Structs Dynamically Allocating Structs Passing Structs to the Functions

3. Structs and Memory

Understanding Memory Layout of Structs Alignment and Padding in Structs Unions Arrays with Structs

4. Advanced Structs Usage

Nested Structs Struct with Arrays and Other Structs Anonymous Struct and Union Complex Data Structure

5. Implementing Data Structures

Introduction to Linked List Basic Concept and Structure Building a Linked List Travesting and Displaying Linked List Completion Overview

Alignment and Padding in Structs

Alignment

Each structure field is aligned to a boundary that is a multiple of the size of the structure's largest element.

For example, if the largest element is 4 bytes in size, then each element will be aligned on a 4-byte boundary.

This is done to speed up memory access and avoid hardware alignment problems.

main


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#include <stdio.h>

// simple struct 
struct Example {
    char a;
    int b;
    double c;
};

int main() {
    struct Example test;

    printf("Size of struct Example: %zu\n", sizeof(test));

    printf("Address of p.x (char): %p\n", &test.a);
    printf("Address of p.y (int): %p\n", &test.b);
    printf("Address of p.c (double): %p\n", &test.c);

    return 0;
}

The size of struct Example will be at least 16 bytes because double typically requires 8 byte alignment to be aligned on an 8-byte boundary. So the compiler will automatically add extra alignment bytes after int b so that double c starts on the correct boundary.

Padding

The char a field in the Example structure will only occupy 1 byte, since the char data type is typically 1 byte in size in C.

If the char a field is initialized with the character 'A', then only one byte will be occupied by that character, and the remaining bytes of the 'char a' field will remain uninitialized.

Note
The remaining bytes of the 'char a' field may contain garbage values that were in this memory location before the structure was initialized.

The int b field was required to make the compiler align the char a field with the int b field to demonstrate how the compiler automatically aligns and fills .

main


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#include <stdio.h>

// simple struct 
struct Example {
    char a;
    int b;
};

int main() {
    struct Example test = {'A'}; // fill in only one field

    printf("Size of struct Example: %zu\n", sizeof(test));

    unsigned char* ptr = (unsigned char*)&test;

    for (int i = 0; i < (sizeof(test) / 2); i++) 
    {
        printf("%p | value: %c\n", ptr + i, *(ptr + i));
    }
    return 0;
}

unsigned char* ptr = (unsigned char*)&test; - to view the structure byte by byte, you need to refer to memory as a sequence of bytes. The unsigned char type is used to represent unsigned bytes, allowing you to scan memory byte by byte;

(sizeof(test) / 2) - this restriction is necessary so that the loop processes only half of the structure - the char a field.

Tarefa

Create an unsigned char pointer to the test structure to traverse the allocated memory byte byte and perform explicit type casting;
In the loop conditions, specify the correct number of iterations to display all memory addresses of the char a field;
In the printf() function, write the correct expression to display addresses, taking into account address arithmetic.

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Seção 3. Capítulo 2

Alignment and Padding in Structs

Alignment

Each structure field is aligned to a boundary that is a multiple of the size of the structure's largest element.

For example, if the largest element is 4 bytes in size, then each element will be aligned on a 4-byte boundary.

This is done to speed up memory access and avoid hardware alignment problems.

main


              1234567891011121314151617181920
            
#include <stdio.h>

// simple struct 
struct Example {
    char a;
    int b;
    double c;
};

int main() {
    struct Example test;

    printf("Size of struct Example: %zu\n", sizeof(test));

    printf("Address of p.x (char): %p\n", &test.a);
    printf("Address of p.y (int): %p\n", &test.b);
    printf("Address of p.c (double): %p\n", &test.c);

    return 0;
}

Padding

The char a field in the Example structure will only occupy 1 byte, since the char data type is typically 1 byte in size in C.

If the char a field is initialized with the character 'A', then only one byte will be occupied by that character, and the remaining bytes of the 'char a' field will remain uninitialized.

Note
The remaining bytes of the 'char a' field may contain garbage values that were in this memory location before the structure was initialized.

The int b field was required to make the compiler align the char a field with the int b field to demonstrate how the compiler automatically aligns and fills .

main


              123456789101112131415161718192021
            
#include <stdio.h>

// simple struct 
struct Example {
    char a;
    int b;
};

int main() {
    struct Example test = {'A'}; // fill in only one field

    printf("Size of struct Example: %zu\n", sizeof(test));

    unsigned char* ptr = (unsigned char*)&test;

    for (int i = 0; i < (sizeof(test) / 2); i++) 
    {
        printf("%p | value: %c\n", ptr + i, *(ptr + i));
    }
    return 0;
}

(sizeof(test) / 2) - this restriction is necessary so that the loop processes only half of the structure - the char a field.

Tarefa

Create an unsigned char pointer to the test structure to traverse the allocated memory byte byte and perform explicit type casting;
In the loop conditions, specify the correct number of iterations to display all memory addresses of the char a field;
In the printf() function, write the correct expression to display addresses, taking into account address arithmetic.

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Seção 3. Capítulo 2

Alignment and Padding in Structs

Alignment

Each structure field is aligned to a boundary that is a multiple of the size of the structure's largest element.

For example, if the largest element is 4 bytes in size, then each element will be aligned on a 4-byte boundary.

This is done to speed up memory access and avoid hardware alignment problems.

main


              1234567891011121314151617181920
            
#include <stdio.h>

// simple struct 
struct Example {
    char a;
    int b;
    double c;
};

int main() {
    struct Example test;

    printf("Size of struct Example: %zu\n", sizeof(test));

    printf("Address of p.x (char): %p\n", &test.a);
    printf("Address of p.y (int): %p\n", &test.b);
    printf("Address of p.c (double): %p\n", &test.c);

    return 0;
}

Padding

The char a field in the Example structure will only occupy 1 byte, since the char data type is typically 1 byte in size in C.

If the char a field is initialized with the character 'A', then only one byte will be occupied by that character, and the remaining bytes of the 'char a' field will remain uninitialized.

Note
The remaining bytes of the 'char a' field may contain garbage values that were in this memory location before the structure was initialized.

The int b field was required to make the compiler align the char a field with the int b field to demonstrate how the compiler automatically aligns and fills .

main


              123456789101112131415161718192021
            
#include <stdio.h>

// simple struct 
struct Example {
    char a;
    int b;
};

int main() {
    struct Example test = {'A'}; // fill in only one field

    printf("Size of struct Example: %zu\n", sizeof(test));

    unsigned char* ptr = (unsigned char*)&test;

    for (int i = 0; i < (sizeof(test) / 2); i++) 
    {
        printf("%p | value: %c\n", ptr + i, *(ptr + i));
    }
    return 0;
}

(sizeof(test) / 2) - this restriction is necessary so that the loop processes only half of the structure - the char a field.

Tarefa

Create an unsigned char pointer to the test structure to traverse the allocated memory byte byte and perform explicit type casting;
In the loop conditions, specify the correct number of iterations to display all memory addresses of the char a field;
In the printf() function, write the correct expression to display addresses, taking into account address arithmetic.

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Alignment

Each structure field is aligned to a boundary that is a multiple of the size of the structure's largest element.

For example, if the largest element is 4 bytes in size, then each element will be aligned on a 4-byte boundary.

This is done to speed up memory access and avoid hardware alignment problems.

main


              1234567891011121314151617181920
            
#include <stdio.h>

// simple struct 
struct Example {
    char a;
    int b;
    double c;
};

int main() {
    struct Example test;

    printf("Size of struct Example: %zu\n", sizeof(test));

    printf("Address of p.x (char): %p\n", &test.a);
    printf("Address of p.y (int): %p\n", &test.b);
    printf("Address of p.c (double): %p\n", &test.c);

    return 0;
}

Padding

The char a field in the Example structure will only occupy 1 byte, since the char data type is typically 1 byte in size in C.

If the char a field is initialized with the character 'A', then only one byte will be occupied by that character, and the remaining bytes of the 'char a' field will remain uninitialized.

Note
The remaining bytes of the 'char a' field may contain garbage values that were in this memory location before the structure was initialized.

The int b field was required to make the compiler align the char a field with the int b field to demonstrate how the compiler automatically aligns and fills .

main


              123456789101112131415161718192021
            
#include <stdio.h>

// simple struct 
struct Example {
    char a;
    int b;
};

int main() {
    struct Example test = {'A'}; // fill in only one field

    printf("Size of struct Example: %zu\n", sizeof(test));

    unsigned char* ptr = (unsigned char*)&test;

    for (int i = 0; i < (sizeof(test) / 2); i++) 
    {
        printf("%p | value: %c\n", ptr + i, *(ptr + i));
    }
    return 0;
}

(sizeof(test) / 2) - this restriction is necessary so that the loop processes only half of the structure - the char a field.

Tarefa

Create an unsigned char pointer to the test structure to traverse the allocated memory byte byte and perform explicit type casting;
In the loop conditions, specify the correct number of iterations to display all memory addresses of the char a field;
In the printf() function, write the correct expression to display addresses, taking into account address arithmetic.

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Seção 3. Capítulo 2

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