Linked lists in c, struct of struct, segmentation fault

Question

I'm trying to implement a train structure in c. I have a struct called bogie and another called linked bogie. I'm having problems with how to refer to all components of these structures in the code. My main problems are:

-I get a seg fault while entering the bogie type

-Why is size of bogie 28? (char(1) +array(20) +int(4)=25)

-I want to confirm if there is a struct inside a struct,I need to malloc for every inner struct when i make an instance of the outer struct? Anyway to make this automatic.

-Am I over complicating the code? Is there a cleaner way to write this?

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

typedef struct
{
    char name;
    char type[20];
    int capacity;
}BOGIE;

struct LINKED_BOGIE
{
    BOGIE* bogie_part_address;
    struct LINKED_BOGIE* link;
};

typedef struct LINKED_BOGIE LINKED_BOGIE;


void print_train(LINKED_BOGIE* engine_address);
void add_bogie(LINKED_BOGIE* engine_address);


void add_bogie(LINKED_BOGIE* engine_address)
{
    LINKED_BOGIE* traverse=engine_address;
    LINKED_BOGIE* new_bogie_address=(LINKED_BOGIE*)malloc(sizeof(LINKED_BOGIE));
    new_bogie_ad:dress->bogie_part_address=(BOGIE*) malloc(sizeof(BOGIE));

    printf("Enter bogie name,type,capacity\n");
    scanf("%c%s%d",&(new_bogie_address->bogie_part_address->name),(new_bogie_address->bogie_part_address)->type,&((new_bogie_address->bogie_part_address)->capacity));


    do traverse=traverse->link;
    while(traverse->link!=NULL);

    traverse->link=new_bogie_address;
    new_bogie_address->link=NULL;
    print_train(engine_address);

}



void print_train(LINKED_BOGIE* engine_address)
{

    LINKED_BOGIE* traverse=engine_address;
    int count=0;
    printf("This is the train\n");
    printf("----------------------------------------\n");


    do
    {
        printf("Bogie number:%d\n",count);
        printf("Bogie name:%c\n",traverse->bogie_part_address->name);
        printf("Bogie type:%s\n",traverse->bogie_part_address->type);
        printf("Bogie capacity:%d\n",traverse->bogie_part_address->capacity);
        printf("----------------------------------------\n");
    }
    while(traverse->link!=NULL);

}

int main()
{

    printf("linked bogie size:%lu\n",sizeof(LINKED_BOGIE));
    printf("bogie size:%lu\n",sizeof(BOGIE));

    LINKED_BOGIE* engine_address=(LINKED_BOGIE*)malloc(sizeof(LINKED_BOGIE));
    engine_address->bogie_part_address=(BOGIE*)malloc(sizeof(BOGIE));

    engine_address->bogie_part_address->name='E';
    strcpy(engine_address->bogie_part_address->type,"Engine");
    engine_address->bogie_part_address->capacity=1;
    engine_address->link=NULL;

    //  print_train(engine_address);


    int choice=0;
    do
    {
        printf("Pick what you want to do:\n\
1)View the train\n\
2)Add a bogie\n\
3)Insert a bogie\n\
4)Remove a bogie\n\
5)Sort train\n\
6)Swap bogies\n\
7)Exit\n");

        scanf("%d",&choice);

        switch (choice)
        {
            case 1:print_train(engine_address);break;
            case 2:add_bogie(engine_address);
        }

    }

    while(choice!=7);




return 0;

}

Answer 1

Mike already explained that the size of the struct was caused by padding. In your system, an int uses 4 bytes and is aligned on a address multiple of 4.

Your mallocs are correct, but you will have to consistently free the inner and outer struct when later removing a boogie.

But you have small errors in your code:

• scanf("%c%s%d", ...) will not do what you expect: the %c is likely to read the end of the previous line and not the first non blank character. You should use a %1s for that, without forgotting a place for the null:

   char name[2]; ... scanf("%1s%19s%d",name,(new_bogie_address->bogie_part_address)->type, &((new_bogie_address->bogie_part_address)->capacity)); new_bogie_address->bogie_part_address->name = name[0]; 

• do traverse=traverse->link; while(traverse->link!=NULL); will not work either: when the train contains only one boogie, you set traverse to null before testing anything. You should do:

   while(traverse->link!=NULL) { traverse = traverse->link; } 

• in `print_traint, you forgot to move traverse. It should be:

   while(traverse != NULL) { .... traverse = traverse->link; count += 1; } 

Remember:

• %c is seldom used because it reads even non printable characters which are ignored by other formats
• do {...} while(...); if less used than the simple while(...) {...} because it runs its body at least once.