segmentation fault using malloc - c

Question

I'm new to C, so this may be a silly question to ask:
What I want to do here is to input the data to the array of pointers to a structure and then print it out. But I get a segmentation fault when running into the insert function.
Below is my code
common.h
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
typedef struct book * Book;
struct book{
int id;
char *name;
};
extern int b_insert(Book *b, int id, char *name);
extern int b_print(Book books[], int len);
insert.c
#include "common.h"
int b_insert(Book *b, int id, char *name){
Book p;
p = (Book)malloc(sizeof(struct book));
p->id = id;
strcpy(p->name, name);
*b = p;
printf("success insert book:\n");
printf("\tID: %d Name: %s\n", (*b)->id, (*b)->name);
return 0;
}
int b_print(Book books[], int len){
int i;
printf("Book List\n");
for(i=0; i<len; i++){
printf("books[%d] = ID: %d, Name: %s\n", i, books[i]->id, books[i]->name);
}
return 0;
}
main.c
#include "common.h"
#define MAX 2
int main(){
Book books[MAX];
Book *b=books;
int i;
int id;
char name[10];
for(i=0; i<MAX; i++){
printf("please input new books info\n");
printf("ID: ");
scanf("%d", &id);
printf("Name: ");
scanf("%s", name);
if(b_insert(b, id, name) == -1){
printf("fail to insert\n");
}
b++;
}
b_print(books, MAX);
return 0;
}

Answer 1

Main problem:
Allocate memory for p->name before using
strcpy(p->name, name);
using malloc:
p->name = malloc(10); //Or some other size
Other problems:
Remove the cast here:
p = (Book)malloc(sizeof(struct book));
Why? Here is the answer
if(b_insert(b, id, name) == -1){ will never be true.
Check the result of malloc to check if it was successful in allocating memory.
Check the return value of all the scanfs to see if it was successful in scanning data.
Add a length modifier to the second scanf to prevent buffer overflows:
scanf("%9s", name); /* +1 for the NUL-terminator */

Answer 2

You're not allocating space for name:
int b_insert(Book *b, int id, char *name){
Book p;
p = malloc(sizeof(struct book));
if (p != NULL)
{
p->name = malloc(strlen(name)+1); // It allocates space where the input name will be copied.
if (p->name != NULL)
{
p->id = id;
strcpy(p->name, name);
*b = p;
printf("success insert book:\n");
printf("\tID: %d Name: %s\n", (*b)->id, (*b)->name);
}
else return -1; // No space to allocate string
}
else return -1; // No space to allocate struct
return 0;
}

Answer 3

As mentioned before, allocate space for p->name. You should probably also use something different to read the book title, either scanf format %ms with a pointer to a char pointer, or %9s with your buffer, otherwise the title "war or peace" will also result in a segfault.

Answer 4

Here you create a static variable and the space for it is allocated automatically.
Book p;
You can allocate a space manually when you assign it to pointer, in this line it's not pointer but static variable.
p = (Book)malloc(sizeof(struct book));
What's more if you want to refer to attribute of static variable you should use "." instead of "->". So you have two option. Create a pointer and allocate a space for the structure and then you "->" oraz create static variable.
p->id = id;