Using pointer in structure and writing it file in C - c

Question

I was working on my college project in C and got some problem.
I used pointer to structure and used it to write in a file using fwrite but it isn't helping.Here is the code I used.
#include<stdio.h>
#include<stdlib.h>
#include<ctype.h>
#include<string.h>
#include<conio.h>
struct collection{
char *fname, *lname, *telephone, *address, *seat;
};
collection * alloc( ){
struct collection *r = (struct collection *) malloc (sizeof(collection*));
r->fname = NULL;
r->lname = NULL;
r->telephone = NULL;
r->address = NULL;
r->seat = NULL;
return (r);
}
void string_realloc_and_copy (char **dest, const char *src){
*dest =(char *) realloc (*dest, strlen (src) + 1);
strcpy (*dest, src);
}
int main(){
char ch = 'Y', temp[50];
FILE *ptf;
struct collection *asd;
asd = alloc();
//printf("%d",sizeof(asd));
//opening file
ptf = fopen("lang.txt","w+");
do{
printf("First name: ");
gets(temp);
string_realloc_and_copy(&asd->fname,temp);
printf("Last name: ");
gets(temp);
string_realloc_and_copy(&asd->lname,temp);
printf("Telephone: ");
gets(temp);
string_realloc_and_copy(&asd->telephone,temp);
printf("Address: ");
gets(temp);
string_realloc_and_copy(&asd->address,temp);
printf("Seat you want to book: ");
gets(temp);
string_realloc_and_copy(&asd->seat,temp);
fwrite(asd,12*sizeof(collection),1,ptf);
fflush(ptf);
//fprintf(ptf,"\n");
printf("Do you wish to enter another data...? (Y/N) ");
ch = getch();
}while((ch=toupper(ch))== 'Y');
rewind(ptf);
while(fread(asd,12*sizeof(collection),1,ptf) == 1){
printf("\n\n%s",asd->fname);
printf("\n\n%s",asd->lname);
printf("\n\n%s",asd->telephone);
printf("\n\n%s",asd->address);
printf("\n\n%s",asd->seat);
}
fclose(ptf);
}
It works until asd->telephone is reached it ask for address and goes unresponding. I could not figure out what i did wrong. I thought it was out of memory so i change
struct collection *r = (struct collection *) malloc (sizeof(collection*));
to
struct collection *r = (struct collection *) malloc (12*sizeof(collection*));
And it worked for some time and again same thing happened. I am using devC++ for compilation. Thanks in advance;

Answer 1

First you should not use gets() because its deprecated and there is no limit in how many characters it gets from stdin. I recommand you to use fgets. You should use malloc like this for a pointer
malloc(sizeof(*collection));
This way you allocate memory for a pointer.
And one another thing try this program with putc() and see if it works.

Answer 2

malloc (sizeof(collection*)) should be malloc(sizeof(*collection)). Your code is only allocating enough space for a pointer to the collection type, not the size of the structure that the collection pointer points to.
This also shows why it's a bad idea to use the same name for both a variable and a type. If you'd used different names, you would have gotten an error from the compiler. Use collection_t for the type.

Answer 3

Try sizeof (struct collection) without the *

Answer 4

i found so many changes in your code.First change is struct collection instead of collection .Second change is i used two file descriptors one for reading another one for writing.Third in your code you are initializing "asd" only once due to this it will write same structure every time into file . So i initialized inside do-while loop.Fourth one i used scanf instead of gets because when you are taking multiple inputs it's skipping some inputs.Fifth i removed 12 form fwrite and fread.Sixth i used one more getchar because we will press enter after giving seat number so ch is taking that enter to take the user input i had to use one more getcharFinally the changed code is
#include<stdio.h>
#include<stdlib.h>
#include<ctype.h>
#include<string.h>
//#include<conio.h>
struct collection
{
char *fname, *lname, *telephone, *address, *seat;
};
struct collection *alloc( ){
struct collection *r= malloc(sizeof(struct collection));
r->fname = NULL;
r->lname = NULL;
r->telephone = NULL;
r->address = NULL;
r->seat = NULL;
return (r);
}
void string_realloc_and_copy (char **dest, const char *src){
*dest =(char *) realloc (*dest, strlen (src) + 1);
strcpy (*dest, src);
}
int main(){
char ch = 'Y', temp[50];
FILE *ptf;
struct collection *asd;
//printf("%d",sizeof(asd));
//opening file
ptf = fopen("lang.txt","wb");
do{
asd = alloc();
printf("First name: ");
scanf("%s",temp);
string_realloc_and_copy(&asd->fname,temp);
printf("Last name: ");
scanf("%s",temp);
string_realloc_and_copy(&asd->lname,temp);
printf("Telephone: ");
scanf("%s",temp);
string_realloc_and_copy(&asd->telephone,temp);
printf("Address: ");
scanf("%s",temp);
string_realloc_and_copy(&asd->address,temp);
printf("Seat you want to book: ");
scanf("%s",temp);
string_realloc_and_copy(&asd->seat,temp);
fwrite(asd,sizeof(struct collection),1,ptf);
fflush(ptf);
//fprintf(ptf,"\n");
printf("Do you wish to enter another data...? (Y/N) ");
ch = getchar();
ch = getchar();
}while((ch=toupper(ch))== 'Y');
//rewind(ptf);
fclose(ptf);
FILE *ptf1;
ptf1 = fopen("lang.txt","rb");
while(fread(asd,sizeof(struct collection),1,ptf1)){
printf("\n\n%s",asd->fname);
printf("\n\n%s",asd->lname);
printf("\n\n%s",asd->telephone);
printf("\n\n%s",asd->address);
printf("\n\n%s",asd->seat);
}
fclose(ptf1);
}
and sample out put is