C - Bubble Sort Program binary file - c

Question

I'm trying to make a Bubble Sort program in a binary file without using any arrays, instead of I will use fseek and fwrite functions.
Here is my code:
typedef struct{ //Films
short int year;
char title[LEN_NAME];
Genero_t gendre;
float rateIMDB;
}Ficha_t;
FILE * fd;
fd = fopen(name,"r+b");
Ficha_t aux1;
Ficha_t aux2;
int i,j,len;
if (fd != NULL)
{
rewind(fd);
fseek(fd, 0, SEEK_END);
len=ftell(fd);
rewind(fd);
for(i=0;i<len;i++);
{
for(j=0;j<len-1;j++)
{
fread(&aux1,sizeof(Ficha_t),1,fd);
fread(&aux2,sizeof(Ficha_t),1,fd);
if(strcmp(aux1.title,aux2.title)<0)
{
fseek(fd,-sizeof(Ficha_t)*2,SEEK_SET); //returning 2 positions for overwriting
fwrite(&aux2, sizeof(Ficha_t), 1, fd);
fwrite(&aux1, sizeof(Ficha_t), 1, fd);
fseek(fd,-sizeof(Ficha_t),SEEK_SET); //returning 1 position for checking again with the next film
}
}
}
}
It's not working since it's displaying the same 2 films, Where am I wrong? What could I do?

Answer 1

As mentioned in the comments, you want:
len=ftell(fd) / sizeof(Ficha_t);
to get the number of records in the file.
If you are trying to seek with offsets to the current location, use SEEK_CUR, not SEEK_SET.
I would add a bunch of printfs for ftell(fd) / sizeof(Ficha_t) so you can see that it's doing everything correctly. Also, you could be checking the return values of functions you are calling (they were probably returning errors as you tried to seek before the beginning and read/write there)

Answer 2

Specific code example:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <stdbool.h>
void fbubble_sort(const char *filename, size_t rec_size, bool (*needSwap)(const void *, const void *)){
FILE *fp = fopen(filename, "r+b");
if(!fp){
perror("fopen, r+");
exit(EXIT_FAILURE);
}
void *first = malloc(rec_size);
void *second = malloc(rec_size);
if(!first || !second){
perror("malloc");
exit(EXIT_FAILURE);
}
enum { NO_SWAP = -1};
long last_swap_pos;
do {
rewind(fp);
long pos_1 = 0;//first record position
last_swap_pos = NO_SWAP;
if(0==fread(first, rec_size, 1, fp))
break;
while((pos_1 <= last_swap_pos || last_swap_pos == NO_SWAP) && 1==fread(second, rec_size, 1, fp) ){
if(needSwap(first, second)){
fseek(fp, pos_1, SEEK_SET);
fwrite(second, rec_size, 1, fp);
fwrite(first, rec_size, 1, fp);
fflush(fp);
last_swap_pos = pos_1;
} else {
//exchange buffer
void *temp = first;
first = second;
second = temp;
}
pos_1 += rec_size;
}
}while(last_swap_pos != NO_SWAP);
free(first);free(second);
fclose(fp);
}
#define DATA_FILE "test.dat"
#define GREATERi(type, member)\
bool greater_i(const void *first, const void *second){\
return ((type*)first)->member > ((type*)second)->member;\
}\
/**/
#define GREATERs(type, member)\
bool greater_s(const void *first, const void *second){\
return strcmp((type*)first)->member, ((type*)second)->member) > 0;\
}\
/**/
#define LESSi(type, member)\
bool less(const void *first, const void *second){\
return ((type*)first)->member < ((type*)second)->member;\
}\
/**/
typedef struct {
unsigned v;
} Record;
GREATERi(Record, v)
int main(void){
void make_test_data(void);
void print_test_data(void);
make_test_data();
print_test_data();
fbubble_sort(DATA_FILE, sizeof(Record), greater_i);
print_test_data();
}
void make_test_data(void){
FILE *fp = fopen(DATA_FILE, "wb");
if(!fp){
perror("fopen, w");
exit(EXIT_FAILURE);
}
Record rec;
for(int i = 0; i < 100; ++i){
rec.v = rand() % 100;
fwrite(&rec, sizeof(rec), 1, fp);
}
fclose(fp);
}
void print_test_data(void){
FILE *fp = fopen(DATA_FILE, "rb");
if(!fp){
perror("fopen, r");
exit(EXIT_FAILURE);
}
Record rec;
int cnt = 0;
while(fread(&rec, sizeof(rec), 1, fp)){
if(cnt)
putchar(' ');
printf("%2u", rec.v);
if(++cnt == 10){
putchar('\n');
cnt = 0;
}
}
putchar('\n');
fclose(fp);
}