C - Segmentation fault : 11

Question

Hi I have to do a simulation of disk for my university.

I got 2 file :

tttfs.h :

#include <stdlib.h> #include <stdio.h> #include <stdint.h> typedef struct _disk disk; typedef struct _block block; struct _block{ uint8_t *unBlock; }; struct _disk{ int id; block *diskBlock; };

tfs_create.c :

#include "tttfs.h" uint8_t little[4]; int tttfs_create(int size, char *name); void inttolitend(uint32_t x, uint8_t* lit_int); int main(){ tttfs_create(7, "disk.tfs"); } int tttfs_create(int size, char *name){ FILE *f = NULL; if ((f = fopen(name, "wb"))!=NULL) { disk *d = malloc(sizeof(disk)); d->diskBlock = malloc(1024); d->id = 1; int i; for(i = 0; i<size; i++){ printf("%d\n", i); d->diskBlock[i].unBlock = malloc(1024); //I got the segmentation fault here } inttolitend(size, little); for(i = 0; i<4; i++){ d->diskBlock[0].unBlock[i] = little[i]; } for(i = 0; i<size; i++){ fwrite(&d->diskBlock[i],1024,1,f); } } else printf("Erreur\n\n"); return 0; } void inttolitend(uint32_t x, uint8_t* lit_int){ lit_int[3] = (uint8_t)x / (256*256*256); lit_int[2] = (uint8_t)(x % (256*256*256)) / (256*256); lit_int[1] = (uint8_t)((x % (256*256*256)) % (256*256)) / 256; lit_int[0] = (uint8_t)((x % (256*256*256)) % (256*256)) % 256; }

I want to write in a file a number of block (here 7), so I do malloc on size of my disk struct and then I do a malloc on diskBlock to make a table d->diskBlock[0].unBlock = malloc(1024); but not for more. how could I do a block[size] with my struct ? (I'm not good in c)

1. Alaways check the return value of malloc() against NULL. 2. Why this d->diskBlock = malloc(1024);? it should be malloc(size * sizeof(block));! — Iharob Al Asimi
– Iharob Al Asimi, Commented Jan 10, 2016 at 14:09
why d->diskBlock = malloc(1024);? Don't use magic numbers. — Sourav Ghosh
– Sourav Ghosh, Commented Jan 10, 2016 at 14:09
When you're doing d->diskBlock = malloc(1024) you allocate 1024 bytes not 1024 block structures. While it may not be the cause of your crash, it is a problem. — Some programmer dude
– Some programmer dude, Commented Jan 10, 2016 at 14:13
This fwrite(&d->diskBlock[i],1024,1,f); seems to be the problem, what are you trying with it? — Iharob Al Asimi
– Iharob Al Asimi, Commented Jan 10, 2016 at 14:13

Haris · Accepted Answer · 2016-01-10 14:11:33Z

1

I think you should change this line

d->diskBlock = malloc(1024);

to

d->diskBlock = malloc(sizeof(block) * size);

And, this

d->diskBlock[i].unBlock = malloc(1024);

to

d->diskBlock[i].unBlock = malloc(sizeof(uint8_t) * 4);

edited Jan 10, 2016 at 14:11

answered Jan 10, 2016 at 14:09

Haris

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2 Comments

Iharob Al Asimi Over a year ago

But I don't thikn this is triggering SIGSEGV. 1024 is enough space, more than enough. It would need maximum 7 * sizeof(block) or 56B approximately assuming 64 bit pointers.

Jackie Over a year ago

And how could I have a malloc(1024) on my block ? I need block[1024] length to simulate a disk.

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