Segmentation Fault outside the loop only - c

Question

Using C on Linux, I'm writing a code that stores all the information about the files in a directory using function stat() and prints them on the Terminal
The algorithm is quite simple, I made a structure array of "files" and dynamically allocated them. The structure contains a char array (string) so I dynamically allocated it too.
The thing is .. the dynamic allocation works fine but if I'm inside the while loop I can access the other element inside the structure - which is a structure stat object - but if I access it after the loop finishes, it gives me "Segmentation Fault"!
Here's the code
#include <string.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>
#include <time.h>
#include <pwd.h>
#include <grp.h>
#include <dirent.h>
struct file{
char* name;
struct stat fbuf;
};
int main(int argc, char **argv)
{
char* dir=NULL;
int k;
dir=(char *)malloc(strlen(argv[argc-1])+1);
dir=argv[argc-1];
strcpy(dir,argv[argc-1]);
DIR *curr_dir;
struct dirent *dir_inode;
int i,j=0;
char* sum=NULL;
struct file* files=NULL;
if ((curr_dir = opendir(dir)) == NULL) {
fprintf(stderr, "Can't Open %s\n", argv[1]);
exit(2);
}
while (((dir_inode = readdir(curr_dir))) != NULL) {
files=(struct file*) realloc(files,((j)+1)*(sizeof(char*)+sizeof(struct stat))); // Structure array reallocation
(files+(j))->name=(char *)(malloc(strlen(dir_inode->d_name)+1));//name allocation
for(i=0;i<strlen(dir_inode->d_name);i++)
(files+(j))->name[i]=dir_inode->d_name[i];//name storage
(files+(j))->name[i]='\0';
sum= (char *) malloc(strlen(dir)+strlen(dir_inode->d_name)+2);//To add file name to its directory
for(i=0;i<strlen(dir);i++)
sum[i]=dir[i];
sum[i]='/';
i++;
for(k=0;dir_inode->d_name[k]!='\0';k++)
sum[i+k]=dir_inode->d_name[k];
sum[i+k]='\0';//file name with directory in sum
if( stat(sum,&((files+j)->fbuf)) == -1){ // the function gets information from the file name and stores them in fbuf
printf("error stat\n");
exit(1);
}
free(sum);
if( S_ISDIR( ( (files+(j))->fbuf ).st_mode ) ){
printf("d");
}
else {
printf("-");
}
//Here the output appears fine
//The output depends on accessing fbuf in files array
printf("statOK\n");
(j)++; // index
}
printf("%d %d %d\n",files,j,files+1);
printf("%d\n",j);
printf("\n\n\n\n");
for(i=0;i<j;i++){
printf("%s\n",(files+i)->name);
printf("%d\n",files);
//Starting from here, same syntax but outside the loop it gives the error
if( S_ISDIR( ( (files+i)->fbuf ).st_mode ) ){
printf("d");
else {
printf("-");
}
}
free(files);
free(dir);
closedir(curr_dir);
exit(1);
}
The code isn't complete yet but all what I want is to access the fbuf outside the loop, then I can complete it
Any ideas?

Answer 1

Bad size assumption
This allocation is wrong:
files=(struct file*) realloc(files,((j)+1)*(sizeof(char*)+sizeof(struct stat)));
Here, you assumed that the size of struct file was the sum of the sizes of its two components. But in fact, you don't know how that structure is packed and aligned, so the size of struct file could be larger than what you thought. You should just be using sizeof(struct file) instead:
files=(struct file*) realloc(files,(j+1)*(sizeof(struct file)));