How to Combine 2 Struct arrays in C - c

Question

iv tried a lot of solutions to try to get this working (i.e using memcpy etc) I cant seem to find the issue, depending on what I try I either end up with gibberish or SEGV
iv spent a lot of time already googling and trying different ways, i still cant figure out why the arrays won't combine successfully
#include <stdio.h>
#include <stdint.h>
#include <dirent.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <sys/syscall.h>
#include <unistd.h>
#define log_info printf
typedef struct
{
char* name;
//size_t size;
} entry_t;
/* qsort struct comparison function (C-string field) */
static int struct_cmp_by_name(const void* a, const void* b)
{
entry_t* ia = (entry_t*)a;
entry_t* ib = (entry_t*)b;
return strcmp(ia->name, ib->name);
/* strcmp functions works exactly as expected from comparison function */
}
entry_t* get_item_entries(const char* dirpath, int* count)
{
struct dirent* dent;
char buffer[512]; // fixed buffer
int dfd = 0,
n, r = 1; // item counter, rounds to loop
entry_t* p = NULL; // we fill this struct with items
loop:
n = 0;
printf("loop: %d, count:%d\n", r, *count);
// try to open dir
dfd = open(dirpath, O_RDONLY, 0);
if (dfd < 0)
{
printf("Invalid directory. (%s)\n", dirpath);
*count = -1;
return NULL;
}
else
{
printf("open(%s)\n", dirpath);
}
memset(buffer, 0, sizeof(buffer));
while (syscall(SYS_getdents, dfd, buffer, sizeof(buffer)) != 0)
{
dent = (struct dirent*)buffer;
while (dent->d_fileno)
{ // skip `.` and `..`
if (!strncmp(dent->d_name, "..", 2)
|| !strncmp(dent->d_name, ".", 1)) goto skip_dent;
// deal with filtering outside of this function, we just skip .., .
switch (r)
{ // first round: just count items
case 1:
{
// skip special cases
if (dent->d_fileno == 0) goto skip_dent;
break;
}
// second round: store filenames
case 0: p[n].name = strdup(dent->d_name); break;
}
n++;
skip_dent:
dent = (struct dirent*)((void*)dent + dent->d_reclen);
if (dent == (void*)&buffer[512]) break; // refill buffer
}
memset(buffer, 0, sizeof(buffer));
}
close(dfd);
// on first round, calloc for our list
if (!p)
{ // now n holds total item count, note it
p = calloc(n, sizeof(entry_t));
*count = n;
}
// first round passed, loop
r--; if (!r) goto loop;
// report count
printf("%d items at %p, from 1-%d\n", *count, (void*)p, *count);
/* resort using custom comparision function */
qsort(p, *count, sizeof(entry_t), struct_cmp_by_name);
// report items
//for (int i = 0; i < num; ++i) log_error( "%s", p[i].name);
return p;
}
int main(int argc, char* argv[])
{
int HDD_count = -1;
uint32_t total = -1;
int ext_count = -1;
entry_t* e = NULL;
entry_t *HDD = get_item_entries("/mnt/f/n", &HDD_count);
entry_t* ext = get_item_entries("/mnt/f/dls", &ext_count);
total = ext_count + HDD_count;
e = (entry_t*)malloc(sizeof *e * total);
if (e != NULL)
{
for (int i = 1; i < HDD_count; i++)
{
log_info("HDD[%i].name %s\n", i, HDD[i].name);
e[i].name = strdup(HDD[i].name);
}
for (int i = 1; i < ext_count; i++)
{
log_info("ext[%i].name %s\n", i, ext[i].name);
e[i + HDD_count].name = strdup(ext[i].name);
}
}
else
printf("Failed to Allocate the Array");
char tmp[256];
int i = 1, j;
for(j = 1; j <= total; j++)
{
snprintf(&tmp[0], 255, "%s", e[ j].name);
log_info("%i:%s\n", j , tmp);
}
return 0;
}

Answer 1

Here is a rewrite of a snippet of main() that I mentioned in my comment above:
#define CHECK(p, msg) if(!(p)) { printf("%s:%d: %s", __FILE__, __LINE__, msg); return 1;}
...
entry_t *HDD = get_item_entries("/mnt/f/n", &HDD_count);
CHECK(HDD, "HDD failed to get entries");
entry_t *ext = get_item_entries("/mnt/f/dls", &ext_count);
CHECK(ext, "ext failed to get entries");
uint32_t total = HDD_count + ext_count;
entry_t *e = malloc(total * sizeof(*e));
CHECK(e, "malloc failed");
for(int i = 0; i < HDD_count; i++) {
log_info("HDD[%i].name %s\n", i, HDD[i].name);
e[i].name = strdup(HDD[i].name);
}
// write a function instead of duplicating code?
for (int i = 0; i < ext_count; i++) {
log_info("ext[%i].name %s\n", i, ext[i].name);
e[HDD_count + i].name = strdup(ext[i].name);
}
It looks like a short lived program, but I would still free the values from strdup() and e itself.