> On Unix systems, at least, directories can be fopen()ed just like files, and they contain binary content.
Not sure what does POSIX specify about this, but trying to `fread()` (but not `fopen()`!) a directory on GNU/Linux results in an error:
```c
#include <errno.h>
#include <stdio.h>
#include <string.h>
char buf[256];
int main() {
int e;
size_t i;
FILE * f = fopen(".", "r");
printf("%p\n", f);
if (!f) return -1;
i = fread(buf, 1, sizeof buf, f);
e = errno;
printf("%llu %d %s\n", (unsigned long long)i, e, strerror(e));
fclose(f);
return 0;
}
```
```
0x55b11dfd7010
0 21 Is a directory
```