ferror leads to access violation - c++

Question

I get an Access Violation when calling ferror(f). The thing is I check that f isn't a null pointer. I'm also able to read out of the file, before I get the Access Violation. It happens in the bzip library from http://www.bzip.org, (which is only modified, so that it is possible to build, eg. disable error and remove the multiple main functions).
Here is the my main
int main() {
int e = 0;
int *error = &e;
FILE *f = fopen("./test", "r"); //open file
if (f == NULL) { //Changed, as beforehand both checks happend at the same time
//However the programm passes both checks
std::cout << "f* is NULL\n";
exit(1);
}
if (ferror(f)) {
std::cerr << "Can't open the file " << ferror(f) << '\n';
exit(1);
}
char *c = char[20];
fread(c, 1, 20, f); // Here we can read succesfully out of the file
std::cout << c;
BZFILE* bzfile = BZ2_bzReadOpen(error, f, 1, 0, NULL, 0); //The failing function call
}
Here is the function out of the library which fails:
BZFILE* BZ_API(BZ2_bzReadOpen)
( int* bzerror,
FILE* f,
int verbosity,
int small,
void* unused,
int nUnused )
{
bzFile* bzf = NULL;
int ret;
BZ_SETERR(BZ_OK);
if (f == NULL || //A check in the function itself, which also passes
(small != 0 && small != 1) ||
(verbosity < 0 || verbosity > 4) ||
(unused == NULL && nUnused != 0) ||
(unused != NULL && (nUnused < 0 || nUnused > BZ_MAX_UNUSED)))
{ BZ_SETERR(BZ_PARAM_ERROR); return NULL; };
if (ferror(f)) // Here is the access violation
{ BZ_SETERR(BZ_IO_ERROR); return NULL; };
}
The specific error is
Exception thrown at 0x0003E5C4 in wikiParser.exe: 0xC0000005: Access violation executing location 0x0003E5C4.
I tried moving the program to a different pc, however the same error still occurs. The pointer isn't NULL; there are two checks for that, and I can call ferror myself, without it being an access violation.

Answer 1

if(f == NULL || ferror(f)) // Check that f isn't NULL nor has an Error
std::cerr << "Can't open the file " << ferror(f) << '\n';
In other words, if f== NULL then cerr << ferror(f).
No wonder it blows up.