Glibc Error: double free or corruption - c++

Question

I have been looking around at the meaning of this error and it seems to mean that I am freeing the same object more than once. I can't seem to figure out how to prevent this. Any help or suggestions would be much appreciated.
File(randname)
File(a.out)
~File(a.out)
~Directory(randname)
~File(null)
~File()
*** glibc detected *** a.out: double free or corruption (fasttop): 0x0804b048 ***
======= Backtrace: =========
/lib/libc.so.6(+0x6ff0b)[0xb74baf0b]
/usr/local/gcc/gcc-cilk/lib/libstdc++.so.6(_ZdlPv+0x1f)[0xb7671b4f]
/usr/local/gcc/gcc-cilk/lib/libstdc++.so.6(_ZdaPv+0x1b)[0xb7671b9b]
a.out[0x8048983]
a.out[0x8048b12]
a.out[0x80487d7]
/lib/libc.so.6(__libc_start_main+0xf3)[0xb7464003]
a.out[0x8048701]
======= Memory map: ========
08048000-08049000 r-xp 00000000 00:25 268562602 /home/user/test/a.out
08049000-0804a000 r--p 00000000 00:25 268562602 /home/user/test/a.out
0804a000-0804b000 rw-p 00001000 00:25 268562602 /home/user/test/a.out
0804b000-0806c000 rw-p 00000000 00:00 0 [heap]
b7448000-b744b000 rw-p 00000000 00:00 0
b744b000-b75b2000 r-xp 00000000 08:01 1365267 /lib/libc-2.14.1.so
b75b2000-b75b4000 r--p 00167000 08:01 1365267 /lib/libc-2.14.1.so
b75b4000-b75b5000 rw-p 00169000 08:01 1365267 /lib/libc-2.14.1.so
b75b5000-b75b8000 rw-p 00000000 00:00 0
b75b8000-b75d3000 r-xp 00000000 08:01 1179017 /usr/local/gcc/gcc-cilk/lib/libgcc_s.so.1
b75d3000-b75d4000 r--p 0001a000 08:01 1179017 /usr/local/gcc/gcc-cilk/lib/libgcc_s.so.1
b75d4000-b75d5000 rw-p 0001b000 08:01 1179017 /usr/local/gcc/gcc-cilk/lib/libgcc_s.so.1
b75d5000-b75fe000 r-xp 00000000 08:01 1365275 /lib/libm-2.14.1.so
b75fe000-b75ff000 r--p 00028000 08:01 1365275 /lib/libm-2.14.1.so
b75ff000-b7600000 rw-p 00029000 08:01 1365275 /lib/libm-2.14.1.so
b7622000-b7624000 rw-p 00000000 00:00 0
b7624000-b770b000 r-xp 00000000 08:01 1179021 /usr/local/gcc/gcc-cilk/lib/libstdc++.so.6.0.19
b770b000-b770f000 r--p 000e7000 08:01 1179021 /usr/local/gcc/gcc-cilk/lib/libstdc++.so.6.0.19
b770f000-b7710000 rw-p 000eb000 08:01 1179021 /usr/local/gcc/gcc-cilk/lib/libstdc++.so.6.0.19
b7710000-b7718000 rw-p 00000000 00:00 0
b7718000-b7737000 r-xp 00000000 08:01 1365260 /lib/ld-2.14.1.so
b7737000-b7738000 r--p 0001f000 08:01 1365260 /lib/ld-2.14.1.so
b7738000-b7739000 rw-p 00020000 08:01 1365260 /lib/ld-2.14.1.so
bfa18000-bfa39000 rw-p 00000000 00:00 0 [stack]
ffffe000-fffff000 r-xp 00000000 00:00 0 [vdso]
Aborted
And here is the code:
#include <unistd.h>
#include <cstdio>
#include <cstring>
#include <iostream>
using namespace std;
class File
{
protected:
unsigned char recordLen;
unsigned location;
unsigned fileSize;
unsigned char filenameLen;
char* filename;
public:
File(){filename = NULL;}
File(FILE* readFromHere, const char* name)
{
recordLen = 152;
location = 20003;
fileSize = 16348;
filenameLen = strlen(name);
filename = new char[filenameLen + 1];
strcpy(filename, name);
cout << "File(" << filename << ")\n";
}
File(const File& o)
{
if (o.filename == NULL)
filename = o.filename;
else
{
filename = new char[o.filenameLen + 1];
strcpy(filename, o.filename);
}
}
~File()
{
if (filename)
cout << "~File(" << filename << ")\n";
else
cout << "~File(null)\n";
if (filename != NULL)
delete[] filename;
}
};
class Directory : public File
{
protected:
int numContents;
File* contents;
public:
Directory(FILE* readFromHere, const char* name)
: File(readFromHere, name)
{
numContents = 2;
contents = new File[numContents];
contents[0] = File(readFromHere, "a.out");
//~ contents[1] = File(readFromHere, "otherfile.cpp");
}
~Directory()
{
if (filename)
cout << "~Directory(" << filename << ")\n";
else
cout << "~Directory(null)\n";
if (contents != NULL)
delete[] contents;
}
};
int main()
{
Directory d(NULL, "randname");
sleep(2);
return 0;
}

Answer 1

Your class doesn't follow the Rule of Three even though it owns resources. You have a copy constructor and a destructor, but not a copy assignment operator. Which means that this line:
contents[0] = File(readFromHere, "a.out");
invokes the default copy assignment operator, which happily copies pointers. There's your double-deletion problem.