Glibcエラー：ダブルフリーまたは破損

私はこのエラーの意味を見回してきましたが、同じオブジェクトを複数回解放していることを意味しているようです。これを防ぐ方法がわからないようです。どんな助けや提案も大歓迎です。

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

そしてここにコードがあります：

#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;
}