exc bad access - EXC_BAD_ACCESS error on fwrite using underlying array from vector class -

i stumped exc_bad_access error. using zlib compress , save data array ch in function deflatereadout called function generate. program fails @ fwrite on marked line.

class wsumap { public:   vector<vector <unsigned char> > chunk; int xcomp[4]; int ycomp[4]; vector<int> priority; hash hashchunk;  wsumap() {     chunk.resize(4);     chunk[0] = vector<unsigned char>(chunk);     chunk[1] = vector<unsigned char>(chunk);     chunk[2] = vector<unsigned char>(chunk);     chunk[3] = vector<unsigned char>(chunk);     priority.push_back(0);     priority.push_back(1);     priority.push_back(2);     priority.push_back(3);     xcomp[0] = -1;     xcomp[1] = -1;     xcomp[2] = -1;     xcomp[3] = -1;     ycomp[0] = -1;     ycomp[1] = -1;     ycomp[2] = -1;     ycomp[3] = -1; }  void generate() {     (int = 0; i<chunk; i++) {         chunk[0][i]=100;     }     (int = 0; < 16; i++) {         (int j = 0; j < 16; j++) {             cout << chunk[0][0] << endl;             unsigned char* ch = &chunk[0][0];             cout << ch[0] << endl;             deflatereadout(i, j, &chunk[0][0]);         }     } }  void deflatereadout(int x, int y, unsigned char* ch) {     int ret, flush;     unsigned have;     z_stream strm;     vector<unsigned char> out = vector<unsigned char>(chunk);     out.resize(chunk);      /* allocate deflate state */     strm.zalloc = z_null;     strm.zfree = z_null;     strm.opaque = z_null;     ret = deflateinit(&strm, z_default_compression);     if (ret != z_ok) assert(true);     //return ret;      ostringstream oss;     oss << "map/" << x << "x" << y;     string str = oss.str();     cout << str << endl;     file* dest = fopen(str.c_str(), "w");      /* run deflate() on input until output buffer not full, finish        compression if of source has been read in */     {         strm.avail_out = chunk;         strm.avail_in = chunk;         strm.next_in = ch;         strm.next_out = &out[0];          ret = deflate(&strm, z_finish); /* no bad return value */         assert(ret != z_stream_error); /* state not clobbered */          have = chunk - strm.avail_out;         if (fwrite(&out[0], 1, have, dest) != have || ferror(dest)) {//error here             (void) deflateend(&strm);             //return z_errno;         }      } while (strm.avail_out == 0);     assert(strm.avail_in == 0); /* input used */      /* clean , return */     (void) deflateend(&strm); } 

thank can provide.

i figured out. trying write directory did not exist , thought automatically create if did not exist.