一个奇怪的释放指针问题.求解决.delete,delete []都不行

去掉delete hex就正常了
delete [] hex;也不行
[解决办法]

if(hex != NULL)
 delete [] hex;

    unsigned char *hex;
    QString str="FF000200FF";
    int len=str.length();
    hex=new unsigned char[len/2];
    if(len%2==0){
        for(int i=0;i<=len/2;i++){
            hex[i]=strtoul(str.mid(i*2,2).toAscii().constData(),0,16);
        }
    }
    delete [] hex;
    hex=NULL;