C++ replace data in binary file with fstream

I try to replace data in binary file using C++ and fstream library. Is it possible to do that with this library? I would like to print 5 bytes of file in address: 0xB03 and change the last of these bytes to 0.

I have written the following code snippet:

int getFileSize(std::string filename)
{
    std::ifstream in(filename, std::ifstream::ate | std::ifstream::binary);
    int retVal = in.tellg();
    in.close();
    return retVal;
}

int main()
{
    std::string filename;
    std::cout << "Please insert file path." << std::endl;
    std::getline(std::cin, filename);
    std::cout << "File size is " << getFileSize(filename) << std::endl;

    int address = 0xB03;
    unsigned int instLen = 5;
    char * instToChange = new char[instLen];

    std::ifstream input(filename, std::ios::binary);
    input.seekg(address);
    input.read(instToChange, instLen);
    input.close();

    std::cout << std::hex << (unsigned int)(instToChange[0] & 0x000000FF) << std::endl;
    std::cout << std::hex << (unsigned int)(instToChange[1] & 0x000000FF) << std::endl;
    std::cout << std::hex << (unsigned int)(instToChange[2] & 0x000000FF) << std::endl;
    std::cout << std::hex << (unsigned int)(instToChange[3] & 0x000000FF) << std::endl;
    std::cout << std::hex << (unsigned int)(instToChange[4] & 0x000000FF) << std::endl;

    instToChange[4] = (char)0x00;

    std::cout << std::hex << (unsigned int)(instToChange[0] & 0x000000FF) << std::endl;
    std::cout << std::hex << (unsigned int)(instToChange[1] & 0x000000FF) << std::endl;
    std::cout << std::hex << (unsigned int)(instToChange[2] & 0x000000FF) << std::endl;
    std::cout << std::hex << (unsigned int)(instToChange[3] & 0x000000FF) << std::endl;
    std::cout << std::hex << (unsigned int)(instToChange[4] & 0x000000FF) << std::endl;

    std::ofstream output(filename, std::ios::binary);
    output.seekp(address);
    output.write(instToChange, instLen);
    output.close();

    system("pause");
    return 0;
}

I have tried many versions of this code and I still can't understand why it doesn't work.