将图像作为二进制文件读取

Question

I was reading about this project on codeproject. It reads images as a binary object and then checks the first 10 bytes of its header. I wrote the following code to run on Windows machine:

int main () {

  std::ifstream is ("warren.jpg", std::ifstream::binary);
  if (is) {
    // get length of file:
   // is.seekg (0, is.end);
    int length = 11;
    is.seekg (0, is.beg);

    char * buffer = new char [length];


    std::cout << "Reading " << length << " characters... "<<endl;
    char c='b';
    for(int i=0;i<11;i++)
    {
        is>>c;
    cout<<c<<endl;  //this just prints b 10 times
    }

    // read data as a block:
    is.read (buffer,length-1);
    buffer[length-1]= '\0';

    if (is)
      std::cout << "all characters read successfully.";
    else
      std::cout << "error: only " << is.gcount() << " could be read";
    is.close();

    cout<<"data is "<<buffer<<endl;

    // ...buffer contains the entire file...

    delete[] buffer;
  }

  return 0;
}

The output was:

Reading 11 characters...
b
b
b
b
b
b
b
b
b
b
b
error: only 0 could be readdata is

So, I know that the first line

std::ifstream is ("warren.jpg", std::ifstream::binary);

was successful as the if clause was entered. But after that nothing is received as input. I know that as it is a binary input, formatted input like is >> c should not be used. But I wrote this only when is.read() was unsuccessful.

Can anyone please tell me what the problem is?

Answer 1

You will have to open your file with the both the ios::binary | ios::in ios::binary | ios::in flags:

std::ifstream ifs (L"c:\\james.rar", std::ios::binary | std::ios::in);