How can I open a stream in binary mode?, C++ FAQ

C++ FAQ / Section 15 / FAQ 15.12

Section 15:

15.1	Advantages of `<iostream>` over `<cstdio>`?
15.2	Understanding infinite loop when the input is invalid?
15.3	How can I get `std::cin` to skip invalid input characters?
15.4	How does that funky `while (std::cin >> foo)` syntax work?
15.5	Why does my input seem to process past the end of file?
15.6	Why is my program ignoring my input request after the first iteration?
15.7	Should I end my output lines with `std::endl` or `'\n'`?
15.8	How can I provide printing for my `class` `Fred`?
15.9	Using a `printOn()` method vs. a `friend` function?
15.10	How can I provide input for my `class` `Fred`?
15.11	Providing printing for an entire hierarchy of classes?
15.12	How can I open a stream in binary mode?
15.13	"Reopening" `std::cin` and `std::cout` in binary mode?
15.14	How can I write/read objects of my class to/from a data file?
15.15	Sending objects over a network?
15.16	Backslashes in filenames?
15.17	How to capture key presses before the ENTER key?
15.18	How to turn off screen echo on keyboard input?
15.19	How can I move the cursor around on the screen?
15.20	How can I clear the screen?
15.21	How can I change the colors on the screen?
15.22	How can I print the numeric value of a `char` or `char*`? Updated!

[15.12] How can I open a stream in binary mode?

Use std::ios::binary.

Some operating systems differentiate between text and binary modes. In text mode, end-of-line sequences and possibly other things are translated; in binary mode, they are not. For example, in text mode under Windows, "\r\n" is translated into "\n" on input, and the reverse on output.

To read a file in binary mode, use something like this:

#include <string>
#include <iostream>
#include <fstream>

void readBinaryFile(std::string const& filename)
{
  std::ifstream input(filename.c_str(), std::ios::in | std::ios::binary);
  char c;
  while (input.get(c)) {
    ...do something with c here...
  }
}

Note: input >> c discards leading whitespace, so you won't normally use that when reading binary files.