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12.17 Text and Binary Streams

GNU systems and other POSIX-compatible operating systems organize all files as uniform sequences of characters. However, some other systems make a distinction between files containing text and files containing binary data, and the input and output facilities of ISO C provide for this distinction. This section tells you how to write programs portable to such systems.

When you open a stream, you can specify either a text stream or a binary stream. You indicate that you want a binary stream by specifying the ‘b’ modifier in the opentype argument to fopen; see Opening Streams. Without this option, fopen opens the file as a text stream.

Text and binary streams differ in several ways:

Since a binary stream is always more capable and more predictable than a text stream, you might wonder what purpose text streams serve. Why not simply always use binary streams? The answer is that on these operating systems, text and binary streams use different file formats, and the only way to read or write “an ordinary file of text” that can work with other text-oriented programs is through a text stream.

In the GNU C Library, and on all POSIX systems, there is no difference between text streams and binary streams. When you open a stream, you get the same kind of stream regardless of whether you ask for binary. This stream can handle any file content, and has none of the restrictions that text streams sometimes have.