C/C++ Programmer's Guide (G06.25+)

Using the C Run-Time Library

HP C/C++ Programmer’s Guide for NonStop Systems—429301-008

4-3

Logical File Types

Regardless of the file-reference model you use, you specify the logical file type of a

physical file when you open the physical file. When selecting which logical type to use,

you must consider two factors:

1. Which of the logical types best matches the way you want to interpret the data in

the physical file

2. Whether the logical type chosen in Step 1 is available for the given physical file

type

The next two subsections describe how the two logical file types interpret and buffer

data.

Binary-Type Logical Files

The C run-time library interprets a binary-type logical file as a sequence of arbitrary

byte values. It does not translate data on input or output. Consequently, you control the

structure, content, and interpretation of a binary-type logical file.

Text-Type Logical Files

The C run-time library interprets a text-type logical file as a sequence of lines

containing ASCII text. Terminating each line of text is a newline character \n. In

addition, tab characters are converted to an appropriate number of spaces.

Both of the file-reference models perform line buffering of text files. However, both

models enable you to disable this buffering. In the ANSI model, the setnbuf()

function provides this service; in the alternate model, the fcntl() function does it.

Line buffering implies that data is buffered until a newline is transferred. However, the

C run-time library also flushes the buffer when:

•

The buffer becomes full. The maximum buffer sizes are listed in Table 4-1, Buffer

Sizes, on page 4-4.

•

You explicitly flush the buffer (using fflush() or fcntl()).

•

You make a call to fclose() or exit().

•

You make an input request of a nondisk file without flushing a series of output

requests (by sending a newline or flushing the buffer).