Practical C Programming by Oualline Steve

Author:Oualline, Steve [Steve Oualline]
Language: eng
Format: epub
Tags: COMPUTERS / Programming Languages / C
ISBN: 9781449313043
Publisher: O'Reilly Media, Inc.
Published: 2011-07-12T16:00:00+00:00

Back in the dark ages BC (Before Computers), a magical device called a Teletype Model 33 existed. This amazing machine contained a shift register made out of a motor, with a rotor, and a keyboard ROM consisting solely of levers and springs. It contained a keyboard, a printer, and a paper tape reader/punch. It could transmit messages over the phones using a modem at the rate of 10 characters a second.

The Teletype had a problem. It took two-tenths of a second to move the printhead from the right side to the left. Two-tenths of a second is two character times. If a second character came while the printhead was in the middle of a return, that character was lost.

The Teletype people solved this problem by making end-of-line two characters: <RETURN> to position the printhead at the left margin and <LINE FEED> to move the paper up one line.

When the early computers came out, some designers realized that using two characters for end-of-line wasted storage (at this time, storage was very expensive). Some picked <LINE FEED> for their end-of-line, some <RETURN>. Some of the diehards stayed with the two-character sequence.

UNIX uses <LINE FEED> for end-of-line. The newline character, \n, is code 0x0A (LF or <LINE FEED>). MS-DOS/Windows uses the two characters: <RETURN><LINE FEED>. Apple uses <RETURN>.

MS-DOS/Windows compiler designers had a problem. What do we do about the old C programs that thought that newline was just <LINE FEED>? The solution was to add code to the I/O library that stripped out the <RETURN> characters from ASCII input files and changed <LINE FEED> to <LINE FEED> <RETURN> on output.

In MS-DOS/Windows, it makes a difference whether or not a file is opened as ASCII or binary. The flag b is used to indicate a binary file:

/* open ASCII file for reading */ ascii_file = fopen("name", "r"); /* open binary file for reading */ binary_file = fopen("name", "rb");

If you open a file that contains text as a binary file under MS-DOS/Windows, you have to handle the carriage returns in your program. If you open it as ASCII, the carriage returns are automatically removed by the read routines.

Question 14-2: The routine fputc can be used to write out a single byte of a binary file. Example 14-4 writes out numbers to 127 to a file called test.out. It works just fine on UNIX, creating a 128-byte-long file; however, on MS-DOS/Windows, the file contains 129 bytes. Why?

Example 14-4. wbin/wbin.c

[File: wbin/wbin.c] #include <stdio.h> #include <stdlib.h> #ifndef __MSDOS__ #include <unistd.h> #endif __MSDOS__ int main() { int cur_char; /* current character to write */ FILE *out_file; /* output file */ out_file = fopen("test.out", "w"); if (out_file == NULL) { fprintf(stderr,"Cannot open output file\n"); exit (8); } for (cur_char = 0; cur_char < 128; ++cur_char) { fputc(cur_char, out_file); } fclose(out_file); return (0); }

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