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@ -84,6 +84,7 @@ I'm vaccinated against COVID-19. Are you?
<A HREF="thegame" >/thegame</A>; <A HREF="thegame" >/thegame</A>;
<B>knowledge</B>: <B>knowledge</B>:
<A HREF="knowledge/cat/" >cat(1)</A>, <A HREF="knowledge/cat/" >cat(1)</A>,
<A HREF="knowledge/c78" >c78</A>,
<A HREF="knowledge/software">software</A>, <A HREF="knowledge/software">software</A>,
<A HREF="knowledge/true" >true(1)</A>, <A HREF="knowledge/true" >true(1)</A>,
<A HREF="knowledge/x200t" >X200T</A>; <A HREF="knowledge/x200t" >X200T</A>;

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<!DOCTYPE html>
<HTML LANG="en">
<HEAD>
<LINK HREF="http://www.trinity.moe/knowledge/c78" REL="canonical" />
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<META CONTENT="noindex" NAME="googlebot" /> <!-- FUCK GOOGLE -->
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<TITLE>K&R C</TITLE>
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<BODY>
<P><A HREF="/">~ Return to the rest of the site</A></P>
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<H1>K&R C</H1>
<H3>updated 2022-05-29</H3>
<HR ALIGN="left" SIZE="1" WIDTH="25%" />
<UL>
<LI><A HREF="https://archive.org/details/TheCProgrammingLanguageFirstEdition">The C Programming Language, 1st ed.</A> (The Internet Archive)</LI>
<LI><A HREF="https://www.bell-labs.com/usr/dmr/www/cman.pdf">C Reference Manual</A> (this paper bears striking similarity to and was also written by the author of Appendix A of <I>The C Programming Language, 1st ed.</I> - the chronology of these writings' release is unknown)</LI>
<LI><A HREF="https://arstechnica.com/features/2020/12/a-damn-stupid-thing-to-do-the-origins-of-c/">"A damn stupid thing to do" - the origins of C</A></LI>
<LI><A HREF="https://www.bell-labs.com/usr/dmr/www/chist.html">The Development of the C Language</A></LI>
<LI><A HREF="http://pdp11.aiju.de/">PDP-11 Emulator</A></LI>
</UL>
<P>
The C programming language was first described to the public in <I>The C Programming Language</I> by Brian W. Kernighan and Dennis M. Ritchie, published by Prentice Hall in 1978.
The language evolved out of the former B programming language, which was a product of Ken Thompson:
</P>
<PRE>"""</PRE>
<P>Challenged by McIlroy's feat in reproducing TMG, Thompson decided that Unix—possibly it had not even been named yet—needed a system programming language. After a rapidly scuttled attempt at Fortran, he created instead a language of his own, which he called B. B can be thought of as C without types; more accurately, it is BCPL squeezed into 8K bytes of memory and filtered through Thompson's brain. Its name most probably represents a contraction of BCPL, though an alternate theory holds that it derives from Bon [Thompson 69], an unrelated language created by Thompson during the Multics days. Bon in turn was named either after his wife Bonnie, or (according to an encyclopedia quotation in its manual), after a religion whose rituals involve the murmuring of magic formulas.</P>
<PRE>""" (<I>The Development of the C Language</I>)</PRE>
<P>[Thompson 69] references <CODE>K. Thompson, `Bon—an Interactive Language,' undated AT&amp;T Bell Laboratories internal memorandum (ca. 1969)</CODE>
- please get in touch if you have a hyperlink for this document as I can't find it indexed on any search engines.</P>
<P>
This language described in <I>The C Programming Language</I> isn't the C programming language known by most.
It was a pre-standardization, relatively prototypical C, and rather than being codified in ANSI its primary documentation was the book by Kernighan and Ritchie (this book would later be known colloquially as <I>K&amp;R</I>).
This was known as "pre-ANSI C" or "K&amp;R C" and dubbed "C78" for the purposes of naming this page, in the same style as the later "C89", described in ANSI X3.159-1989, or "C11", described in ISO/IEC 9899:2011.
"C78" was also the name given to historical C by the <CODE>c78(7)</CODE> manual page on FreeBSD 9.0.
</P>
<P>
"C78" is incompatible with "C89" and later standards.
This page documents those incompatibilities and relative oddities.
</P>
<P>
I have never done (and probably never will do) extensive programming in pre-ANSI C.
These incompatibilities were discovered out of Appendix C in <I>The C Programming Language, 2nd ed.</I> but are described further.
</P>
<H2><CODE>8</CODE> and <CODE>9</CODE> as valid octal digits</H2>
<PRE>
main()
{
int i;
for(i = 0; i &lt; 10; ++i)
printf("%c\t%o\n", i + '0', i);
}
</PRE>
<P>
In pre-ANSI C, <CODE>8</CODE> and <CODE>9</CODE> were valid octal digits corresponding to <CODE>10</CODE> and <CODE>11</CODE>.
This is documented in <I>The C Programming Language</I>, Appendix A, subsection 2.4.1, and evidenced by the preceding code block.
The following is output of the compiled program in UNIX V6 on an emulated PDP-11:
</P>
<PRE>
0 0
1 1
2 2
3 3
4 4
5 5
6 6
7 7
8 10
9 11
</PRE>
<P>
This behavior exists within <CODE>/usr/source/c/c0t.s</CODE>, which is a PDP-11 assembler file that parses integer constants (as far as I can tell).
This file provides <CODE>getnum</CODE>, a function used in <CODE>/usr/source/c/c00.c</CODE>.
My theory is that this behavior is a side-effect of a very efficient but imperfect method of parsing integer constants from a file stream,
and that this implementation was "good enough" and informally the behavior of a C compiler supplied invalid octal constants was just undefined.
</P>
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