C Programming FAQs Errata
http://c-faq.com/book/Errata.html
Errata list for "C Programming FAQs: Frequently Asked Questions", by Steve Summit, Addison-Wesley, 1996, ISBN 0-201-84519-9 (first printing).
A possibly more up-to-date copy of this errata list may be obtained at any time by anonymous ftp from ftp.eskimo.com in the file ~scs/C-faq/book/Errata, or on the web at http://www.eskimo.com/~scs/C-faq/book/Errata.html . (If you read this years from now and those addresses don't work, try ftp://ftp.aw.com/cseng/authors/summit/cfaq/ or http://www.awl.com/cseng/titles/0-201-84519-9 .)
scs 2002-Oct-26
page question
-— –——
front cover The ladder has no rungs.
xxix "woundn't" should be "wouldn't"
2 1.1 The fourth bulleted guarantee (about the sizes following the "obvious progression") is improperly stated. What the C Standard actually talks about, as in the rest of this answer, is just the ranges of the standard types, not their sizes in bits. So the real guarantees (as summarized below) are that
sizeof(char) is at least 8 bits sizeof(short) is at least 16 bits sizeof(int) is at least 16 bits sizeof(long) is at least 32 bits
and, in C99,
sizeof(long long) is at least 64 bits
3-4 1.3 In C99, the new <inttypes.h> header provides Standard names for exact-size types: int16t, uint32t, etc.
4 1.4 In C99, long long is defined as an integer type with, in effect, at least 64 bits.
6 1.7 There may be zero definitions of an external function or variable that is not referenced in any expression. [Thanks and $1 to James Stern]
7 1.7 "use include to bring" should be "use #include to bring"
11 1.14 In the second fix, at the bottom of the page, it could conceivably be necessary to precede the line
typedef struct node *NODEPTR;
with the line
struct node;
for the reason mentioned on page 13, although in that case one of the two other fixes would clearly be preferable. [Thanks to James Stern]
13 1.15 In the alternate fix, at the bottom of the page, it could conceivably be necessary to precede the typedef declarations with the lines
struct a; struct b;
although again, putting those typedefs after the complete structure definitions would clearly be preferable in that case. [Thanks to James Stern]
18 1.22 The odd "return 0;" line is not really necessary.
20 1.24 Another possible arrangement is
* file1.h * #define ARRAYSZ 3 extern int array[ARRAYSZ];
* file1.c * #include "file1.h" int array[ARRAYSZ];
/* file2.c" #include "file1.h"
[Thanks to Jon Jagger]
23 1.29 [2nd bullet] "everything else termed" should be "everything else, termed"
24 1.29 [Rule 3] "if the header" should be "if any header". [Thanks and $1 to James Stern]
24 1.29 [Rule 4] "(i.e., function names)" should be "(e.g., function names)". [Thanks and $1 to James Stern]
24 1.29 The text at the bottom of the page suggests that "future directions" name patterns such as str[a-z]* are reserved only if their corresponding headers (e.g. <stdlib.h>) are included. The reserved function names are unconditionally reserved; it is only the macro names that are reserved only if the header is included. [Thanks and $1 to Mark Brader]
25 1.29 "if you don't include the header files" should be "if you don't include any header files".
32 2.4 Besides -> and sizeof, the . operator, as well as declarations of actual structures, also require the compiler to know more about the structure and so preclude incomplete or hidden definitions. [Thanks to James Stern]
33-36 2.6 In C99, a structure can contain a variable-length array (VLA) as its last member, providing a well-defined, Standard-compliant alternative.
38 2.10 C99 does have a way of generating anonymous structure values: "compound literals".
40 2.12 When trying to minimize wasted space in structures, array members should be ordered based on the size of their primitive types, not their overall size. [Thanks and $1 to James Stern]
43 2.20 "ANSI/SIO" should be "ANSI/ISO"
In C99, the "designated initializer" mechanism allows any member of a union to be initialized.
50 3.3 Of course, another way to increment i is i += 1. [Thanks to James Stern]
51 3.4 "higher precedence than *):" should be "higher precedence than *:"
52 3.6 Delete the close parenthesis at the end of the answer.
57 3.12 In C++, the prefix form ++i is preferred. [Thanks to James Stern]
68 4.5 The reference to ANSI Sec. 3.3.4 should say "esp. footnote 44". [Thanks to Willis Gooch]
72-3 4.10 In C99, it is possible to use a "compound literal" to generate a pointer to an (unnamed) constant value.
73 4.11 The reference to K&R2 sec. 5.2 should be pp. 95-7. [Thanks and $1 to Nikos Triantafillis]
75 4.13 "can interconverted" should be "can be interconverted". [Thanks and $1 to Howard Ham]
84 5.8 Either the comma or the parentheses in the answer should be changed.
95 6.2 The typography in the following line is inconsistent for the "x" of "x1".
104-5 6.15 C99 introduces variable-length arrays (VLA's) which, among other things, do allow declaration of a local array of size matching a passed-in array.
105-7 6.16 In C99, another solution is to use a variable-length array.
110 6.19 C99's variable-length arrays are also a nice solution to this problem.
115 7.1 The close parenthesis and period ")." at the bottom of the page are not part of the #define line.
121 7.9 There is an extra semicolon at the end of the first line of mymalloc's definition. [Thanks and $1 to Todd Burruss]
126 7.10 Missing "it"; should be "even if it is not dereferenced". [Thanks and $1 to Clinton Sheppard]
132 7.30 It would be even safer to add a second test on nchmax:
if(nchread >= nchmax) { nchmax += 20; if(nchread >= nchmax) { free(retbuf); return NULL; } newbuf = realloc(retbuf, nchmax + 1);
The concern is that, while reading a very long line, nchmax might overflow, wrapping back around to 0. [Thanks to Mark Brader]
134 7.32 C99's variable-length arrays (VLA's) can be used to more cleanly accomplish most of the tasks which alloca used to be put to.
136 8.1 "Although string literal" should be "Although a string literal"
136 8.2 C can be tricked into seeming to assign an array as a whole if you hide the array inside a structure or union. [Thanks and $1 to James Stern]
143 9.2 The example variable isvegetable should perhaps be named isvegetable to avoid naming conflicts (see question 1.29). [Thanks and $1 to Jon Jagger]
151 10.4 Extra space in "* (no trailing ; ) *".
152 10.6 [paragraph below bullets] "bring the header wherever" should be "bring the header in wherever"
158 10.15 If you have to, you can obviously #define a companion macro name for each typedef, and use #ifdef with that. [Thanks to James Stern]
161 10.21 The suggested replacement macro should parenthesize c:
#define CTRL(c) ((c) & 037)
[Thanks and $1 to James Stern]
163-4 10.29 C99 introduces formal support for macros with variable numbers of arguments.
164-5 10.27 The file parameter of the dbginfo() function and the fmt parameter of the debug() function could be of type const char *. [Thanks to James Stern]
168 11.1 The story has gotten longer: A new revision of the C Standard, "C99", has been ratified, superseding the original ANSI C Standard. This Errata list has been updated to note those answers in the book which have become dated due to C99 changes.
169-70 11.2 C99 is available in electronic form, for $18 from www.ansi.org .
174 11.10 As written, the "complicated series of assignments" of course includes some declarations and initializations. [Thanks to James Stern]
175 11.10 "e.g., (const char) * in this case" should be "e.g., (const char *) in this case"
"when the pointers which" should either be "when the pointers" or "with pointers which"
180 11.19 "questions 20.20" should be "question 20.20"
182 11.25 "The function offers" should be "The memmove function offers". [Thanks and $1 to Gordon Burditt]
183-4 11.27 In C99, external identifiers are required to be unique in the first 32 characters; C90's extremely Spartan limitation to six characters has been relaxed.
186 11.29 You may also need to rework calls to realloc that use NULL or 0 as first or second arguments (see question 7.30).
186 11.29 You may also need to rework conditional compilation involving #elif. See also the Rationale's list of "Quiet Changes" (see question 11.2). [Thanks to James Stern]
189 11.33 A fourth class of behavior is locale-specific. [Thanks and $1 to James Stern]
198 12.11 A semicolon is missing after "int i = 0".
The } just before the line "*p = '\0'" is indented one tab too few.
Two instances of "*–p" have the minus signs merged so as to appear as one.
201 12.16 [case 2] The variable line is not declared; it should probably be a char [], suitably initialized, e.g.:
char line[] = "1 2.3 4.5e6 789e10";
[Thanks and $1 to James Stern]
205 12.19 There's an extraneous double quote in what should be "intervening whitespace:".
207-8 12.21 The technique of writing to a file may give the wrong answer if the disk fills up. [Thanks and $1 to Mark Brader]
The "hope that a future revision of the ANSI/ISO C Standard will include" the snprintf function has been fulfilled: C99 does specify it. As a bonus, the C99 snprintf can be used to predict the size required for an arbitrary sprintf call, too – it can be called with a null pointer instead of a destination buffer (and 0 as the size of that nonexistent buffer) and it returns the number of characters it would have written.
212 12.28 The answer is in the wrong font.
213 12.30 Updating (overwriting) a text file in-place is not fully portable; the C Standard leaves it implementation-defined whether a write to a text file truncates it at that point. [Thanks and $1 to Tanmoy Bhattacharya]
224 13.4 "upper- or lowercase" should probably be "upper or lower case".
225 13.6 Since the fragment calls printf, it must #include <stdio.h>. [Thanks and $1 to James Stern]
226 13.6 [last code fragment] A declaration and initialization
char string[] = "this\thas\t\tmissing\tfield";
similar to the one on p. 225 should appear. [Thanks and $1 to Doug Liu]
227 13.6 Also, since the input string is modified, it must be writable; see question 1.32.
234 13.14 "timets" should perhaps be "timet's"
240 13.17 The code
srand((unsigned int)time((timet *)NULL));
though popular and generally effective is, alas, not strictly conforming. It's theoretically possible that timet could be defined as a floating-point type under some implementation, and that the timet values returned by time() could therefore exceed the range of an unsigned int in such a way that a well-defined cast to (unsigned int) is not possible.
242-3 13.20 The attributions listed for methods 2 and 3 are scrambled. Method 2 is the one described in the 1958 Box and Muller paper (as well as by Abramowitz and Stegun, apparently). Method 3 is originally due to Marsaglia.
244 13.21 If you're not familiar with the notation [0, 1), it means that drand48() returns a number x such that 0 <= x and x < 1.
250 14.5 The suggested expression should read
fabs(a - b) <= epsilon * fabs(a)
It performs poorly if a == 0.0 (which is another argument in favor of "mak[ing] the threshold a function of b, or of both a and b").
253 14.8 Of course, you can always compute pi using 4*atan(1.0) or acos(-1.0). [Thanks to James Stern and Clinton Sheppard]
253 14.9 C99 specifies isnan() and several other classification routines.
254-5 14.11 C99 supports complex as a standard type.
260-1 15.4 The first argument to vstrcat() could be const char *, as could the fmt argument to miniprintf(). [Thanks to James Stern]
264 15.5 The fmt argument to error() could be const char *.
269-71 15.12 The fmt arguments to faterror(), verror(), and error() could all be const char *.
274 16.4 [point 2] The problem could be caused by a setbuf or setvbuf buffer local to any function. [Thanks and $1 to James Stern]
276 16.7 Variable "s" isn't declared. It's pretty obvious what it should be, but to make it explicit, change the struct declaration to
struct mystruct { … } s;
[Thanks to Peter Hryczanek]
287 18.1 The URL in the list of metrics tools is really "http://www.qucis.queensu.ca:1999/Software-Engineering/Cmetrics.html".
294 18.13 The conventional spelling is "NetBSD". [Thanks and $1 to Peter Seebach]
294 18.14 Extra space in site which should be "sunsite.unc.edu".
296 18.16 Extra space in address which should be "archie@archie.cs.mcgill.ca".
308 19.11 Note that a test using fopen() is approximate; failure does not necessarily indicate nonexistence.
310 19.14 Updating (overwriting) a text file in-place is not fully portable; the C Standard leaves it implementation-defined whether a write to a text file truncates it at that point. [Thanks and $1 to Tanmoy Bhattacharya]
314 19.23 In C99, the guarantee on the possible size of a single object has been raised to 64K.
315 19.25 Use of the `volatile' qualifier is often appropriate when performing memory-mapped I/O. [Thanks to Lee Crawford]
317 19.27 The return value of system() is not guaranteed to be the command's exit status. [Thanks and $1 to Peter Seebach]
318 19.30 If you forget to call pclose, it's probably at least as likely that you'll run out of file descriptors as processes. [Thanks and $1 to Jens Schweikhardt]
319 19.31 argv2 may also be a null pointer. [Thanks and $1 to Tanmoy Bhattacharya]
324 19.42 "control characters, such as" should be "control characters such as"
339-40 The page break makes the code very hard to follow.
342-44 20.13 The tone of this question's answer can be read as suggesting that efficiency isn't important at all. That's not the case, of course – efficiency can very important, and poorly-written programs can run abysmally inefficiently.
The point is that there are good ways and bad ways of achieving an appropriate level of performance for a given program, and that (for example) picking a good algorithm tends to make a much bigger difference than does microoptimizing the coding details of a lesser algorithm.
346 20.17 Missing tab in line which should be
#define CODENONE 0
350 20.21 The overbars are misaligned.
355 20.29 "and computes that number" should either be "computed" or "and is computed".
363 [aggregate] Unions are not aggregates. [Thanks and $1 to Kinichi Kitano]
368 [parameter] Extraneous semicolon at end of line which should be
f(int i)
370-1 The glossary entry for "undefined" is misplaced. [Thanks and $1 to James Stern]
376 The two minus signs in the index entry for "– operator" overlap and appear to be one.
379 The pairs of underscores in the index entry for "FILE macro" overlap and might appear to be one.
382 The pairs of underscores in the index entry for "LINE macro" overlap and might appear to be one.
back cover "on the Usenet/Internet on the C FAQ" is muddled and should say something else.
"com.lang.c" should be "comp.lang.c".
The ftp address for source code should be ftp://ftp.aw.com/cseng/authors/summit/cfaq