On 3/27/2015 4:19 AM, Nils Stec wrote:
I wrote a patch for cat which shows the user some usage-information.
Jody Bruchon used write() for this purpose, other tools are using
fprintf(stderr, ....).
I don't know which i should prefer. In my opinion i would rather use
fprintf.
STDERR should be the output for operations, right?
Some of the programs already used write() and write() avoids dragging
the code in for the printf family of functions (all ELKS programs are
statically linked), so if there is NO usage of the printf family of
functions in the program, it may make sense to use write() to minimize
total program size. That being said, even a trivial usage message
should mention the program being run in the usage, and it's not a good
idea to assume that i.e. 'ls' is ALWAYS run as 'ls' since someone
could symlink or alias it in the future. Because of this,
fprintf(stderr, "usage: %s args\n", argv[0]);
is a thousand times better than:
write(STDERR_FILENO, "usage: ", 7);
write(STDERR_FILENO, argv[0], strlen(argv[0]));
write(STDERR_FILENO, "\n", 1);
This results in three calls to write() and a call to strlen() when we
could have just used one fprintf() to do all the work. In the future,
I think many calls to write() will be eliminated, since even one call
to a printf family function brings in the core code for all printf
functions anyway.
Is this the right way to write code for this project? It's the first
time I'm doing this in here and i don't wan't to do things wrong...
The cat patch should use fprintf(stderr, ...) since I've already
brought in the printf function family with my error_read: code and
write() is bad for the reasons outlined above.
A few other comments:
+#define NOT_OVERWRITING 0xABCD
...snip...
+ return NOT_OVERWRITING;
If the user asks you to not overwrite (clobber), you should silently
not clobber files and not consider it an error. If any program
succeeds in doing what the user asked for, it should return success
(0) with no messages. If you haven't read Eric S. Raymond's rules of
the Unix philosophy, take a look at them; I find them to be very
helpful guidelines when making program design decisions.
+ if (stat(srcname, &statbuf1) < 0) { // src nonexistent
You can't write comments using // unless you're using a C99 compiler.
bcc is a K&R C compiler that is not even guaranteed to be C89
compliant, so no // comments. Use /* comment */ instead. Source
comments are nice to have as long as they're not excessive or
explaining something that is very obvious.
+static int option_no_overwrite;
+static int option_verbose;
+static int option_interactive;
Depending on how many options you add, you may want to use one global
static int called 'flags' or similar, and use bit flags instead of a
bunch of ints. From the program 'fdupes' in one of my GitHub repos,
snipped up for brevity:
#define ISFLAG(a,b) ((a & b) == b)
#define SETFLAG(a,b) (a |= b)
#define F_RECURSE 0x0001
#define F_HIDEPROGRESS 0x0002
etc. etc.
...
switch (opt) {
case 'q':
SETFLAG(flags, F_HIDEPROGRESS);
break;
...
if (ISFLAG(flags, F_RECURSEAFTER)) <code here>...
if (!ISFLAG(flags, F_HIDEPROGRESS)) <code here>...
I don't necessarily recommend using this code, it's just an example
and it's written to be usable with more than one variable that holds a
set of flags. I'd rewrite it like this for ELKS programs to make it
cleaner:
static int flags;
#define ISFLAG(a) ((flags & a) == a)
#define SETFLAG(a) (flags |= a)
#define F_QUIET 0x0001
etc.
...
if (strcmp(argv[i], "-q")) SETFLAG(F_QUIET);
if (!ISFLAG(F_QUIET)) fprintf(stderr, "copied %d files\n", count);
---
+ if(option_verbose) {
+ printf("copied '%s' -> '%s'\n", srcname, destname);
+ }
Firstly, the output from GNU 'cp' looks like this:
$ cp -v foo/* bar/
'foo/1' -> 'bar/1'
'foo/2' -> 'bar/2'
'foo/3' -> 'bar/3'
I'd also prefer one-liners such as this with no multi-line 'else'
clause to be collapsed together (it makes the code easier to read and
avoids 'brace hell'). I also prefer that if, for, and while statements
have a space between the word and the (condition) part for the sake of
code readability. Write it like this instead:
if (option_verbose) printf("'%s' -> '%s'\n", srcname, destname);
Next:
+ // set defaults for options //
+ option_no_overwrite = 0;
+ option_verbose = 0;
+ option_interactive = 0;
The comment is unnecessary since it's obvious that "options are being
initialized to zero" by the code itself. This is self-commenting code.
I'd also prefer to see the variable names shortened a bit ('o_' or
'opt_' instead of 'option_' for example) and as mentioned previously,
it's probably better to use the bit flags method mentioned previously
if you're only using the variables as a yes/no flag.
+ arg_counter = 1; // start at argv[1]
+ options_counter = 0;
+ while(arg_counter < argc) {
+ if(!strcmp(argv[arg_counter], "-n")) {
+ options_counter++;
+ option_no_overwrite = 1;
+ }
+ if(!strcmp(argv[arg_counter], "-v")) {
+ options_counter++;
+ option_verbose = 1;
+ }
+ if(!strcmp(argv[arg_counter], "-i")) {
+ options_counter++;
+ option_interactive = 1;
+ }
+ if(!strcmp(argv[arg_counter], "-h")) goto usage;
+ arg_counter++;
+ }
- if ((argc > 3) && !dirflag) {
- fprintf(stderr, "%s: not a directory\n", lastarg);
+ if((argc > (3+options_counter)) && !dirflag) { // can't copy more
than one src-files into one dst-file
Ouch. Rather than try to explain the problems in detail, let me
rewrite it.
arg_cnt = 1; // start at argv[1]
opt_cnt = 0;
while(arg_cnt < argc) {
if (!strcmp(argv[arg_cnt], "-n")) {
opt_noclobber = 1;
} else if (!strcmp(argv[arg_cnt], "-v")) {
opt_verbose = 1;
} else if (!strcmp(argv[arg_cnt], "-i")) {
opt_interactive = 1;
} else if (!strcmp(argv[arg_cnt], "-h")) goto usage;
else break;
opt_cnt++;
arg_cnt++;
}
/* If multiple files specified, last one must be a directory */
if ((argc > (opt_cnt + 3)) && !dirflag) {
This rewrite combines all the option count increments into one
instance which reduces code size and stops parsing options at the
first non-option string. The comparison on the last line is more
readable and it is clearer that it is "comparing total argument count
to the number of options specified plus 3." The 'if-elseif-else' tree
stops processing once a valid option is hit and "falls through" once a
non-option is hit. It could (and probably should) be improved by
handling the combined option case such as 'cp -iv src dest' but this
is sufficient for now as long as the usage text implies that option
flags must be specified separately.
+ copy_count = 0;
+ file_count = 0;
+ while (argc-- > (2+options_counter)) {
+ srcname = argv[options_counter+1+file_count];
I've spent a lot of time cleaning these compressed mathematical
expressions out of the elkscmd code; let's not introduce more of them
(also shorten variable names while retaining their meaning, this is a
good example for why to use shorter names):
+ copy_cnt = 0;
+ file_cnt = 0;
+ while (argc-- > (opt_cnt + 2)) {
+ srcname = argv[opt_cnt + 1 + file_cnt];
Next,
- if (dirflag) destname = buildname(destname, srcname);
+ if(dirflag) destname = buildname(destname, srcname);
Don't do this, if no other reason than the fact that 'if' is not a
function call. I understand that it comes down to individual coding
style and the compiler doesn't care if you write
if((something+(q/2))==argv[x+2+y*z[aaa]])usage();
but it is hard to read and readability is very important. I believe
that 'if', 'while', and 'for' shouldn't look like function calls in
code since they are actually C control statements. Using a space makes
those control statements immediately obvious, whereas if() and while()
and for() look like function calls when skimming the code.
- if (!copyfile(*++argv, destname, 0)) goto error_copy;
+ retval = copyfile(srcname, destname, 0);
+ if((!retval) && (!(retval == NOT_OVERWRITING))) goto error_copy;
Remember the rule about silent success mentioned earlier? This change
can be eliminated because of it. Even if it wasn't, though, this code
could be simplified and made more readable in one shot:
+ retval = copyfile(srcname, destname, 0);
+ if (retval != 1) goto error_copy;
I'd actually recommend reversing the return values in copyfile(),
using nonzero as an error return instead (most C library calls seem to
use this convention and consistency with that is rarely a bad thing)
so you could just go:
+ if (retval) goto error_copy;
Next,
+ if(option_verbose) printf("copy-count = %d\n", copy_count);
This shouldn't be done. Here's GNU coreutils 'cp' in action:
file_utils $ cp -v foo/* bar/
'foo/COPYING' -> 'bar/COPYING'
'foo/COPYING.sash' -> 'bar/COPYING.sash'
'foo/Makefile' -> 'bar/Makefile'
'foo/README' -> 'bar/README'
'foo/WARRANTY' -> 'bar/WARRANTY'
...snip...
If someone is interested in knowing a "copy-count" for some reason,
they'll almost certainly do this instead:
file_utils $ cp -v foo/* bar/ | wc -l
46
Your helpful message will throw this off and make it not work as
expected. A shell script author will have to introduce an incompatible
kludge to their script to make up for 'cp' misbehaving, i.e.
CNT=$(cp -v $A/* $B/ | wc -l)
CNT=$((CNT - 1)) # This shouldn't be necessary...
Another problem is that you've declared a static global 'copy_count'
variable and you're introducing a local 'copy_count' variable as well.
It needs to be called something else for the sake of avoiding
programmer confusion. However, assuming you eliminate the "copy-count"
message I just talked about along with its local variable counterpart,
the global 'static unsigned int copy_count' is set (copy_count++) but
not used throughout the entire program and can be discarded.
If you ever want an "official" reference for how a particular elkscmd
program "should" behave, take a look at the POSIX standards:
http://pubs.opengroup.org/onlinepubs/9699919799/
Whew, that took me a long time to write. I hope it's helpful to you
and everyone else on the list. Thanks for your impressive work so far!
I'm looking forward to your finalized [PATCH] submissions. :-)
-Jody
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