code question

**Richard Heathfield** · Sep 19 '08, 09:05 PM

Re: code question

Bill Cunningham said:

I have this code I would like to clean up.
>
#include <stdio.h>
#include <stdlib.h>
>
int main(int argc, char *argv[])
{
double x, y, a, b;
FILE *fp;
x = strtod(argv[1], NULL);
y = strtod(argv[2], NULL);
a = strtod(argv[3], NULL);
b = strtod(argv[4], NULL);
if ((fp = fopen(argv[4], "a")) == NULL) {
puts("fopen error");
exit(-1);
}
fprintf(fp, "%.2f\t%.2f\t%. 2f\t%.2f\n", x, y, a, b);
if (fclose(fp) == EOF) {
puts("fclose error");
exit(-1);
}
return 0;
}
>
If the program is run with no arguments I get a seg fault. If it is run
with 4, no problem. If it is run with less than four (that includes
argv[0]) then the program doesn't want to run right. How would I be able
to use this program with say one or two argvs ?

#include <stdio.h>
#include <stdlib.h>

#define DEFAULT_FILE_NA ME "foo.bar"

int main(int argc, char *argv[])
{
double x = 0.0, y = 0.0, a = 0.0, b = 0.0;
const char *filename = DEFAULT_FILE_NA ME;

FILE *fp = NULL;
if(argc 1)
{
x = strtod(argv[1], NULL);
}
if(argc 2)
{
y = strtod(argv[2], NULL);
}
if(argc 3)
{
a = strtod(argv[3], NULL);
}
if(argc 4)
{
b = strtod(argv[4], NULL);
filename = argv[4];
}
if ((fp = fopen(filename, "a")) == NULL) {
puts("fopen error");
exit(EXIT_FAILU RE);
}
fprintf(fp, "%.2f\t%.2f\t%. 2f\t%.2f\n", x, y, a, b);
if (fclose(fp) == EOF) {
puts("fclose error");
exit(EXIT_FAILU RE);
}
return 0;
}

--
Richard Heathfield <http://www.cpax.org.uk >
Email: -http://www. +rjh@
Google users: <http://www.cpax.org.uk/prg/writings/googly.php>
"Usenet is a strange place" - dmr 29 July 1999

**Ian Collins** · Sep 19 '08, 09:25 PM

Re: code question

Bill Cunningham wrote:

I have this code I would like to clean up.
>
#include <stdio.h>
#include <stdlib.h>
>
int main(int argc, char *argv[])
{
double x, y, a, b;
FILE *fp;
x = strtod(argv[1], NULL);
y = strtod(argv[2], NULL);
a = strtod(argv[3], NULL);
b = strtod(argv[4], NULL);
if ((fp = fopen(argv[4], "a")) == NULL) {
puts("fopen error");
exit(-1);
}
fprintf(fp, "%.2f\t%.2f\t%. 2f\t%.2f\n", x, y, a, b);
if (fclose(fp) == EOF) {
puts("fclose error");
exit(-1);
}
return 0;
}
>
If the program is run with no arguments I get a seg fault. If it is run with
4, no problem. If it is run with less than four (that includes argv[0]) then
the program doesn't want to run right. How would I be able to use this
program with say one or two argvs ?
>

Your requirements are incomplete.

What should happen if there are less than four arguments? Should a file
be opened? Should an error message be output?

Without these details, there a number of conflicting possible solutions.

--
Ian Collins.

**Bill Cunningham** · Sep 19 '08, 09:25 PM

Re: code question

"Richard Heathfield" <rjh@see.sig.in validwrote in message
news:wL2dnfcbMf wWj0nVRVnyigA@b t.com...

#include <stdio.h>
#include <stdlib.h>
>
#define DEFAULT_FILE_NA ME "foo.bar"
>
int main(int argc, char *argv[])
{
double x = 0.0, y = 0.0, a = 0.0, b = 0.0;
const char *filename = DEFAULT_FILE_NA ME;
>
FILE *fp = NULL;
if(argc 1)
{
x = strtod(argv[1], NULL);
}
if(argc 2)
{
y = strtod(argv[2], NULL);
}
if(argc 3)
{
a = strtod(argv[3], NULL);
}
if(argc 4)
{
b = strtod(argv[4], NULL);
filename = argv[4];
}
if ((fp = fopen(filename, "a")) == NULL) {
puts("fopen error");
exit(EXIT_FAILU RE);
}
fprintf(fp, "%.2f\t%.2f\t%. 2f\t%.2f\n", x, y, a, b);
if (fclose(fp) == EOF) {
puts("fclose error");
exit(EXIT_FAILU RE);
}
return 0;
}

Thanks Richard I know I can always count on you. I wondered about argc
and its uses.

Bill

**Martin Ambuhl** · Sep 19 '08, 09:25 PM

Re: code question

Bill Cunningham wrote:

I have this code I would like to clean up.

Well, it certainly needs cleaning up, so you have got this part right.
See below.

If the program is run with no arguments I get a seg fault. If it is run with
4, no problem. If it is run with less than four (that includes argv[0]) then
the program doesn't want to run right. How would I be able to use this
program with say one or two argvs ?

There are many ways to hand differing numbers of arguments to a program.
Here is one way to start on yours, except that making your filename
argv[4] makes the exercise pointless.

#include <stdio.h>
#include <stdlib.h>

int main(int argc, char *argv[])
{
double x = 0, y = 0, a = 0, b = 0;
FILE *fp;
switch (argc) {
case 5:
b = strtod(argv[4], NULL);
case 4:
a = strtod(argv[3], NULL);
case 3:
y = strtod(argv[2], NULL);
case 2:
x = strtod(argv[1], NULL);
case 1:
break;
default:
fputs("I don't know how to handle that many arguments.\n",
stderr);
exit(EXIT_FAILU RE);
}
if (argc < 5) {
fprintf(stderr, "%s",
"I just wasted some time assigning values to x, y, a, &"
"b\nsince the fourth argument (argv[4]) is needed for a"
" filename\nand you didn't supply it.\n");
exit(EXIT_FAILU RE);
}
if ((fp = fopen(argv[4] /* this is nonsense, of course, if
argv < 5 */ , "a")) == NULL) {
fputs("fopen error\n", stderr);
exit(EXIT_FAILU RE); /* fixed non-portable 'exit(-1)' */
}
fprintf(fp, "%.2f\t%.2f\t%. 2f\t%.2f\n", x, y, a, b);
if (fclose(fp) == EOF) {
fputs("fclose error\n", stderr);
exit(EXIT_FAILU RE); /* fixed non-portable 'exit(-1)' */
}
return 0;
}

**Bill Cunningham** · Sep 19 '08, 09:45 PM

Re: code question

"Martin Ambuhl" <mambuhl@earthl ink.netwrote in message
news:gb1544$bmn $1@registered.m otzarella.org.. .

>
Well, it certainly needs cleaning up, so you have got this part right. See
below.
>
>
There are many ways to hand differing numbers of arguments to a program.
Here is one way to start on yours, except that making your filename
argv[4] makes the exercise pointless.
>
#include <stdio.h>
#include <stdlib.h>
>
int main(int argc, char *argv[])
{
double x = 0, y = 0, a = 0, b = 0;
FILE *fp;

Great. Switch. I've never used it before.

switch (argc) {
case 5:
b = strtod(argv[4], NULL);
case 4:
a = strtod(argv[3], NULL);
case 3:
y = strtod(argv[2], NULL);
case 2:
x = strtod(argv[1], NULL);
case 1:
break;
default:
fputs("I don't know how to handle that many arguments.\n",
stderr);

What's going on here? Is the default for more than the number of argv's
that the program calls for ? Why is there a break and not just default?

exit(EXIT_FAILU RE);
}
if (argc < 5) {
fprintf(stderr, "%s",
"I just wasted some time assigning values to x, y, a, &"
"b\nsince the fourth argument (argv[4]) is needed for a"
" filename\nand you didn't supply it.\n");
exit(EXIT_FAILU RE);
}
if ((fp = fopen(argv[4] /* this is nonsense, of course, if
argv < 5 */ , "a")) == NULL) {
fputs("fopen error\n", stderr);
exit(EXIT_FAILU RE); /* fixed non-portable 'exit(-1)' */
}
fprintf(fp, "%.2f\t%.2f\t%. 2f\t%.2f\n", x, y, a, b);
if (fclose(fp) == EOF) {
fputs("fclose error\n", stderr);
exit(EXIT_FAILU RE); /* fixed non-portable 'exit(-1)' */
}
return 0;
}

If exit(-1) is non -portable. Which I was afraid of what about exit(1)?
Or does the standard only allow exit(EXIT_FAILU RE);

Bill

**Bill Cunningham** · Sep 19 '08, 09:45 PM

Re: code question

"Ian Collins" <ian-news@hotmail.co mwrote in message
news:6jij2sF389 73U4@mid.indivi dual.net...

Your requirements are incomplete.
>
What should happen if there are less than four arguments? Should a file
be opened? Should an error message be output?
>
Without these details, there a number of conflicting possible solutions.
>

Yes if there are less than four arguments a file should be opened. There
must be a way to only write the fprintf stuff once though.

Bill

**Ian Collins** · Sep 19 '08, 10:25 PM

Re: code question

Bill Cunningham wrote:

"Ian Collins" <ian-news@hotmail.co mwrote in message
news:6jij2sF389 73U4@mid.indivi dual.net...
>

>Your requirements are incomplete.
>>
>What should happen if there are less than four arguments? Should a file
>be opened? Should an error message be output?
>>
>Without these details, there a number of conflicting possible solutions.
>>

Yes if there are less than four arguments a file should be opened. There
must be a way to only write the fprintf stuff once though.
>

The how about

#include <stdio.h>
#include <stdlib.h>

int main( int argc, char **argv )
{
double data[4] = {0.0};

if ( argc 5 ) {
puts("Too many arguments");
exit(EXIT_FAILU RE);
}

unsigned n = 1;

while ( n < argc ) {
data[n-1] = strtod(argv[n], NULL);
++n;
}

FILE *fp = fopen(argv[n-1], "a");

if ( fp == NULL ) {
puts("fopen error");
exit(EXIT_FAILU RE);
}

fprintf(fp, "%.2f\t%.2f\t%. 2f\t%.2f\n", data[0], data[1], data[2],
data[3]);

if (fclose(fp) == EOF ) {
puts("fclose error");
exit(EXIT_FAILU RE);
}

return 0;
}

--
Ian Collins.

**Andrew Poelstra** · Sep 19 '08, 10:45 PM

Re: code question

On 2008-09-19, Bill Cunningham <nospam@nspam.i nvalidwrote:

>
Thanks Richard I know I can always count on you. I wondered about argc
and its uses.
>
>

In addition to argc, argv is also NULL terminated (IIRC!), so
you can loop through it without needed argc to find out when
to stop.

while(*argv)
{
process(*argv);
++argv;
}

--
Andrew Poelstra apoelstra@wpsof tware.net
That was a joke. Jokes in mathematics, are sometimes not funny.
-Veselin Jungic

**Richard Heathfield** · Sep 19 '08, 10:45 PM

Re: code question

Andrew Poelstra said:

<snip>

In addition to argc, argv is also NULL terminated (IIRC!),

YRC. argv[argc] is guaranteed to be a null pointer (even if argc is 0).

<snip>

--
Richard Heathfield <http://www.cpax.org.uk >
Email: -http://www. +rjh@
Google users: <http://www.cpax.org.uk/prg/writings/googly.php>
"Usenet is a strange place" - dmr 29 July 1999

**Richard** · Sep 19 '08, 11:35 PM

Re: code question

"Bill Cunningham" <nospam@nspam.i nvalidwrites:

I have this code I would like to clean up.
>
#include <stdio.h>
#include <stdlib.h>
>
int main(int argc, char *argv[])
{
double x, y, a, b;
FILE *fp;
x = strtod(argv[1], NULL);
y = strtod(argv[2], NULL);
a = strtod(argv[3], NULL);
b = strtod(argv[4], NULL);
if ((fp = fopen(argv[4], "a")) == NULL) {
puts("fopen error");
exit(-1);
}
fprintf(fp, "%.2f\t%.2f\t%. 2f\t%.2f\n", x, y, a, b);
if (fclose(fp) == EOF) {
puts("fclose error");
exit(-1);
}
return 0;
}
>
If the program is run with no arguments I get a seg fault. If it is
run with

Did you try it with a debugger? No? Then give up. Not that you need one
to spot the error. 10/10 for persistence. O/10 for originality. These
posts are getting a tad tiresome.

4, no problem. If it is run with less than four (that includes argv[0]) then
the program doesn't want to run right. How would I be able to use this
program with say one or two argvs ?
>
Bill
>
>

--

**Richard** · Sep 19 '08, 11:35 PM

Re: code question

"Bill Cunningham" <nospam@nspam.i nvalidwrites:

"Richard Heathfield" <rjh@see.sig.in validwrote in message
news:wL2dnfcbMf wWj0nVRVnyigA@b t.com...
>

>#include <stdio.h>
>#include <stdlib.h>
>>
>#define DEFAULT_FILE_NA ME "foo.bar"
>>
>int main(int argc, char *argv[])
>{
> double x = 0.0, y = 0.0, a = 0.0, b = 0.0;
> const char *filename = DEFAULT_FILE_NA ME;
>>
> FILE *fp = NULL;
> if(argc 1)
> {
> x = strtod(argv[1], NULL);
> }
> if(argc 2)
> {
> y = strtod(argv[2], NULL);
> }
> if(argc 3)
> {
> a = strtod(argv[3], NULL);
> }
> if(argc 4)
> {
> b = strtod(argv[4], NULL);
> filename = argv[4];
> }
> if ((fp = fopen(filename, "a")) == NULL) {
> puts("fopen error");
> exit(EXIT_FAILU RE);
> }
> fprintf(fp, "%.2f\t%.2f\t%. 2f\t%.2f\n", x, y, a, b);
> if (fclose(fp) == EOF) {
> puts("fclose error");
> exit(EXIT_FAILU RE);
> }
> return 0;
>}

>
Thanks Richard I know I can always count on you. I wondered about argc
and its uses.
>
Bill

You wondered about argc?

You never thought to

(a) see where it crashed using a debugger?
(b) examine the values of argc and argv in a debugger?

or

(c) read up about them in your copy of K&R2? Heathfield must really need
some soul cleansing if he responded to you with a total clean up with
no admonitions.

**Bill Cunningham** · Sep 20 '08, 12:15 AM

Re: code question

"Richard" <rgrdev@gmail.c omwrote in message
news:gb1clg$bg$ 1@registered.mo tzarella.org...

Did you try it with a debugger? No? Then give up. Not that you need one
to spot the error. 10/10 for persistence. O/10 for originality. These
posts are getting a tad tiresome.

So are yours Richard Good God so are yours.

Have a nice life..

**Bill Cunningham** · Sep 20 '08, 12:35 AM

Re: code question

Someone pointed out to me Richard that an answer to a question I raised
about bitwise operators was on page 49 or kandr2. I read, and re-read, and
re-read page 49 about 3 times and strained to keep my focus on reading and
the text. The question was why is the unary operator ~ shown like this:

x~34;
and not x=x~34;

Is the question indeed answered on that page?

Bill

**Barry Schwarz** · Sep 20 '08, 12:35 AM

Re: code question

On Fri, 19 Sep 2008 16:52:17 -0400, "Bill Cunningham"
<nospam@nspam.i nvalidwrote:

I have this code I would like to clean up.
>
>#include <stdio.h>
>#include <stdlib.h>
>
>int main(int argc, char *argv[])
>{
double x, y, a, b;
FILE *fp;
x = strtod(argv[1], NULL);
y = strtod(argv[2], NULL);
a = strtod(argv[3], NULL);
b = strtod(argv[4], NULL);

So the fourth command line argument should be a number.

if ((fp = fopen(argv[4], "a")) == NULL) {

At the same time, it should be a file name.

That doesn't strike you as slightly odd?

--
Remove del for email

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