program bug

[Bill Cunningham]

I have looked this program up and down and I don't see what's wrong with
it. But it always breaks and gives me an error "mode error" no matter which
mode binary or text I choose. This simple program is supposed to take as
argv[1] a "b" or "t" for binary or text. It's not taking anything.

#include <stdio.h>

int main(int argc, char **argv) {
char *b;
int a;
FILE *ifp,*ofp;
if (argc!=4) {
fprintf(stderr, "usage error\n");
return -1;
}
if (argv[1]=="b") {
b="rb";
}
if (argv[1]=="t") {
b="rt";
}
if (argv[1]!="t"||argv[1]!="b") {
fprintf(stderr, "mode error\n");
return -1;
}
if ((ifp=fopen(arg v[2],b))==0) {
fprintf(stderr, "open error i\n");
return -1;
}
if ((ofp=fopen(arg v[3],b))==0) {
fprintf(stderr, "open error o\n");
return -1;
}
while(a!=EOF)
a=fgetc(ifp);
fputc(a,ofp);
printf("done\n" );
return 0;}

Is anyone good enough to glance at this and see what's wrong?

Bill

[Bill Cunningham]

Re: program bug

Well I now see I left out fclose I will correct that but I don't think
that's my problem.

Bill

[Robert Gamble]

Re: program bug

On May 2, 5:40 pm, "Bill Cunningham" <nos...@nspam.c omwrote:

I have looked this program up and down and I don't see what's wrong with
it. But it always breaks and gives me an error "mode error" no matter which
mode binary or text I choose. This simple program is supposed to take as
argv[1] a "b" or "t" for binary or text. It's not taking anything.
>
#include <stdio.h>
>
int main(int argc, char **argv) {
char *b;
int a;
FILE *ifp,*ofp;
if (argc!=4) {
fprintf(stderr, "usage error\n");
return -1;

Not a portable return value from main.

}
if (argv[1]=="b") {

This isn't doing what you think it is. This is comparing the address
of first program argument to the address of the string literal "b"
which will always be different. Either use (strcmp(argv[1], "b") ==
0) or say:

if (argv[1][0] == 'b') {

which will compare the first letter of the first argument to the
character constant b.

b="rb";
}
if (argv[1]=="t") {
b="rt";
}
if (argv[1]!="t"||argv[1]!="b") {
fprintf(stderr, "mode error\n");
return -1;
}
if ((ifp=fopen(arg v[2],b))==0) {
fprintf(stderr, "open error i\n");
return -1;
}
if ((ofp=fopen(arg v[3],b))==0) {
fprintf(stderr, "open error o\n");
return -1;
}
while(a!=EOF)

a is not initialized, referencing its value invokes undefined
behavior.

a=fgetc(ifp);
fputc(a,ofp);

I think you want braces around these statements, yes?

Try (not tested):

while ( (a = fgetc(ifp)) != EOF && fputc(a, ofp) != EOF )
;

printf("done\n" );

puts("done"); would work equally well.

return 0;}
>
Is anyone good enough to glance at this and see what's wrong?
>
Bill

--
Robert Gamble

[Robert Gamble]

Re: program bug

On May 2, 5:53 pm, "Bill Cunningham" <nos...@nspam.c omwrote:

Well I now see I left out fclose I will correct that but I don't think
that's my problem.
>
Bill

There were a number of problems with the program but as long as the
program was terminating normally the fclose() wasn't one of them, all
files are properly closed during normal program termination (although
it is usually a good idea to explicitly close files yourself).

--
Robert Gamble

[Bill Cunningham]

Re: program bug


"Robert Gamble" <rgamble99@gmai l.comwrote in message
news:2d73e006-fc0d-4ed7-ae1e-43535dea6140@8g 2000hse.googleg roups.com...

>a is not initialized, referencing its value invokes undefined

behavior.
>

> a=fgetc(ifp);
> fputc(a,ofp);

In the beginning a was declared. Is it not enough in this case to simply
declare an int? Or should I have done this int a=0; at the beginning of the
program?

Bill

[Bill Cunningham]

Re: program bug


"Robert Gamble" <rgamble99@gmai l.comwrote in message
news:2d73e006-fc0d-4ed7-ae1e-43535dea6140@8g 2000hse.googleg roups.com...

Not a portable return value from main.
>

> }
> if (argv[1]=="b") {

>
This isn't doing what you think it is. This is comparing the address
of first program argument to the address of the string literal "b"

Was declaring b as a pointer to char proper? Or should a simple b of
type char all that's needed?

which will always be different. Either use (strcmp(argv[1], "b") ==
0) or say:
>
if (argv[1][0] == 'b') {
>
which will compare the first letter of the first argument to the
character constant b.

I do not understand the above but it looks like a good way to write
code. Why is a zero used as the second dimension of this array?

Bill

[Joe Wright]

Re: program bug

Bill Cunningham wrote:

I have looked this program up and down and I don't see what's wrong with
it. But it always breaks and gives me an error "mode error" no matter which
mode binary or text I choose. This simple program is supposed to take as
argv[1] a "b" or "t" for binary or text. It's not taking anything.
>
#include <stdio.h>
>
int main(int argc, char **argv) {
char *b;
int a;
FILE *ifp,*ofp;
if (argc!=4) {
fprintf(stderr, "usage error\n");
return -1;
}
if (argv[1]=="b") {
b="rb";
}
if (argv[1]=="t") {
b="rt";
}
if (argv[1]!="t"||argv[1]!="b") {
fprintf(stderr, "mode error\n");
return -1;
}
if ((ifp=fopen(arg v[2],b))==0) {
fprintf(stderr, "open error i\n");
return -1;
}
if ((ofp=fopen(arg v[3],b))==0) {
fprintf(stderr, "open error o\n");
return -1;
}
while(a!=EOF)
a=fgetc(ifp);
fputc(a,ofp);
printf("done\n" );
return 0;}
>
Is anyone good enough to glance at this and see what's wrong?
>
Bill
>
>

You can't use == to compare strings. That's what strcmp() is for. This
is the first error I find, not the only one.

--
Joe Wright
"Everything should be made as simple as possible, but not simpler."
--- Albert Einstein ---

[Robert Gamble]

Re: program bug

On May 2, 6:16 pm, "Bill Cunningham" <nos...@nspam.c omwrote:

"Robert Gamble" <rgambl...@gmai l.comwrote in message
>
news:2d73e006-fc0d-4ed7-ae1e-43535dea6140@8g 2000hse.googleg roups.com...
>

a is not initialized, referencing its value invokes undefined

behavior.

>

a=fgetc(ifp);
fputc(a,ofp);

>
In the beginning a was declared. Is it not enough in this case to simply
declare an int? Or should I have done this int a=0; at the beginning of the
program?

You need to store a value into a variable before you use the value of
that variable, either through initialization (implicit or explicit) or
assignment. If you don't do this then the variable may contain
garbage ("indetermin ate value" in standards parlance), that garbage
may be a trap value which will invoke UB when read. Note that the
alternative I provided does not have this problem because "a" is
assigned before its value is used.

--
Robert Gamble

[Ian Collins]

Re: program bug

Bill Cunningham wrote:

I have looked this program up and down and I don't see what's wrong with
it. But it always breaks and gives me an error "mode error" no matter which
mode binary or text I choose. This simple program is supposed to take as
argv[1] a "b" or "t" for binary or text. It's not taking anything.
>
#include <stdio.h>
>
int main(int argc, char **argv) {
char *b;
int a;
FILE *ifp,*ofp;
if (argc!=4) {
fprintf(stderr, "usage error\n");
return -1;
}
if (argv[1]=="b") {
b="rb";
}
if (argv[1]=="t") {
b="rt";
}
if (argv[1]!="t"||argv[1]!="b") {
fprintf(stderr, "mode error\n");
return -1;
}
if ((ifp=fopen(arg v[2],b))==0) {
fprintf(stderr, "open error i\n");
return -1;
}
if ((ofp=fopen(arg v[3],b))==0) {
fprintf(stderr, "open error o\n");
return -1;
}
while(a!=EOF)
a=fgetc(ifp);
fputc(a,ofp);
printf("done\n" );
return 0;}
>
Is anyone good enough to glance at this and see what's wrong?
>

Someone stole the whitespace?

Why are you comparing characters with string literals? Surly your
compiler gave you some warnings?

--
Ian Collins.

[Bill Cunningham]

Re: program bug


"Ian Collins" <ian-news@hotmail.co mwrote in message
news:681is1F2qc 9btU19@mid.indi vidual.net...

Why are you comparing characters with string literals? Surly your
compiler gave you some warnings?
>

Not as whisper. As it is typed as is.

Bill

[Robert Gamble]

Re: program bug

On May 2, 6:28 pm, Ian Collins <ian-n...@hotmail.co mwrote:

Bill Cunningham wrote:

I have looked this program up and down and I don't see what's wrong with
it. But it always breaks and gives me an error "mode error" no matter which
mode binary or text I choose. This simple program is supposed to take as
argv[1] a "b" or "t" for binary or text. It's not taking anything.

>

#include <stdio.h>

>

int main(int argc, char **argv) {
char *b;
int a;
FILE *ifp,*ofp;
if (argc!=4) {
fprintf(stderr, "usage error\n");
return -1;
}
if (argv[1]=="b") {
b="rb";
}
if (argv[1]=="t") {
b="rt";
}
if (argv[1]!="t"||argv[1]!="b") {
fprintf(stderr, "mode error\n");
return -1;
}
if ((ifp=fopen(arg v[2],b))==0) {
fprintf(stderr, "open error i\n");
return -1;
}
if ((ofp=fopen(arg v[3],b))==0) {
fprintf(stderr, "open error o\n");
return -1;
}
while(a!=EOF)
a=fgetc(ifp);
fputc(a,ofp);
printf("done\n" );
return 0;}

>

Is anyone good enough to glance at this and see what's wrong?

>
Someone stole the whitespace?
>
Why are you comparing characters with string literals? Surly your
compiler gave you some warnings?

My compiler didn't provide any warnings for this code, did yours?

--
Robert Gamble

[Bill Cunningham]

Re: program bug


"Ian Collins" <ian-news@hotmail.co mwrote in message
news:681is1F2qc 9btU19@mid.indi vidual.net...

Someone stole the whitespace?

I was always told there were several choices in C indentation. These two
and maybe a third.

function { /*notice the one space after the first brace*/
} closing brace on a line by itself.
This is the style I use and another

function
{

body

}

With this style all braces are on lines by themselves.


Bill

[CBFalconer]

Re: program bug

Ian Collins wrote:

>

.... snip ...

>
Someone stole the whitespace?
>
Why are you comparing characters with string literals? Surly
your compiler gave you some warnings?

Surly compilers have that fault. :-)

--
[mail]: Chuck F (cbfalconer at maineline dot net)
[page]: <http://cbfalconer.home .att.net>
Try the download section.

** Posted from http://www.teranews.com **

[CBFalconer]

Re: program bug

Bill Cunningham wrote:

"Robert Gamble" <rgamble99@gmai l.comwrote in message
>

>a is not initialized, referencing its value invokes undefined
>behavior.
>>
> a=fgetc(ifp);
> fputc(a,ofp);

>
In the beginning a was declared. Is it not enough in this case to
simply declare an int? Or should I have done this int a=0; at the
beginning of the program?

You are using it before loading it. You want:

while (EOF != (a = fgetc(ifp))) fputc(a, ofp);

Note the use of blanks. As I recall there are other errors also.

--
[mail]: Chuck F (cbfalconer at maineline dot net)
[page]: <http://cbfalconer.home .att.net>
Try the download section.


** Posted from http://www.teranews.com **

[Ian Collins]

Re: program bug

Robert Gamble wrote:

On May 2, 6:28 pm, Ian Collins <ian-n...@hotmail.co mwrote:

>>
>Why are you comparing characters with string literals? Surly your
>compiler gave you some warnings?

>
My compiler didn't provide any warnings for this code, did yours?
>

Oops, my bad, I spotted the comparisons an didn't spot they were with
argv[n].

--
Ian Collins.