Why is that?

[Profetas]

I know what is causing the problem, but I couldn't
find out why.

#define newline "\n"
#define question_mark "\?"
#define single_quotas "\'"
#define double_quotas "\""
#define form_feed "\f"
#define horizontal_tab "\t"
#define vertical_tab "\v"
#define backslash "\\"
#include <stdio.h>

main(){
int var;
printf("Type a number:");
scanf("%d",&var );
printf("The number is ");
printf("%d",var );
printf(newline) ;

char *var2;
printf("Type a string:");
int bytes_read=0;
int nbytes = 100;

var2 = (char *) malloc (nbytes + 1);
bytes_read = getline (&var2, &nbytes, stdin);
if(bytes_read == -1)
{puts ("ERROR!: invalid input");}

printf("The string is ");
printf("%s",var 2);
printf(newline) ;
}

[Michael Mair]

Re: Why is that?

Hi Profetas,

[color=blue]
> I know what is causing the problem, but I couldn't
> find out why.[/color]

Very enlightening. What do you think your problem is?
Your code does not even compile...
[color=blue]
> #define newline "\n"
> #define question_mark "\?"
> #define single_quotas "\'"
> #define double_quotas "\""
> #define form_feed "\f"
> #define horizontal_tab "\t"
> #define vertical_tab "\v"
> #define backslash "\\"[/color]

Won't comment on the sense or nonsense of these macros.
Apart from the newline, you do not need that stuff. Please
keep your examples minimal.
[color=blue]
> #include <stdio.h>[/color]

Where is <stdlib.h> needed for malloc()?
And where is the header for the non-standard getline()
function? (see below, too)

[color=blue]
> main(){[/color]
int main ()
[color=blue]
> int var;
> printf("Type a number:");
> scanf("%d",&var );
> printf("The number is ");
> printf("%d",var );
> printf(newline) ;
>
> char *var2;
> printf("Type a string:");
> int bytes_read=0;
> int nbytes = 100;
>
> var2 = (char *) malloc (nbytes + 1);[/color]
You have been around here long enough: Do not cast the
result of malloc(). Btw: If you want to apply a cast,
then cast nbytes -- malloc takes a size_t argument.[color=blue]
> bytes_read = getline (&var2, &nbytes, stdin);[/color]
from 'man getline':
#define _GNU_SOURCE
#include <stdio.h>

ssize_t getline(char **lineptr, size_t *n, FILE *stream);
I do not know the return type ssize_t but the rest of the manpage
seems to tell me that it is an improved version of fgets() such
as most of us have in their personal library...
I would just make var2=NULL -- as getline is taking care of
allocation, this is alright for a short program.
[color=blue]
> if(bytes_read == -1)[/color]
bytes_read is not of type ssize_t.[color=blue]
> {puts ("ERROR!: invalid input");}[/color]
It might be another problem[color=blue]
>
> printf("The string is ");
> printf("%s",var 2);
> printf(newline) ;
> }[/color]
free() var2. Apart from that: Why use printf() for giving
a '\n'.

Please produce code that compiles for
gcc -ansi -pedantic
and then come back.


--Michael

[Michael Mair]

Re: Why is that?

Before I forget it:

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

#define newline "\n"

int main (void)
{
int var;
char *var2 = NULL;
ssize_t bytes_read = 0;
size_t nbytes = 0;


printf("Type a number: "); (void) fflush(stdout);
bytes_read = getline (&var2, &nbytes, stdin);
if(bytes_read == -1)
{
fprintf(stderr, "ERROR in line %d in return value from"
" getline()" newline, __LINE__);
(void) fflush(stderr);
exit(EXIT_FAILU RE);
}
if (sscanf(var2, "%d", &var) != 1)
{
fprintf(stderr, "ERROR in line %d: scanf() could not squeeze"
" a number out of your input" newline, __LINE__);
(void) fflush(stderr);
exit(EXIT_FAILU RE);
}
printf("The number is %d" newline, var);

printf("Type a string: "); (void) fflush(stdout);
bytes_read = getline (&var2, &nbytes, stdin);
if(bytes_read == -1)
{
fprintf(stderr, "ERROR in line %d in return value from"
" getline()" newline, __LINE__);
(void) fflush(stderr);
exit(EXIT_FAILU RE);
}

printf("The string is %s" newline, var2); (void) fflush(stdout);

free(var2);
exit(EXIT_SUCCE SS);
}


does the job for those of us with a new enough gcc compiler.

Your problem, of course, was the part I replaced by the
getline()/sscanf() pair.
Everyone else: Think fgets()/sscanf() and allocated buffer
var2.
As to the why: scanf() and family just do not empty the
input buffer as you seem to expect but get only what
they want. getline() found the leftover '\n' and that was
it. So, if you want to do it with scanf(), you will have
to empty the input buffer line with s.th. like

while ( (c=getchar()) != EOF )
if (c=='\n')
break;

(not tested)

Cheers
Michael

[Default User]

Re: Why is that?

Profetas wrote:[color=blue]
>
> I know what is causing the problem, but I couldn't
> find out why.[/color]


Which problem is that?



Brian Rodenborn

[Profetas]

Re: Why is that?

>>[color=blue][color=green]
>> I know what is causing the problem, but I couldn't
>> find out why.[/color][/color]

[color=blue]
>Which problem is that?[/color]

after the scanf is edxecuted it won't execute the getline

bash-2.05b$ ./a.out
Type a number:12
The number is 12
Type a string:The string is

[Profetas]

Re: Why is that?

>Your problem, of course, was the part I replaced by the[color=blue]
>getline()/sscanf() pair.
>Everyone else: Think fgets()/sscanf() and allocated buffer
>var2.
>As to the why: scanf() and family just do not empty the
>input buffer as you seem to expect but get only what
>they want. getline() found the leftover '\n' and that was
>it. So, if you want to do it with scanf(), you will have
>to empty the input buffer line with s.th. like[/color]

That is what I was looking for.

Thanks Michael Mair

[Default User]

Re: Why is that?

Profetas wrote:[color=blue]
>[color=green][color=darkred]
> >>
> >> I know what is causing the problem, but I couldn't
> >> find out why.[/color][/color]
>[color=green]
> >Which problem is that?[/color]
>
> after the scanf is edxecuted it won't execute the getline
>
> bash-2.05b$ ./a.out
> Type a number:12
> The number is 12
> Type a string:The string is[/color]

http://www.eskimo.com/~scs/C-faq/q12.18.html

Brian Rodenborn

[Jack Klein]

Re: Why is that?

On Wed, 18 Aug 2004 11:01:45 -0400, "Profetas" <xuxu_18@yahoo. com>
wrote in comp.lang.c:
[color=blue]
> I know what is causing the problem, but I couldn't
> find out why.[/color]

There is no version of standard C where this is a legal program.
[color=blue]
> main(){[/color]

The implicit int return type of main() is illegal from C99 onward.
[color=blue]
> int var;
> printf("Type a number:");[/color]

[snip]
[color=blue]
> char *var2;[/color]

Defining a variable after executable statements in a block is only
legal from C99 onward.

And as for these:
[color=blue]
> #define newline "\n"
> #define question_mark "\?"
> #define single_quotas "\'"
> #define double_quotas "\""
> #define form_feed "\f"
> #define horizontal_tab "\t"
> #define vertical_tab "\v"
> #define backslash "\\"[/color]

The standard doesn't allow it, but my opinion is that any program
written by anyone who writes macros this dumb should automatically
fail.

--
Jack Klein
Home: http://JK-Technology.Com
FAQs for
comp.lang.c http://www.eskimo.com/~scs/C-faq/top.html
comp.lang.c++ http://www.parashift.com/c++-faq-lite/
alt.comp.lang.l earn.c-c++

http://www.contrib.andrew.cmu.edu/~ajo/docs/FAQ-acllc.html

[Keith Thompson]

Re: Why is that?

Jack Klein <jackklein@spam cop.net> writes:[color=blue]
> On Wed, 18 Aug 2004 11:01:45 -0400, "Profetas" <xuxu_18@yahoo. com>
> wrote in comp.lang.c:[/color]
[...][color=blue]
> And as for these:
>[color=green]
> > #define newline "\n"[/color][/color]
[snip][color=blue]
> The standard doesn't allow it, but my opinion is that any program
> written by anyone who writes macros this dumb should automatically
> fail.[/color]

I think you meant "The standard *does* allow it...".

--
Keith Thompson (The_Other_Keit h) kst-u@mib.org <http://www.ghoti.net/~kst>
San Diego Supercomputer Center <*> <http://users.sdsc.edu/~kst>
We must do something. This is something. Therefore, we must do this.

[CBFalconer]

Re: Why is that?

Keith Thompson wrote:[color=blue]
> Jack Klein <jackklein@spam cop.net> writes:[color=green]
>> "Profetas" <xuxu_18@yahoo. com> wrote in comp.lang.c:[/color]
> [...][color=green]
>> And as for these:
>>[color=darkred]
>>> #define newline "\n"[/color][/color]
> [snip][color=green]
>> The standard doesn't allow it, but my opinion is that any program
>> written by anyone who writes macros this dumb should automatically
>> fail.[/color]
>
> I think you meant "The standard *does* allow it...".[/color]

I think he means the standard doesn't allow automatic failing of
extremely dumb programs.

--
Chuck F (cbfalconer@yah oo.com) (cbfalconer@wor ldnet.att.net)
Available for consulting/temporary embedded and systems.
<http://cbfalconer.home .att.net> USE worldnet address!

[Keith Thompson]

Re: Why is that?

CBFalconer <cbfalconer@yah oo.com> writes:[color=blue]
> Keith Thompson wrote:[color=green]
> > Jack Klein <jackklein@spam cop.net> writes:[color=darkred]
> >> "Profetas" <xuxu_18@yahoo. com> wrote in comp.lang.c:[/color]
> > [...][color=darkred]
> >> And as for these:
> >>
> >>> #define newline "\n"[/color]
> > [snip][color=darkred]
> >> The standard doesn't allow it, but my opinion is that any program
> >> written by anyone who writes macros this dumb should automatically
> >> fail.[/color]
> >
> > I think you meant "The standard *does* allow it...".[/color]
>
> I think he means the standard doesn't allow automatic failing of
> extremely dumb programs.[/color]

I think you're right. And so was he. And so am I (now).

--
Keith Thompson (The_Other_Keit h) kst-u@mib.org <http://www.ghoti.net/~kst>
San Diego Supercomputer Center <*> <http://users.sdsc.edu/~kst>
We must do something. This is something. Therefore, we must do this.

[Profetas]

Re: Why is that?

>The standard doesn't allow it, but my opinion is that any program[color=blue]
>written by anyone who writes macros this dumb should automatically[/color]
fail.

How do you know that it is dumb, if you don't even know the
rest of my program, and you don't know why it has been used
and its purpose, and how it has been written

don't judge what you don't know.

[Dan Pop]

Re: Why is that?

In <255f536db865d6 cb78f93f19c6fc0 5d2@localhost.t alkaboutprogram ming.com> "Profetas" <xuxu_18@yahoo. com> writes:
[color=blue][color=green]
>>The standard doesn't allow it, but my opinion is that any program
>>written by anyone who writes macros this dumb should automatically[/color]
>fail.
>
>How do you know that it is dumb, if you don't even know the
>rest of my program, and you don't know why it has been used
>and its purpose, and how it has been written[/color]

It is obvious, to anyone with a clue, that those macro definitions can
serve no good purpose in *any* C program.
[color=blue]
>don't judge what you don't know.[/color]

The judgment was entirely based on known things. Feel free to prove it
wrong by showing an example of good usage for those macros.

Here's an example of sensible macro:

#define SEPARATOR ','

and one of idiotic macro:

#define COMMA ','

The need to change the definition of SEPARATOR later in program's life is
conceivable, but there is no such need for a macro named COMMA.

Dan
--
Dan Pop
DESY Zeuthen, RZ group
Email: Dan.Pop@ifh.de

[Thomas Matthews]

Re: Why is that?

Profetas wrote:
[color=blue]
> I know what is causing the problem, but I couldn't
> find out why.
>
> #define newline "\n"
> #define question_mark "\?"
> #define single_quotas "\'"
> #define double_quotas "\""
> #define form_feed "\f"
> #define horizontal_tab "\t"
> #define vertical_tab "\v"
> #define backslash "\\"[/color]

One of the main problems of the above macros is
that you are using strings instead of characters.

If I have:
const char statement[] = "Hello\t\"World ?\"";
And I want to search for a "question_mark" ,
I would naturally want to use:
char * posn;
posn = strchr(statemen t, question_mark);
Which will not work because strchr() requires
a single char as the second parameter. Also,
this one will be hard to find:
posn = strchr(question _mark, statement);
In the above line, the first parameter has the
correct type, but wrong logic.

Also, please check your spelling. Note that
in English, "quota" and "quote" are two different
words. A quota is a limit. One could have a
single quota. There could also be double quotas,
which means having two limits; which is far from
the symbol (").

At some point, macros lead more to obfuscating
a program than to readablility.
If you want to keep down this path, may I also
suggest these macros:
#define begin {
#define end }
#ifndef and
#define and &&
#endif
#ifndef or
#define or ||
#endif
#ifndef not
#define not !
#endif
#define ever 1
#define forever 1

while (forever)
begin
if (a and b)
begin
continue;
end
else
begin
break;
end
end


--
Thomas Matthews

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[Christopher Benson-Manica]

Re: Why is that?

Profetas <xuxu_18@yahoo. com> spoke thus:
[color=blue]
> How do you know that it is dumb, if you don't even know the
> rest of my program, and you don't know why it has been used
> and its purpose, and how it has been written[/color]

Hang around here long enough and you'll realize that when certain
people (the eminent Mr. Klein being among them) call something you've
done "dumb", they're probably right. Lord knows it's happened to me
enough to know :)

--
Christopher Benson-Manica | I *should* know what I'm talking about - if I
ataru(at)cybers pace.org | don't, I need to know. Flames welcome.