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Reading a string of unknown size

I have to read characters from stdin and save them in a string. The
problem is that I don't know how much characters will be read.

Francesco
--
-------------------------------------

http://www.riscossione.info/
Nov 25 '06 #1
111 20024
Tonio Cartonio said:
I have to read characters from stdin and save them in a string. The
problem is that I don't know how much characters will be read.
http://www.cpax.org.uk/prg/writings/fgetdata.php
http://cbfalconer.home.att.net/download/ggets.zip
http://www.iedu.com/mrd/c/getsm.c
http://storm.freeshell.org/anysize.c

Take your pick.

(Coming soon - Eric Sosman's equivalent, if he can remember to attach it to
the email this time...)

--
Richard Heathfield
"Usenet is a strange place" - dmr 29/7/1999
http://www.cpax.org.uk
email: rjh at the above domain, - www.
Nov 25 '06 #2
Tonio Cartonio wrote:
I have to read characters from stdin and save them in a string. The
problem is that I don't know how much characters will be read.
You'll have to read the input, either character-at-a-time, (using
getc() or fgetc()), or line at a time, (using fgets()), and store them
into a block of memory which can be dynamically resized as you read in
more input.

It's fairly easy to do this yourself, but if you want to use an already
available one, try CBFalconer's ggets() function. Search the group's
archive. The URL is mentioned quite regularly.

Nov 25 '06 #3
I have to read characters from stdin and save them in a string. The
problem is that I don't know how much characters will be read.
int main()
{
char *str = NULL, ch ;
int i = 0 ;
str = (char*) malloc (2*sizeof(char) ) ;
*str = '\0' ;

while( (ch=getchar()) != '\n' )
{
*(str+i) = ch ;
i++ ;
str = (char*) realloc(str, (2*sizeof(char) ) + i ) ;
}
*(str+i) = '\0' ;

printf("\n\n %s ", str) ;

getch() ;
return 0;
}
:)
--
Regards
Santosh S Nayak
E-Mail - sa***********@g mail.com
WebPage -- http://santoshsnayak.googlepages.com

Nov 27 '06 #4
Santosh said:
>I have to read characters from stdin and save them in a string. The
problem is that I don't know how much characters will be read.

int main()
{
char *str = NULL, ch ;
int i = 0 ;
str = (char*) malloc (2*sizeof(char) ) ;
Here is your first bug.
*str = '\0' ;
Here's the second.
>
while( (ch=getchar()) != '\n' )
Here's the third.
{
*(str+i) = ch ;
i++ ;
str = (char*) realloc(str, (2*sizeof(char) ) + i ) ;
Here's the fourth and fifth, at least.
}
*(str+i) = '\0' ;

printf("\n\n %s ", str) ;
Here's your sixth.
>
getch() ;
And your seventh.
return 0;
}
:)
In fourteen lines of code (excluding spaces and braces), you managed at
least seven bugs. What are you smiling about?

--
Richard Heathfield
"Usenet is a strange place" - dmr 29/7/1999
http://www.cpax.org.uk
email: rjh at the above domain, - www.
Nov 27 '06 #5
:)In fourteen lines of code (excluding spaces and braces), you managed at
least seven bugs. What are you smiling about?
The program works correctly.

No offence pal, but make sure you are at least 10% right before you
reply to any post.

Nov 27 '06 #6
Santosh said:
:)In fourteen lines of code (excluding spaces and braces), you managed
:at
least seven bugs. What are you smiling about?

The program works correctly.
Really? Let's explore that, shall we?

foo.c:2: warning: function declaration isn't a prototype
foo.c: In function `main':
foo.c:3: `NULL' undeclared (first use in this function)
foo.c:3: (Each undeclared identifier is reported only once
foo.c:3: for each function it appears in.)
foo.c:5: warning: implicit declaration of function `malloc'
foo.c:5: warning: cast does not match function type
foo.c:8: warning: implicit declaration of function `getchar'
foo.c:12: warning: implicit declaration of function `realloc'
foo.c:12: warning: cast does not match function type
foo.c:16: warning: implicit declaration of function `printf'
foo.c:18: warning: implicit declaration of function `getch'
make: *** [foo.o] Error 1

Oh, look - it doesn't even compile.
No offence pal, but make sure you are at least 10% right before you
reply to any post.
I was 100% right that your program was a good 50% wrong (in terms of bugs
per line). And it doesn't compile on my system. If it compiles on yours
without generating at least one diagnostic message, then your compiler is
broken.

Furthermore, the OP did not indicate his platform (nor was there any need
for him to do that), let alone his implementation, so you can't just claim
"it works on *my* system", since there is no indication whatsoever that the
OP's system is the same as your system.

--
Richard Heathfield
"Usenet is a strange place" - dmr 29/7/1999
http://www.cpax.org.uk
email: rjh at the above domain, - www.
Nov 27 '06 #7
Santosh wrote:
I have to read characters from stdin and save them in a string. The
problem is that I don't know how much characters will be read.
First include necessary headers: stdio.h, stdlib.h
int main()
Better yet, replace above with int main(void)
{
char *str = NULL, ch ;
int i = 0 ;
str = (char*) malloc (2*sizeof(char) ) ;
Don't cast return value of malloc() in C. It can hide the non-inclusion
of it's prototype, (by way of failure to include stdlib.h), and, on
some implementations , can result in nasty crashes during runtime.

Since sizeof(char) is by definition 1, you can omit that and instead do
'2 * sizeof *str'. This has the advantage of becoming automatically
updated when you later on happen to change the type of *str.
*str = '\0' ;
And now you're possibly writing to a random area of memory, since you
failed to check the return value of malloc() above for failure.
while( (ch=getchar()) != '\n' )
Check for EOF not newline. Moreover getchar() returns an int value
which you're storing in a char variable, probably getting a spurious
garbage return value when end-of-file is encountered.
{
*(str+i) = ch ;
You've overwritten your earlier nul character.
i++ ;
str = (char*) realloc(str, (2*sizeof(char) ) + i ) ;
Again, _don't_ cast the return value of XXalloc() functions in C, and
check the call for failure before proceeding further. Also change
sizeof(char) to sizeof *str.

Anyway, your allocation strategy is very inefficient. Your calling
realloc() once every iteration of the loop. This could result in
fragmentation of the C library's memory pool. Why not allocate in terms
of fixed sized or dynamically growing blocks, say 128 bytes or so to
start with?
}
*(str+i) = '\0' ;

printf("\n\n %s ", str) ;
Unless you terminate the output with a newline character, it's not
guaranteed to show up on screen, or wherever stdout happens to be
directed to.
getch() ;
Non-standard, unportable and unnecessary function. Just get rid of it.

Nov 27 '06 #8
per line). And it doesn't compile on my system. If it compiles on yours
without generating at least one diagnostic message, then your compiler is
broken.

Furthermore, the OP did not indicate his platform (nor was there any need
for him to do that), let alone his implementation, so you can't just claim
"it works on *my* system", since there is no indication whatsoever that the
OP's system is the same as your system.
Do not get too excited and offensive, you forgot to include the
following files:
#include <stdio.h>
#include <conio.h>

If you are using a Unix system:
#include <stdio.h>
#include <sys/types.hOR #include <system.h>

Nov 27 '06 #9
Santosh said:
>per line). And it doesn't compile on my system. If it compiles on yours
without generating at least one diagnostic message, then your compiler is
broken.

Furthermore, the OP did not indicate his platform (nor was there any need
for him to do that), let alone his implementation, so you can't just
claim "it works on *my* system", since there is no indication whatsoever
that the OP's system is the same as your system.

Do not get too excited and offensive,
I am neither excited nor offensive.
you forgot to include the
following files:
#include <stdio.h>
#include <conio.h>
No, I didn't forget: you did.

And C offers no header named <conio.h>
If you are using a Unix system:
#include <stdio.h>
#include <sys/types.hOR #include <system.h>
Wrong. That wouldn't help your program compile.

Furthermore, even with the inclusion of those headers, your program is still
broken in several important ways.

I suggest you stop defending and start thinking.

The Other Santosh has given a good analysis of some of the problems with
your program. If you don't understand that analysis, start asking
intelligent questions instead of acting all defensively.

--
Richard Heathfield
"Usenet is a strange place" - dmr 29/7/1999
http://www.cpax.org.uk
email: rjh at the above domain, - www.
Nov 27 '06 #10

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