input a string in gcc

[yogicoder]

following is the code to accept a string from user, but i get
segmentation fault as soon i have finished entering the string i.e. as
soon as i press the 'enter' key.

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

int main (void)
{
char str[50];
printf ("Enter string:\n");
fgets (str, sizeof str, stdin);
//further code
}

if anybody can help me enter the string, thanx!

[Walter Roberson]

Re: input a string in gcc

In article <e53d3637-81f2-43d3-b5a9-df9db30998a9@f2 4g2000prh.googl egroups.com>,
yogicoder <zaperaj@gmail. comwrote:

>following is the code to accept a string from user, but i get
>segmentation fault as soon i have finished entering the string i.e. as
>soon as i press the 'enter' key.

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

>int main (void)
>{
> char str[50];
> printf ("Enter string:\n");
> fgets (str, sizeof str, stdin);

That part looks okay to me.

//further code
>}

You are not returning a value from main(), which leads to undefined
behaviour in C89/C90.

But I suspect the error is in the "//further code" part.
--
"Allegories are in the realm of thoughts, what ruins are in
the realm of things." -- Walter Benjamin

[Harald van =?UTF-8?b?RMSzaw==?=]

Re: input a string in gcc

On Sun, 08 Jun 2008 07:38:48 +0000, Walter Roberson wrote:

In article
<e53d3637-81f2-43d3-b5a9-df9db30998a9@f2 4g2000prh.googl egroups.com>,
yogicoder <zaperaj@gmail. comwrote:

>>following is the code to accept a string from user, but i get
>>segmentatio n fault as soon i have finished entering the string i.e. as
>>soon as i press the 'enter' key.

>

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

>

>>int main (void)
>>{
>> char str[50];
>> printf ("Enter string:\n");
>> fgets (str, sizeof str, stdin);

>
That part looks okay to me.
>

> //further code
>>}

>
You are not returning a value from main(),

If you treat //further code as just a comment, then you already know this
is not a C90 program. If you treat it as an indicator that there is more
code, that code may very well return a value from main().

which leads to undefined
behaviour in C89/C90.

No, it doesn't. It leads to an undefined return value, but not undefined
behaviour, in C90.

But I suspect the error is in the "//further code" part.

Agreed.

[Filipe Cabecinhas]

Re: input a string in gcc

yogicoder <zaperaj@gmail. comwrites:

following is the code to accept a string from user, but i get
segmentation fault as soon i have finished entering the string i.e. as
soon as i press the 'enter' key.

The error must be in the // further code part, as others have pointed
out. Compile your code with the -g flag and use valgrind or gdb to
see the offending line. After that try to fix it and, if you can't
(but TRY first) ask for help again.


--

- Filipe Cabecinhas

char* params[] = {"fil", "cab", "@", "gmail", ".", "com"};
puts("Real signature:");
for (int i = 0; i < sizeof(params)/sizeof(*params) ; ++i)
printf("%s", params[i]);
putchar('
');

[Richard Tobin]

Re: input a string in gcc

In article <e53d3637-81f2-43d3-b5a9-df9db30998a9@f2 4g2000prh.googl egroups.com>,
yogicoder <zaperaj@gmail. comwrote:

>following is the code to accept a string from user, but i get
>segmentation fault as soon i have finished entering the string i.e. as
>soon as i press the 'enter' key.

Does this very program get a segmentation fault, or only when you
put in the "further code"?

-- Richard
--
In the selection of the two characters immediately succeeding the numeral 9,
consideration shall be given to their replacement by the graphics 10 and 11 to
facilitate the adoption of the code in the sterling monetary area. (X3.4-1963)

[Bartc]

Re: input a string in gcc


"yogicoder" <zaperaj@gmail. comwrote in message
news:e53d3637-81f2-43d3-b5a9-df9db30998a9@f2 4g2000prh.googl egroups.com...

following is the code to accept a string from user, but i get
segmentation fault as soon i have finished entering the string i.e. as
soon as i press the 'enter' key.

How soon exactly? Enough time for your computer to execute a hundred million
lines of code following the fgets perhaps?

If you put in a printf or puts statement just before your '//further code'
you can establish whether the problem is with the fgets, or with the
'further code'.

--
Bartc

[Richard]

Re: input a string in gcc

yogicoder <zaperaj@gmail. comwrites:

following is the code to accept a string from user, but i get
segmentation fault as soon i have finished entering the string i.e. as
soon as i press the 'enter' key.
>

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
>
int main (void)
{
	char str[50];
	printf ("Enter string:\n");
	fgets (str, sizeof str, stdin);
        //further code
}

>
if anybody can help me enter the string, thanx!

use a debugger and find where it happens.

[yogicoder]

Re: input a string in gcc

On Jun 8, 4:10 pm, "Bartc" <b...@freeuk.co mwrote:

"yogicoder" <zape...@gmail. comwrote in message
>
news:e53d3637-81f2-43d3-b5a9-df9db30998a9@f2 4g2000prh.googl egroups.com...
>

following is the code to accept a string from user, but i get
segmentation fault as soon i have finished entering the string i.e. as
soon as i press the 'enter' key.

>
How soon exactly? Enough time for your computer to execute a hundred million
lines of code following the fgets perhaps?
>
If you put in a printf or puts statement just before your '//further code'
you can establish whether the problem is with the fgets, or with the
'further code'.
>
--
Bartc

Well i didn't consider further code important because i had already
used a printf("test") statement immediately after fgets & it's not
getting executed. I get seg fault eror the instant i hit the enter
key.

[Joe Wright]

Re: input a string in gcc

yogicoder wrote:

On Jun 8, 4:10 pm, "Bartc" <b...@freeuk.co mwrote:

>"yogicoder" <zape...@gmail. comwrote in message
>>
>news:e53d363 7-81f2-43d3-b5a9-df9db30998a9@f2 4g2000prh.googl egroups.com...
>>

>>following is the code to accept a string from user, but i get
>>segmentatio n fault as soon i have finished entering the string i.e. as
>>soon as i press the 'enter' key.

>How soon exactly? Enough time for your computer to execute a hundred million
>lines of code following the fgets perhaps?
>>
>If you put in a printf or puts statement just before your '//further code'
>you can establish whether the problem is with the fgets, or with the
>'further code'.
>>
>--
>Bartc

>
Well i didn't consider further code important because i had already
used a printf("test") statement immediately after fgets & it's not
getting executed. I get seg fault eror the instant i hit the enter
key.

There must be something else going on. The following works fine here.

#include <stdio.h>

int main(void)
{
char str[50];
printf("Enter string:\n");
fgets(str, sizeof str, stdin);
fputs(str, stdout);
return 0;
}


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

[Bartc]

Re: input a string in gcc


"yogicoder" <zaperaj@gmail. comwrote in message
news:c4d253ec-5885-48b8-a6f3-b992f9010699@u6 g2000prc.google groups.com...

On Jun 8, 4:10 pm, "Bartc" <b...@freeuk.co mwrote:

>"yogicoder" <zape...@gmail. comwrote in message
>>
>news:e53d363 7-81f2-43d3-b5a9-df9db30998a9@f2 4g2000prh.googl egroups.com...
>>

following is the code to accept a string from user, but i get
segmentation fault as soon i have finished entering the string i.e. as
soon as i press the 'enter' key.

>>
>How soon exactly? Enough time for your computer to execute a hundred
>million
>lines of code following the fgets perhaps?
>>
>If you put in a printf or puts statement just before your '//further
>code'
>you can establish whether the problem is with the fgets, or with the
>'further code'.
>>
>--
>Bartc

>
Well i didn't consider further code important because i had already
used a printf("test") statement immediately after fgets & it's not
getting executed. I get seg fault eror the instant i hit the enter
key.

Thanks, that's useful clarification. So in this program (I've added \n to
the printf):

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

int main (void)
{
char str[50];
printf ("Enter string:\n");
fgets (str, sizeof str, stdin);
printf("test\n" );
}

after you hit Enter (for test purposes, don't type anything else), it does
not print "test"? I'm asking because on my machine (and I suspect many
others) it works as expected.

What happens if you comment out the fgets line?

--
Bartc

[Richard]

Re: input a string in gcc

"Bartc" <bc@freeuk.comw rites:

"yogicoder" <zaperaj@gmail. comwrote in message
news:c4d253ec-5885-48b8-a6f3-b992f9010699@u6 g2000prc.google groups.com...

>On Jun 8, 4:10 pm, "Bartc" <b...@freeuk.co mwrote:

>>"yogicoder" <zape...@gmail. comwrote in message
>>>
>>news:e53d36 37-81f2-43d3-b5a9-df9db30998a9@f2 4g2000prh.googl egroups.com...
>>>
>following is the code to accept a string from user, but i get
>segmentation fault as soon i have finished entering the string i.e. as
>soon as i press the 'enter' key.
>>>
>>How soon exactly? Enough time for your computer to execute a hundred
>>million
>>lines of code following the fgets perhaps?
>>>
>>If you put in a printf or puts statement just before your '//further
>>code'
>>you can establish whether the problem is with the fgets, or with the
>>'further code'.
>>>
>>--
>>Bartc

>>
>Well i didn't consider further code important because i had already
>used a printf("test") statement immediately after fgets & it's not
>getting executed. I get seg fault eror the instant i hit the enter
>key.

>
Thanks, that's useful clarification. So in this program (I've added \n to
the printf):
>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
>
int main (void)
{
char str[50];
printf ("Enter string:\n");
fgets (str, sizeof str, stdin);
printf("test\n" );
}
>
after you hit Enter (for test purposes, don't type anything else), it does
not print "test"? I'm asking because on my machine (and I suspect many
others) it works as expected.
>
What happens if you comment out the fgets line?

use a debugger. get a backtrace.

[Filipe Cabecinhas]

Re: input a string in gcc

yogicoder <zaperaj@gmail. comwrites:

Well i didn't consider further code important because i had already
used a printf("test") statement immediately after fgets & it's not
getting executed. I get seg fault eror the instant i hit the enter
key.

Install valgrind, run your program with: valgrind ./prog
then show us the errors.

--

- Filipe Cabecinhas

char* params[] = {"fil", "cab", "@", "gmail", ".", "com"};
puts("Real signature:");
for (int i = 0; i < sizeof(params)/sizeof(*params) ; ++i)
printf("%s", params[i]);
putchar('\n');

[Richard Tobin]

Re: input a string in gcc

In article <c4d253ec-5885-48b8-a6f3-b992f9010699@u6 g2000prc.google groups.com>,
yogicoder <zaperaj@gmail. comwrote:

>Well i didn't consider further code important because i had already
>used a printf("test") statement immediately after fgets & it's not
>getting executed. I get seg fault eror the instant i hit the enter
>key.

When you're asking other people to help fix your code, it's not a good
idea to rely on what *you* think is important. After all, if you knew
what was important you'd be able to find the bug yourself.

How do you know the printf("test") statement is not being executed?
Do you really mean that "test" isn't being printed? Normally terminal
output is line-buffered, so it won't get printed until you output
a newline.

If you want help, send a complete program that fails, not a cut-down
program that you haven't tested.

-- Richard
--
In the selection of the two characters immediately succeeding the numeral 9,
consideration shall be given to their replacement by the graphics 10 and 11 to
facilitate the adoption of the code in the sterling monetary area. (X3.4-1963)

[pete]

Re: input a string in gcc

Richard Tobin wrote:

In article <c4d253ec-5885-48b8-a6f3-b992f9010699@u6 g2000prc.google groups.com>,
yogicoder <zaperaj@gmail. comwrote:
>

>Well i didn't consider further code important because i had already
>used a printf("test") statement immediately after fgets & it's not
>getting executed. I get seg fault eror the instant i hit the enter
>key.

>
When you're asking other people to help fix your code, it's not a good
idea to rely on what *you* think is important. After all, if you knew
what was important you'd be able to find the bug yourself.

Anytime somebody introduces a debugging problem
by saying where the problem isn't,
that's where I look first.

--
pete

[yogicoder]

Re: input a string in gcc

On Jun 8, 7:17 pm, pete <pfil...@mindsp ring.comwrote:

Richard Tobin wrote:

In article <c4d253ec-5885-48b8-a6f3-b992f9010...@u6 g2000prc.google groups.com>,
yogicoder <zape...@gmail. comwrote:

>

Well i didn't consider further code important because i had already
used a printf("test") statement immediately after fgets & it's not
getting executed. I get seg fault eror the instant i hit the enter
key.

>

When you're asking other people to help fix your code, it's not a good
idea to rely on what *you* think is important. After all, if you knew
what was important you'd be able to find the bug yourself.

>
Anytime somebody introduces a debugging problem
by saying where the problem isn't,
that's where I look first.
>
--
pete

well yes people you all were right. There is some error in the code
after fgets. What was happening was that the printf immediately after
fgets was also not getting executed because of some error further away
in my code. This was my first post so please don't castigate me for
this.
So here's a detailed explanation:
Basically what my code is supposed to do is accept a string from user
& reverse the position of the words, for e.g.
Input: this is a string
Output: string a is this
I have to do this in O(n) complexity.
Here's my code :
[CODE]
#include <stdio.h>
#include <string.h>
#include <stdlib.h>

int main (void)
{

void change (char []);
char str[50];
printf ("Enter string:\n");
fgets (str, sizeof str, stdin);
change (str);
printf ("\nRequired string is:\n");
fputs (str, stdout);
return 0;
}

void change (char str[50])
{
char *arr[20], *a;
int i, j, k;
i = j = 0;
while (str[j] != '\n') {
*arr[i] = str[j];
if (str[j] == ' ')
++i;
str[++j];
arr[i]++;
}
*arr[i] = '\0';
k = j = i;
i = 0;
while (i < j) {
a = arr[i];
arr[i] = arr[j];
arr[j] = a;
++i;
--j;
}
i = j = 0;
while (*arr[i] != '\0') {
str[j] = *arr[i];
if (*arr[i] == ' ')
++i;
str[++j];
arr[i]++;
}
str[j] = *arr[i];
return;
}

There's some error with pointers i know, but i am not able to
understand it. You guys have really been helpful so thanks a lot! I've
spent a lot of time on this so help would be greatly appreciated.