char pointers in C

Code:

---


#include<stdio.h>
#include<conio.h>
main()
{
int i;
char *s;
scanf("%s",&s);
printf("%s",s);
getch();
}

---

i ran this code on dev c++ in windows xp...
xp shows a error:
" ....has encountered a problem and needs to close.
We are sorry for the inconvenience."

why does this happen??
and how to receive char pointers as input??

Quote:

---

Originally Posted by Rishi Kumar

Code:

---


#include<stdio.h>
#include<conio.h>
main()
{
int i;
char *s;
scanf("%s",&s);
printf("%s",s);
getch();
}

---

i ran this code on dev c++ in windows xp...
xp shows a error:
" ....has encountered a problem and needs to close.
We are sorry for the inconvenience."

why does this happen??
and how to receive char pointers as input??

---

You have to allocate memory for 's' either at initialization or at runtime using malloc.
Also,No ampersand for scanf since string is the input.

i am a beginner.... i have never used malloc be4... how to use it...
this program works perfectly in turbo c 2.01....
(removing "&" makes no difference)...

http://cpwiki.sf.net/A_pointer_on_pointers
If that doesn't make sense, you have to go back to the book.
Also note that scanf is dangerous: http://cpwiki.sf.net/Buffer_overrun
And implicit main is bad: http://cpwiki.sf.net/Implicit_main

And if you don't know how malloc works, then maybe it's back to the book again. C is not an easy language. Make sure you properly understand what the functions do before you use them.

Like this:
with malloc:

Code:

---

#include<stdio.h>
#include<stdlib.h>
int main()
{
    int i;
    char *s;
    s=(char *)malloc(10);
    scanf("&#37;s",s);
    printf("%s",s);

    return 0;
}

---

or
without malloc:

Code:

---

#include<stdio.h>
#include<stdlib.h>
int main()
{
    int i;
    char s[10];
    scanf("%s",s);
    printf("%s",s);

    return 0;
}

---

Do not cast the return of malloc.
Do not read strings with scanf without specifying buffer size.
FREE the memory after you're done with it.
(Read links!)

Are char pointers an alternative to strings...???

Thanks for the inputs Elysia.
I'll try my best to improve my coding.
If I do not cast malloc I get the Following error:

error: invalid conversion from `void*' to `char*'

Can you please explain how to do it.

Quote:

---

Originally Posted by Rishi Kumar

Are char pointers an alternative to strings...???

---

No, they are not. Char pointers can be used, and are frequently used, as strings, but they are not strings (they are a pointer to somewhere in memory that typically contains a character array).
You seem to lack basic understanding of how C works. Do you have a book?

Quote:

---

Originally Posted by stevesmithx

Thanks for the inputs Elysia.
I'll try my best to improve my coding.

---

Good luck :)

Quote:

---

If I do not cast malloc I get the Following error:

error: invalid conversion from `void*' to `char*'

---

You are probably compiling the code in a C++ compiler. In C, the recommended practice is not to have that cast, but in C++, a cast is necessary.

i dont have a fixed book for studying c...
i refer to tutorials and books then n thr...
any really gud somewat complicated book u wud recommend??

Quote:

---

Originally Posted by stevesmithx

If I do not cast malloc I get the Following error:
error: invalid conversion from `void*' to `char*'
Can you please explain how to do it.

---

If using C++, then you must cast the result as laserlight points out.
But be careful not to suggest it to other people who use C, because with a C compiler, it's a very bad thing(TM).

Quote:

---

Originally Posted by Rishi Kumar

i dont have a fixed book for studying c...
i refer to tutorials and books then n thr...
any really gud somewat complicated book u wud recommend??

---

See the recommended books thread on the forum.

Thank you laserlight and Elysia.

I am using Code::Blocks IDE with GCC compiler.

Still I am getting this error.

Since you are compiling C in C++, it must be:
char* s = (char*)malloc(10);
(Note the cast.)

Quote:

---

I am using Code::Blocks IDE with GCC compiler.

Still I am getting this error.

---

Make sure that your file extension is .c, not .cpp, .cxx, .cc or .C (etc).

thanx Elysia...

i dont get any error with fgets...
i use dev c++ with gcc compiler...
but i get a warning: "passing arg 1 of `fgets' from incompatible pointer type"... y???

What's so bad about casting malloc in C? Wouldnt it be better because it will be easier to transfer your C code to C++?

Thank you laserlight.
I had saved it as .C
For .c it works.
And I thought extensions are not case sensitive.
Thanks all

Quote:

---

What's so bad about casting malloc in C? Wouldnt it be better because it will be easier to transfer your C code to C++?

---

read casting malloc.

Quote:

---

Originally Posted by Rishi Kumar

thanx Elysia...

i dont get any error with fgets...
i use dev c++ with gcc compiler...
but i get a warning: "passing arg 1 of `fgets' from incompatible pointer type"... y???

---

It means that you are trying to pass an argument to a function that expects a pointer of a certain type, but you are passing another type of pointer.
If we could see the fgets code, maybe we could help.

Example:

Code:

---

int x;
fgets(&x, 1, 1, f); /* passing arg 1 of `fgets' from incompatible pointer type */

---

(fgets is expecting char*, not int*)

Quote:

---

Originally Posted by 39ster

What's so bad about casting malloc in C?

---

Because of implicit function calls are masked (in case you forgot to include the header where malloc's prototype resides). See the FAQ for more details.

Quote:

---

Originally Posted by 39ster

Wouldnt it be better because it will be easier to transfer your C code to C++?

---

I certainly do agree with you there. I like to call it C++/C :D C code compiled with C++.
But we can't force anyone.

Code:

---

#include<stdio.h>
#include<conio.h>
main()
{
char *s[10];
fgets(s, 10, stdin);
printf("&#37;s",s);
getch();
}

---

it shows a warning...
" passing arg 1 of `fgets' from incompatible pointer type "

i accept only char* as input...

In your new code example, s is an array of 10 char pointers. What you want is:

Code:

---

#include<stdio.h>

int main()
{
    char s[10];
    fgets(s, 10, stdin);
    printf("&#37;s",s);
    return 0;
}

---

Try reading the link for implicit main and get rid of it.
The problem is

Code:

---

char* s[10];

---

Which creates an array of 10 char pointers.
Thus passing this to fgets will result in char**.
Futher, the array has no allocates storage so you'd get a crash immediately.

And it's better to use getchar() instead of getch() (it's non-standard).