Re: [Dev-C++] Problems with input

[Per W. <pw...@ia...>]

I really don't understand your talk about malloc() and checking for
sucessful allocation here.

If doing
  char str = (char*)malloc(10);
then the allocation may fail, the the application should test:
  if (str == NULL) fail;
or
  if (!str) fail;

However, when declaring:
  char str[10];
then the only way the application can fail is if the operating system
can't supply enough stack space. There are no pointer to test. If the
allocation fails (the stack can't fit the variable) then the application
will die.


However, you are correct that gets() should not be used. Or more strongly:
SHOULD NEVER BE USED. If doing C-style input, the function to use is
fgets() since it takes an extra parameter to inform about the size of the
input buffer. gets() is one of the hacker dream functions. If gets() is
used, then the application is compromised.

/pwm

On Mon, 16 Jul 2007, Adam Jones wrote:

> >>Hello,
>
> >>I have got a problem I don't understand very much.
>
> >>I have in my code:
>
> >>#include<stdio.h>
> >>int main()
> >>{
> >>char str[10];
>
> >>getchar ();
> >>gets (str);
> >>printf ("%s\n", str);
> >>return 0;
> >>}
>
> It would be helpful to all of us if you could explain why you feel it
> necessary to use getchar() the gets() the way you do. What are you trying to
> accomplish by doing it this way.
> getchar() waits for any keypress to continue, and gets will wait until it
> encounters the newline or end of file before continuing.
>
> You also have a potential to corrupt memory here. What happens if the person
> enters a string longer than 10 Char.  You also assume which is not very good
> that the system will allocate a char str[10] without checking to see if it
> can do it with a malloc first. On memory allocations you need to check
> first, and if it fails exit your program gracefully.
>
> >>In this case it seems the program is ignoring the "gets ()" command. After
> I press some key and >CR>It stops and doesn't wait for line input.  If I do
> not have there the "getchar () I >>can input a line.
>
> If you hit any key and the CR then the single key press goes to getchar()
> the <CR> goes to the gets() which terminates that call. You should just hit
> any key, then type in your string and then hit CR when you are done. The
> getchar() does not require you to hit CR in order for it to accept the key
> press. This should work.
>
> -Adam Jones
>
>
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