Re: problem in reading from file

From: Ed Morton (morton_at_lsupcaemnt.com)
Date: 09/26/05 

Date: Sun, 25 Sep 2005 17:35:42 -0500

hirenshah.05@gmail.com wrote:
> struct st{char ch[50];
> int n;
> }
>
> int main()
> {
> st *x,*y;
> int fd;
> scanf("%s\n%d",x.ch,x.n);
>
> fd=open("data",........)
> close(fd);
> fd=open("data",O_APPEND...)
> write(fd,&x,sizeof(st));
> close(fd);
> fd=open("data",...)
>
> // here i am facing problem. every time i run the program i am writing
> some data in file. but i want read data of whole file from start till
> end and display is on screen. but it is printing only entry added
> during program(i.e. last enrty).
> //
>
> while(read(fd,&y,sizeof(st)))
> {
> printf("%s%d",y->ch,y->n);
> }}
>

When you declare x and y like this:

        st *x,*y;

you're declaring POINTERS, not structures, so you don't have any memory
allocated to hold structures, so when you invoke scanf() and try to
populate the structures that you don't have, you're just writing to
random memory locations with unpredictable results. You're compiler is
almost certainly warning you about this. Fix this first, then see if
you're still having problems.

        Ed.

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