Problem using fseek

[Maria Mela]

Hello everyone...

I´ve a problem with my code, when i put this lines:

recsize = sizeof(p1);
fseek(fp,-recsize,SEEK_CU R); fwrite(&p1,size of(p1),1,fp);
getch();

The file was saved with correct values and with some windows informations
too!?

like this " 8 
O r i g i n a l F i l e n a m e C m d . E x e l &
P
r o d u c t N a m e"

what are the problem?!

Kisses

[user923005]

On Feb 6, 2:50 pm, "Maria Mela" <h...@netvisao. ptwrote:

Hello everyone...

I´ve a problem with my code, when i put this lines:

recsize = sizeof(p1);
fseek(fp,-recsize,SEEK_CU R); fwrite(&p1,size of(p1),1,fp);
getch();

The file was saved with correct values and with some windows informations
too!?

like this " 8 O r i g i n a l F i l e n a m e C m d . E x e l & P
r o d u c t N a m e"

what are the problem?!

Show the actual code you are using and not a snippet of it.
Simplify the code until you have the minimal fully working code that
demonstrates the problem.

As a wild guess, you might be trying to read an OLE compound document
using fread, which is destined to humor.

[Jeffrey Stedfast]

user923005 wrote:

On Feb 6, 2:50 pm, "Maria Mela" <h...@netvisao. ptwrote:

>Hello everyone...

I´ve a problem with my code, when i put this lines:

recsize = sizeof(p1);
fseek(fp,-recsize,SEEK_CU R); fwrite(&p1,size of(p1),1,fp);
getch();

The file was saved with correct values and with some windows informations
too!?

like this " 8 O r i g i n a l F i l e n a m e C m d . E x e l & P
r o d u c t N a m e"

what are the problem?!

Show the actual code you are using and not a snippet of it.
Simplify the code until you have the minimal fully working code that
demonstrates the problem.

As a wild guess, you might be trying to read an OLE compound document
using fread, which is destined to humor.

or p1 points to a struct with pointers... fwrite() obviously won't
serialise string pointers in a struct.

maybe also byte padding? who knows.

[Maria Mela]

here´s my struct

struct customer {
int dd,mm,yy;
char cus_ac_no[15],cus_name[25],cus_add[45],cus_ph_no[17];
double cus_bal;
float cus_intrst;
}p1;

typedef struct customer cust;

FILE *fp,*ft;
int recsize;
char choice,any,ch,e no[23];
double dep,
void transac()//Transaccoes de um Cartao
{
int k,p,t,r;
system("cls");
k=valid();
rewind(fp);
if(k!=2)
{
// _setcursortype( _NOCURSOR);
calbox(); highvideo();
gotoxy(12,12); cprintf(" N£mero invalido! ");
gotoxy(19,14); cprintf(" Tente Novamente");
getch();
}
else
{
while(fread(&p1 ,sizeof(p1),1,f p)==1)
{
if(strcmp(p1.cu s_ac_no,eno)==0 )
{
calbox();
fflush(stdin);
choice=getchar( );
switch(choice)
{
/*-----------------------------------------------------*/
case '1':
calbox();
gotoxy(5,5); cprintf("xxxxxx :");
gotoxy(8,7);cpr intf("Euros :");
scanf("%lf",&de p);
p1.cus_bal+=dep ;
acc_info(&p1);
recsize = sizeof(p1);
fseek(fp,-recsize,SEEK_CU R); fwrite(&p1,size of(p1),1,fp);
getch();
break;
"user923005 " <dc*****@connx. comescreveu na mensagem
news:11******** **************@ v45g2000cwv.goo glegroups.com.. .
On Feb 6, 2:50 pm, "Maria Mela" <h...@netvisao. ptwrote:

Hello everyone...

I´ve a problem with my code, when i put this lines:

recsize = sizeof(p1);
fseek(fp,-recsize,SEEK_CU R); fwrite(&p1,size of(p1),1,fp);
getch();

The file was saved with correct values and with some windows informations
too!?

like this " 8 O r i g i n a l F i l e n a m e C m d . E x e l &
P
r o d u c t N a m e"

what are the problem?!

Show the actual code you are using and not a snippet of it.
Simplify the code until you have the minimal fully working code that
demonstrates the problem.

As a wild guess, you might be trying to read an OLE compound document
using fread, which is destined to humor.

[user923005]

You missed this bit:
" minimal fully working code "
Which means that it should at least compile and run and demonstrate
the problem.

I suspect you might have a problem with uninitialized data, or struct
alignment (if two different machines read and write the information)
but there is no way to know with what we have been given so far.

Since you are using non-standard Borland functions, it will probably
take a bit longer to get the answers because we will have to stub
those out.

[CBFalconer]

Maria Mela wrote:

>

.... snip ...

>
fflush(stdin);
choice=getchar( );
switch(choice)
{
/*-----------------------------------------------------*/
case '1':
calbox();
gotoxy(5,5); cprintf("xxxxxx :");
gotoxy(8,7);cpr intf("Euros :");
scanf("%lf",&de p);

Why should anyone bother to analyze something that is not
compilable (no main, no #includes) and is obviously in error
(fflush does not function on stdin, no such functions as gotoxy,
cprintf) etc.

Post complete, compilable code, with non-standard garbage
eliminated, after cutting it down to 100 lines or less. By the
time you do that you will probably find the fault yourself. If you
don't know what is standard and what isn't, say so and the
non-portable non-standardisms will be rapidly pointed out to you by
the howling mob.

If you want help, make it easy for someone to help you.

--
<http://www.cs.auckland .ac.nz/~pgut001/pubs/vista_cost.txt>
<http://www.securityfoc us.com/columnists/423>

"A man who is right every time is not likely to do very much."
-- Francis Crick, co-discover of DNA
"There is nothing more amazing than stupidity in action."
-- Thomas Matthews

[Beej]

On Feb 6, 5:35 pm, CBFalconer <cbfalco...@yah oo.comwrote:

fflush does not function on stdin

That language is a little strong. fflush(stdin) clears the input
buffer on some systems, but one should know that it's not portable.

-Beej

[Keith Thompson]

"Beej" <be**@beej.uswr ites:

On Feb 6, 5:35 pm, CBFalconer <cbfalco...@yah oo.comwrote:

>fflush does not function on stdin

That language is a little strong. fflush(stdin) clears the input
buffer on some systems, but one should know that it's not portable.

And that's a little weak. Passing a pointer to an input stream (such
as stdin) to fflush() invokes undefined behavior. Some
implementations may choose to define the behavior.

--
Keith Thompson (The_Other_Keit h) ks***@mib.org <http://www.ghoti.net/~kst>
San Diego Supercomputer Center <* <http://users.sdsc.edu/~kst>
We must do something. This is something. Therefore, we must do this.

[Richard Heathfield]

Beej said:

On Feb 6, 5:35 pm, CBFalconer <cbfalco...@yah oo.comwrote:

>fflush does not function on stdin

That language is a little strong.

More precisely, the behaviour of fflush on input streams is undefined.

fflush(stdin) clears the input
buffer on some systems, but one should know that it's not portable.

And indeed there is no reason to risk it, since portable alternatives
exist, and are trivial to code.

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

[Keith Thompson]

Richard Heathfield <rj*@see.sig.in validwrites:

Beej said:

>On Feb 6, 5:35 pm, CBFalconer <cbfalco...@yah oo.comwrote:

>>fflush does not function on stdin

That language is a little strong.

More precisely, the behaviour of fflush on input streams is undefined.

>fflush(stdin ) clears the input
buffer on some systems, but one should know that it's not portable.

And indeed there is no reason to risk it, since portable alternatives
exist, and are trivial to code.

That's not quite true, depending on what "input buffer" is being
cleared. For example, if input is from a keyboard, it might be useful
to zero the typeahead buffer, in case the user incorrectly anticipated
what the prompt was going to be:

The program prompts "Enter user name: "

The user types "fred" followed by a newline.

The system is being a bit sluggish. The user assumes that the
next prompt is going to be "Enter password: " and types "qLutGg8A"
followed by a newline.

The program was recently modified so a password isn't required,
and the next prompt is actually "Enter broadcast message: ".

Fred's password is now sent out to everybody on the system.

If a call to fflush(stdin) were done before the "Enter broadcast
message: " prompt was issued, *and* if this call discarded the
password characters, then this problem might be avoided. I've used
similar facilities in the past, but not in C. I don't know whether
fflush(stdin) actually works this way on any of the systems that
support it.

This is different from reading and discarding all input up to the next
newline, which is often all you really need.

But the fact remains, fflush(stdin) invokes undefined behavior, and
any code that depends on the behavior of an implementation that
chooses to define it is non-portable, perhaps dangerously so.

(BTW, don't bother guessing what "qLutGg8A" is. It's randomly
generated; I've never used it as a password, and I never will.)

--
Keith Thompson (The_Other_Keit h) ks***@mib.org <http://www.ghoti.net/~kst>
San Diego Supercomputer Center <* <http://users.sdsc.edu/~kst>
We must do something. This is something. Therefore, we must do this.