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Re: [Dev-C++] (no subject)
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From: Per W. <pw...@ia...> - 2003-07-03 20:15:30
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Sorry for coming out a bit rough but it's just that I think this issues
are important. Too many programs fails miserably because of this kind of
errors.
First of all - count the number of parameters used to
sprintf(temp,"\r\n","");
What would you say the third parameter was used for. Sending extra
parameters just because a variadric function allows it MUST be called
inefficient.
Second - do you notice any formatting character in the second parameter?
If not, then there is no need to call sprintf(), and strcpy() would
clearly be preferable to use.
Third - why talk about how expensive a line is, when - in reality - it
isn't needed at all. You might notice that
WriteFile(handle,"\r\n",2,&dwCount,NULL);
doesn't need the text to becopied to a temporary buffer before it is
emitted. Also, 2 is the correct number of characters to emit if the goal
is to generate a normal text file - at least until we aim for Unicode or
multi-byte encodings.
I'm pretty sure that temp wasn't declared as:
char temp[2]
so sizeof(temp) will most certainly result in an incorrect number of
characters being written.
Notice that
sprintf(temp,"\r\n");
would require 3 characters in temp, while
sprintf(temp,"%3d",x);
would require at least 4 - depending on the value of x.
Obviously, it isn't possible to emit the two strings to a text file
by using sizeof(temp). It wasn't possible in the original question either,
since sprintf() requires room an extra termination chaarcter. Either
temp[] would be large enough for that character - but then the termination
character would also be emitted. Or temp[] was just large enough for the
characters, but then sprintf() would have made a buffer overflow.
But still - the code didn't prove that -99 <= ran1[loop] <= 999. Without
that assumption, it isn't possible to predict the number of charactesr
that sprintf() needs when performing the %3d processing. Given a variable
number of characters in the formatted string, sizeof(temp) may never work,
and strlen(temp) must be used.
If emitting a binary file, sizeof(temp) is ok, since then temp[] might be
defined "large enough", and the program may safely ignore any random
characters emitted after the '\0' string termination and the full size of
the temp[] buffer. However, the use of "\r\n" in the output seems like a
very large indication that a binary fixed record-size file was intended.
/Per W
On Thu, 3 Jul 2003, Daniel Glenfield wrote:
> Given the speed of processors now, something like that can hardly be called
> expensive can it?
>
>
> >From: Per Westermark <pw...@ia...>
> >To: Daniel Glenfield <sp...@ho...>
> >CC: jab...@ma...,
> ><dev...@li...>
> >Subject: Re: [Dev-C++] (no subject)
> >Date: Thu, 3 Jul 2003 19:17:12 +0200 (CEST)
> >
> >But that ignores the problem that sizeof(temp) doesn't take into account
> >the number of characters in the buffer, only total declared size of it. As
> >such, sizeof(temp) should never be used for emitting text files unless you
> >really, really, really - did I say really? - know what you are doing.
> >strlen() is available specifically for checking the length of a string.
> >
> >In the first WriteFile() call, temp contains 2 characters, a terminating
> >zero and an unknown number of extra garbage at the end - depending on what
> >size it was declared as.
> >
> >In the second WriteFile() call, temp constans 3 characters, a terminating
> >zero and an unknown number of extra garbage.
> >
> >Besides, sprintf(temp,"\r\n","") is a bit expensive since the formatting
> >string didn't contain any formatting. That is when strcpy(temp,"\r\n")
> >should be used.
> >
> >Further, since the emitted string is a constant, why not directly emit
> >WriteFile(hFile,"\r\n",2,&dWritten,NULL);
> >
> >Any why not check the return value and the value of dWritten? And - just
> >a bit more knit-picking - dWritten should be called dwWritten since it is
> >of type double-word.
> >
> >/Per W
> >
> >On Thu, 3 Jul 2003, Daniel Glenfield wrote:
> >
> > > Hey you guys hear that? I was correct!!! Ha ha! This feels great!
> > >
> > > Cheers,
> > > Daniel
> > >
> > > >From: "Jorge Abramian" <jab...@ma...>
> > > >Reply-To: <jab...@ma...>
> > > >To: <dev...@li...>
> > > >Subject: [Dev-C++] (no subject)
> > > >Date: Thu, 3 Jul 2003 09:47:14 -0400
> > > >
> > > >Hey guys, thanks for the help,
> > > >
> > > >Actually Daniel Glenfield was write. I did not try Per W. solution that
> > > >probably would work either.
> > > >
> > > >I changed the code to the followin and it worked well:
> > > >
> > > >/////////
> > > > for (loop=0;loop<Number_of_Points;loop++)
> > > > {
> > > > DWORD dWritten;
> > > > sprintf (temp,"\r\n","");
> > > > WriteFile(hFile, temp, sizeof(temp),&dWritten, NULL);
> > > > sprintf (temp,"%3d",ran1[loop]);
> > > > WriteFile(hFile, temp, sizeof(temp),&dWritten, NULL);
> > > > }
> > > >/////////
> > > >
> > > >
> > > >
> > > >
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