Loop Iterations Counter; Does It Exist?

[drmario]

Here's what I got:

ifstream File; // already initialized and associated with a file
input stream
unsigned short r = 1; // a counter to tell me if this is the loop's first
iteration

do {
if( (File.peek() == 32) && r)
return 0;
else if ... snip
else ... snip
r=0;
} while(some condition)

I've done this because I want to know if my function encounters the newline
character before everything else. If it does, I need it to return false.
If it doesn't, I need it to make r=0, so that on the next iteration if it
happens to find a newline char, but it's not the first iteration, it won't
return false.

What I don't like is that let's say 100 iterations of this loop happens
before it returns anything. I'm wasting processor time by assigning 0 to r
every single iteration.

Therefore my question is: is there not a way for me to change that if ( )
statement up there so that I can somehow see if this is the first iteration
of the do...while() loop, WITHOUT having to use a variable and waste
processor time assigning it all the time?

thanks
Mario

[Kai-Uwe Bux]

drmario wrote:

Here's what I got:

ifstream File; // already initialized and associated with a file
input stream
unsigned short r = 1; // a counter to tell me if this is the loop's
first iteration

do {
if( (File.peek() == 32) && r)
return 0;
else if ... snip
else ... snip
r=0;
} while(some condition)

I've done this because I want to know if my function encounters the
newline
character before everything else. If it does, I need it to return false.
If it doesn't, I need it to make r=0, so that on the next iteration if it
happens to find a newline char, but it's not the first iteration, it won't
return false.

What about:

if ( File.peek() == 32 ) {
return ( 0 );
}
do {
if ... snip
else ... snip
} while ( some condition );

What I don't like is that let's say 100 iterations of this loop happens
before it returns anything. I'm wasting processor time by assigning 0 to
r every single iteration.

Google "premature optimization".

Therefore my question is: is there not a way for me to change that if ( )
statement up there so that I can somehow see if this is the first
iteration of the do...while() loop, WITHOUT having to use a variable and
waste processor time assigning it all the time?

No. There is no built-in way to check whether you are in the first iteration
of a loop.
Best

Kai-Uwe Bux

[Jim Langston]

drmario wrote:

Here's what I got:

ifstream File; // already initialized and associated with a
file input stream
unsigned short r = 1; // a counter to tell me if this is the
loop's first iteration

do {
if( (File.peek() == 32) && r)
return 0;
else if ... snip
else ... snip
r=0;
} while(some condition)

if ( File.peek() == 32 )
return 0;

do {
/* your loop here */
}

I've done this because I want to know if my function encounters the
newline character before everything else. If it does, I need it to
return false. If it doesn't, I need it to make r=0, so that on the
next iteration if it happens to find a newline char, but it's not the
first iteration, it won't return false.

What I don't like is that let's say 100 iterations of this loop
happens before it returns anything. I'm wasting processor time by
assigning 0 to r every single iteration.

Therefore my question is: is there not a way for me to change that if
( ) statement up there so that I can somehow see if this is the first
iteration of the do...while() loop, WITHOUT having to use a variable
and waste processor time assigning it all the time?

thanks
Mario

--
Jim Langston
ta*******@rocketmail.com

[Juha Nieminen]

drmario wrote:

I'm wasting processor time by assigning 0 to r
every single iteration.

Your File.peek() probably takes hundreds of clock cycles. That
assignment doesn't have any significant slowing effect compared. Trying
to remove it would be completely useless "optimization".

[drmario]

"Kai-Uwe Bux" <jk********@gmx.netwrote in message
news:fv**********@aioe.org...

What about:

if ( File.peek() == 32 ) {
return ( 0 );
}
do {
if ... snip
else ... snip
} while ( some condition );

It would seem that all you've done there is remove the "&& r" part of the if
condition. That will not work for me because checking whether or not r is 1
(I think I forgot to mention, I initialize r to 1 when its declared) is part
of the decision whether or not to return 0.

>What I don't like is that let's say 100 iterations of this loop happens
before it returns anything. I'm wasting processor time by assigning 0 to
r every single iteration.

Google "premature optimization".

Will do.

>Therefore my question is: is there not a way for me to change that if ( )
statement up there so that I can somehow see if this is the first
iteration of the do...while() loop, WITHOUT having to use a variable and
waste processor time assigning it all the time?

No. There is no built-in way to check whether you are in the first
iteration
of a loop.

That sucks.

Thanks for the help.

[drmario]

"Juha Nieminen" <no****@thanks.invalidwrote in message
news:bo************@read4.inet.fi...

drmario wrote:

>I'm wasting processor time by assigning 0 to r
every single iteration.

Your File.peek() probably takes hundreds of clock cycles. That
assignment doesn't have any significant slowing effect compared. Trying
to remove it would be completely useless "optimization".

So in other words, *in this particular case* don't worry about it since
removing 100 repetitions of r=0 would make only an infintesmal difference?

[Kai-Uwe Bux]

drmario wrote:

"Kai-Uwe Bux" <jk********@gmx.netwrote in message
news:fv**********@aioe.org...

>What about:

if ( File.peek() == 32 ) {
return ( 0 );
}
do {
if ... snip
else ... snip
} while ( some condition );

It would seem that all you've done there is remove the "&& r" part of the
if condition.

[snip]

Have a closer look: I also moved the check in front of the loop. Therefore,
the return(0) clause will only hit in what was the 1st iteration of your
code. In fact, the version I gave is completely equivalent to yours (and a
good optimizing compiler might even create identical object code from it).

For context and comparison, here is your code:

unsigned short r = 1;
do {
if( (File.peek() == 32) && r)
return 0;
else if ... snip
else ... snip
r=0;
} while(some condition)

Best

Kai-Uwe Bux