while and for question

i was wondering whish is faster for(;;) or while(true) as for myself i think for(;;) is faster coz it doesnt chk if value is 1 is just keep going on and on

But I don't have a ;) key...

I think most compilers will optimize that code down to the same assembler instructions anyway, so it doesn't matter.

QuantumPete

Quote:

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Originally Posted by QuantumPete

I think most compilers will optimize that code down to the same assembler instructions anyway, so it doesn't matter.

QuantumPete

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while(true)

can cause a warning "conditional expression is constant"

while

Code:

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for(;;)

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does not such thing

Quote:

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Originally Posted by vart

while(true)

can cause a warning "conditional expression is constant"

while

Code:

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for(;;)

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does not such thing

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Hmm, I wonder why that is. Surely both do the exact same thing?

QuantumPete

I remember reading in an old book about optimisation in C that noted that compilers regarded old at the time of writing would produce code that evaluated the constant expression in:

Code:

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while (true)

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or more accurately, since true is a C++ keyword and C99 macro:

Code:

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while (1)

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but those same compilers would correctly produce "infinite loop" code when they encountered:

Code:

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for (;;)

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No doubt this is not true of modern compilers, but it is of historical interest, and thus I decided to prefer the latter because it is arguably more "canonical" :)

Quote:

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Hmm, I wonder why that is.

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because

Code:

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while(1)

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could be a mistake and written instead of

Code:

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while(l)

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for example

On the same reason

Code:

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if(f=fopen...)

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could produce a warning about assignment in the if instead of comparison

Quote:

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Originally Posted by vart

because

Code:

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while(1)

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could be a mistake and written instead of

Code:

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while(l)

---

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So do you think it is a good idea to subject people to warnings for mistakes they did not make?

Snafuist posted this rather amusing set of related facts the other day.

Quote:

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Originally Posted by MK27

So do you think it is a good idea to subject people to warnings for mistakes they did not make?

Snafuist posted this rather amusing set of related facts the other day.

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I prefer to have a warning about the correct code (I always have a way to silence it here) then not to have a warning about the incorrect code

I always get plenty of

warning C4706: assignment within conditional expression

when I do something like

Code:

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if (!(lf = fopen(LOGFILE_NAME, "a"))) {
    printf("Failure to create or open logfile: %s\n", LOGFILE_NAME);
    ...
    }


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When it's exactly what I want to say. But then I always use warning levels = 4 (highest).

Quote:

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Originally Posted by nonoob

I always get plenty of

warning C4706: assignment within conditional expression

when I do something like

Code:

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if (!(lf = fopen(LOGFILE_NAME, "a"))) {
    printf("Failure to create or open logfile: %s\n", LOGFILE_NAME);
    ...
    }


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When it's exactly what I want to say. But then I always use warning levels = 4 (highest).

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Change it to this and the warning should go away:

Code:

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if ( (lf = fopen(LOGFILE_NAME, "a")) == 0 )

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