Thread: while and for question

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

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

while(true)

can cause a warning "conditional expression is constant"

while

Code:

for(;;)

does not such thing

Originally Posted by vart

while(true)

can cause a warning "conditional expression is constant"

while

Code:

for(;;)

does not such thing

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:

while (true)

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

Code:

while (1)

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

Code:

for (;;)

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"

Hmm, I wonder why that is.

because

Code:

while(1)

could be a mistake and written instead of

Code:

while(l)

for example

On the same reason

Code:

if(f=fopen...)

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

Originally Posted by vart

because

Code:

while(1)

could be a mistake and written instead of

Code:

while(l)

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.

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.

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:

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

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

Originally Posted by nonoob

I always get plenty of

warning C4706: assignment within conditional expression

when I do something like

Code:

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

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

Change it to this and the warning should go away:

Code:

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