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Re: calling exit in response to an error shouldn't be an error...

I am not a GCC developer, just a regular user of C. But I have some comments below:

On 6/9/2019 3:21 PM, L A Walsh wrote:
If I have a function returning NULL on error (including EOF).

So the program calls exit if the function doesn't return
a non-zero value (func() || exit(1)).

I have:


main() { char * buf[512];
     while (gets(buf) || exit(0)) puts(buf);

-- compile w/:
gcc -fpermissive --no-warnings  -o /tmp/ex /tmp/ex.c

/tmp/ex.c: In function ‘main’:
/tmp/ex.c:2:22: error: void value not ignored as it ought to be
   while (gets(buf) || exit(0) ) puts(buf);

I understand that the while is testing the value of exit
"when it returns", but since it doesn't, why flag an error
(if exit is part of C-standard?) but *especially*, why
not a warning, like a type mismatch or such?i

There is a slight misunderstanding of operators here. This is not while testing the value of exit(0). This is the "||" operator. It needs a value on *both* sides of || so it can evaluate them both and return a boolean result. Your code has no value on the right-hand side so it's meaningless.

But this:


main(){ char * buf[512];
   while (1) {
     fgets(buf) || exit(1);

---compile + output:
gcc -fpermissive --no-warnings  -o /tmp/ex2 /tmp/ex2.c
/tmp/ex2.c: In function ‘main’:
/tmp/ex2.c:4:18: error: void value not ignored as it ought to be
     fgets(buf) || exit(1);

Ultra confusing -- how is exit value used?  Isn't it thrown away?

Same problem here.

I haven't tested it but you might be able to make this work with a comma operator like "while (gets(buf) || (exit(0), 1)) puts(buf);"

Oh, and "gets" is no longer a function. It's not just deprecated. It's *gone*.

                Knowledge is Power -- Power Corrupts
                        Study Hard -- Be Evil

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