std vector, QVector and fields..
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@J-Hilk
OK, yes, I know about turning the C++ compiler into an interpreter withconstexpr:) But thatfibonaccifunction is self-contained. Compiler is not going to be able to execute anything likeconstexpr QObject::findChildren<QCheckBox *>, it's runtime-only.Purely BTW. I'm not a great programmer (nor mathematician), so while I develop my code I have a go at:
constexpr int64_t fibonacci(const int64_t n) { int64_t result = 0; while (n > 0) result += n; return result; }Now I compile my code. Does the compilation simply hang??
@JonB said in std vector, QVector and fields..:
Now I compile my code. Does the compilation simply hang??
No, because you're not calling it :-)
And it would not hang if you would call it with any number as parameter. It could probably slow down compilation if you would pass a huge number :-) -
@JonB said in std vector, QVector and fields..:
Now I compile my code. Does the compilation simply hang??
No, because you're not calling it :-)
And it would not hang if you would call it with any number as parameter. It could probably slow down compilation if you would pass a huge number :-)wrote on 29 Oct 2020, 07:43 last edited by JonB@jsulm
Oh yes I am! In @J-Hilk's code (at least originally) hismain()callsfibonacci(10), so assume that, and then tell me what happens while I sit waiting for the compilation to finish?And it would not hang if you would call it with any number as parameter. It could probably slow down compilation if you would pass a huge number :-)
I think you should look at the code again... :)
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@jsulm
Oh yes I am! In @J-Hilk's code (at least originally) hismain()callsfibonacci(10), so assume that, and then tell me what happens while I sit waiting for the compilation to finish?And it would not hang if you would call it with any number as parameter. It could probably slow down compilation if you would pass a huge number :-)
I think you should look at the code again... :)
@JonB OK, I see n > 0. You should try :-)
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@jsulm
Oh yes I am! In @J-Hilk's code (at least originally) hismain()callsfibonacci(10), so assume that, and then tell me what happens while I sit waiting for the compilation to finish?And it would not hang if you would call it with any number as parameter. It could probably slow down compilation if you would pass a huge number :-)
I think you should look at the code again... :)
@JonB Add at least a function call to your calculation, then you get an stack overflow(eventually)
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You should try :-)
I'm terrified of seizing up my Linux VM :) It already does that if I accidentally debug from Creator when inside a
QComboBoxclicked slot, and I have to hard-switch-off the whole VM... :(main.cpp:158:18: error: expression is not an integral constant expression main.cpp:152:13: note: constexpr evaluation hit maximum step limit; possible infinite loop? main.cpp:158:18: note: in call to 'fibonacci(25)'smart things these compilers
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@JonB Add at least a function call to your calculation, then you get an stack overflow(eventually)
wrote on 29 Oct 2020, 07:49 last edited by@J-Hilk said in std vector, QVector and fields..:
@JonB Add at least a function call to your calculation, then you get an stack overflow(eventually)
But I don't want a stackoverflow to terminate! I want to know whether the compiler sits there forever! Which is why I wrote as I did.
OK, I'm off to try....
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main.cpp:158:18: error: expression is not an integral constant expression main.cpp:152:13: note: constexpr evaluation hit maximum step limit; possible infinite loop? main.cpp:158:18: note: in call to 'fibonacci(25)'smart things these compilers
wrote on 29 Oct 2020, 07:50 last edited by@J-Hilk said in std vector, QVector and fields..:
note: constexpr evaluation hit maximum step limit; possible infinite loop?
Ah ha! So..... this C++
constexprhas what "maximum step limit`? Where is that in the spec? :) -
@J-Hilk said in std vector, QVector and fields..:
note: constexpr evaluation hit maximum step limit; possible infinite loop?
Ah ha! So..... this C++
constexprhas what "maximum step limit`? Where is that in the spec? :)@JonB up to you with the compiler option
-fconstexpr-steps -
wrote on 29 Oct 2020, 07:56 last edited by
@J-Hilk
Wow! They think of everything! I wonder if that would accept-fconstexpr-steps fibonacci(25);-)OK, enough now, thanks!
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