27

Given a container of boolean values (An example is std::vector<bool>), is there a standard function that returns true if all the values are true ("and") or true if at least one value is true ("or"), with short circuit evalutation ?

I digged trough www.cplusplus.com this morning but couldn't find anything close.

Dancrumb
  • 26,597
  • 10
  • 74
  • 130
ereOn
  • 53,676
  • 39
  • 161
  • 238
  • You can easily implement your own... – Daniel Jun 28 '11 at 12:50
  • 9
    @Dani: Indeed. But even if the code is trivial, if there is anything that already exists, why would I rewrite it ? – ereOn Jun 28 '11 at 12:52
  • @ereOn, things that are easily implemented don't go into c++. if you want that try c# or even some interpreter. – Daniel Jun 28 '11 at 12:53
  • 5
    @Dani Nonsense. See `` and `` for tons of convenience functions and classes whose implementation is trivial. – Konrad Rudolph Jun 28 '11 at 13:02
  • 2
    @Dani: There is no pride to get from writing something trivial. No offense, but your comment reminds me of a guy at my work that refuses to use shared pointers and `std::string` because he **knows** how to do that himself. Sure he does, but as a result his code is often unmaintainable and cluttered with trivial tricks. – ereOn Jun 28 '11 at 13:05
  • 1
    Did you look at the size of std::string? its huge, not trivial. however, 3 line `for`, is. – Daniel Jun 28 '11 at 13:35
  • 1
    cplusplus.com is a poor resource. – Lightness Races in Orbit Jun 28 '11 at 13:36
  • 1
    @Dani: `std::string` is "huge"? – Lightness Races in Orbit Jun 28 '11 at 13:36
  • string after concating its different files is 15312 lines – Daniel Jun 28 '11 at 13:40
  • @Dani: Repeat those 3 lines one hundred times and compare it to what you would have got using one of the "one-liners" below: you just lost 200 hundred lines of trivial code that brings **nothing**. – ereOn Jun 28 '11 at 14:17
  • @ereOn, you can say it for pretty much everything... and if you excessively use this in your application just make an inlined function/macro for it – Daniel Jun 28 '11 at 14:19
  • 4
    @Dani: So I would end up with a one-line, inlinable function maintained by me in place of a... one-line, inlinable function maintained by the people who built my compiler. What is the next step ? Rewriting my own `memcpy` or `std::copy` ? After all, it is just a single `for` loop. – ereOn Jun 28 '11 at 14:24
  • I don't know about `std::copy`, but `memcpy` uses some processor specific instructions which make it faster... and what I meant is that the c++ library will just become more bloated when people like you ask for features that you can use for yourself. a simple static hello world is already few kilobytes when all it does is write 1 line to the screen. – Daniel Jun 28 '11 at 14:29
  • 4
    @Dani: The good thing is that there must be a lot of people "like me" since C++0x includes `std::all_of` and `std::any_of` :) Moreover, if these simple functions are inlinable (which they surely are), what size difference with "rolling out my own version of these functions" does it make anyway ? – ereOn Jun 28 '11 at 14:36

4 Answers4

52

is there a standard function that returns true if all the values are true ("and")

std::all_of(vec.begin(), vec.end(), [](bool x) { return x; } )

or true if at least one value is true ("or")

std::any_of(vec.begin(), vec.end(), [](bool x) { return x; } )

with short circuit evalutation?

I just inserted print statements into the lambda, and yes, both functions perform short-circuiting.

fredoverflow
  • 256,549
  • 94
  • 388
  • 662
42

You can implement by:

AND:

std::find(vector.begin(), vector.end(), false) == vector.end() // all the values are true

OR:

std::find(vector.begin(), vector.end(), true) != vector.end() //at least one value is true
Igor
  • 26,650
  • 27
  • 89
  • 114
  • 1
    Well sometimes I guess I'm searching too hard... And I can even use `find_if` with a function object if I need to perform a more complicated check on the values. Thank you very much ! – ereOn Jun 28 '11 at 12:57
  • I accepted FredOverflow's answer because his solution is more straightforward. Upvoted this one for fairness and because it is really clever. – ereOn Jun 28 '11 at 13:16
  • 1
    @ereOn: But you said that you can't use Fred's answer as your solution. – Lightness Races in Orbit Jun 28 '11 at 13:37
  • @Tomalak: Indeed. I can't use it right now, but it still seems to be the recommended way to do this. I actually implemented the two solutions and commented out one of them until I can use it. – ereOn Jun 28 '11 at 14:07
  • 2
    @ereOn: Recommended if you have C++0x. I won't use non-standard features in critical production code, though. If you want a standard C++ solution -- and, incidentally, one that actually works for you ereOn -- then this is the correct answer, at present, to the stated problem. That a future standard makes it a bit easier is an interesting sidenote. – Lightness Races in Orbit Jun 28 '11 at 14:24
12

You can use the function objects logical_and and logical_or in conjunction with a reduction to accomplish that.

accumulate calculates the reduction. Hence:

bool any = std::accumulate(foo.begin(), foo.end(), false, std::logical_or<>());
bool all = std::accumulate(foo.begin(), foo.end(), true, std::logical_and<>());

Caveat: this is not using short-circuiting (the accumulate function knows nothing about short-circuiting even though the functors do), while Igor’s clever solution is.

Konrad Rudolph
  • 530,221
  • 131
  • 937
  • 1,214
1

If you do not need a generic algorithm for different container types...

As you are looking for short circuit evaluation, you may give std::valarray a chance. For and use valarray::min() == true for or you could use std::find as mentioned by Igor.

In case you know the number of elements to store at compile time, you could even use a std::bitset:

bitset<100> container();

//... fill bitset

bool or = container.any();
bool and = container.count() == container.size();
Stephan
  • 4,187
  • 1
  • 21
  • 33