When should the STL algorithms be used instead of

Question

I frequently use the STL containers but have never used the STL algorithms that are to be used with the STL containers.

One benefit of using the STL algorithms is that they provide a method for removing loops so that code logic complexity is reduced. There are other benefits that I won't list here.

I have never seen C++ code that uses the STL algorithms. From sample code within web page articles to open source projects, I haven't seen their use.

Are they used more frequently than it seems?

Answer 1

STL algorithms should be used whenever they fit what you need to do. Which is almost all the time.

Answer 2

When you think you can code it better than a really clever coder who spents weeks researching and testing and trying to cope with every conceivable set of inputs.

For most Earthlings the answer is NEVER!

Answer 3

If I had to write something due this afternoon, and I knew how to do it using hand-made loops and would need to figure out how to do it in STL algorithms, I would write it using hand-made loops.

Having said that, I would work to make the STL algorithms a reliable part of my toolkit, for reasons articulated in the other answers.

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Reasons you might not see it is in code is that it is either legacy code or written by legacy programmers. We had about 20 years of C++ programming before the STL came out, and at that point we had a community of programmers who knew how to do things the old way and had not yet learned the STL way. This will likely remain for a generation.

Answer 4

Short answer: Always.

Long answer: Always. That's what they are there for. They're optimized for use with STL containers, and they're faster, clearer, and more idiomatic than anything you can write yourself. The only situation you should consider rolling your own is if you can articulate a very specific, mission-critical need that the STL algorithms don't satisfy.

Edited to add: (Okay, so not really really always, but if you have to ask whether you should use STL, the answer is "yes".)

Answer 5

When should the STL algorithms be used instead of using your own?

When you value your time and sanity and have more fun things to do than reinventing the wheel again and again.

You need to use your own algorithms when project demands it, and there are no acceptable alternatives to writing stuff yourself, or if you identified STL algorithm as a bottleneck (using profiler, of course), or have some kind of restrictions STL doesn't conform to, or adapting STL for the task will take longer than writing algorithm from scratch (I had to use twisted version of binary search few times...). STL is not perfect and isn't fit for everything, but when you can, you should use it. When someone already did all the work for you, there is frequently no reason to do the same thing again.

Answer 6

Bear in mind that the STL algorithms cover a lot of bases, but most C++ developers will probably end up coding something that does something equivalent to std::find(), std::find_if() and std::max() almost every day of their working lives (if they're not using the STL versions already). By using the STL versions you separate the algorithm from both the logical flow of your code and from the data representation.

For other less commonly used STL algorithms such as std::merge() or std::lower_bound() these are hugely useful routines (the first for merging two sorted containers, the second for working out where to insert an item in a container to keep it ordered). If you were to try to implement them yourself then it would probably take a few attempts (the algorithms aren't complicated, but you'd probably get off-by-one errors or the like).

I myself use them every day of my professional career. Some legacy codebases that predate a stable STL may not use it as extensively, but if there's a newer project that is intentionally avoiding it I would be inclined to think it was by a part-time hacker who was still labouring under the mid-90's assumption that templates are slow and therefore to be avoided.