What's the difference between "STL" and "C++ Standard Library"?

Question

Someone brought this article to my attention that claims (I'm paraphrasing) the STL term is misused to refer to the entire C++ Standard Library instead of the parts that were taken from SGI STL.

(...) it refers to the "STL", despite the fact that very few people still use the STL (which was designed at SGI).

Parts of the C++ Standard Library were based on parts of the STL, and it is these parts that many people (including several authors and the notoriously error-ridden cplusplus.com) still refer to as "the STL". However, this is inaccurate; indeed, the C++ standard never mentions "STL", and there are content differences between the two.

(...) "STL" is rarely used to refer to the bits of the stdlib that happen to be based on the SGI STL. People think it's the entire standard library. It gets put on CVs. And it is misleading.

I hardly know anything about C++'s history so I can't judge the article's correctness. Should I refrain from using the term STL? Or is this an isolated opinion?

Answer 1

The "STL" was written by Alexander Stepanov in the days long before C++ was standardised. C++ existed through the 80s, but what we now call "C++" is the language standardised in ISO/IEC 14882:2014 (and earlier versions, such as ISO/IEC 14882:2011).

The STL was already widely used as a library for C++, giving programmers access to containers, iterators and algorithms. When the standardisation happened, the language committee designed parts of the C++ Standard Library (which is part of the language standard) to very closely match the STL.

Over the years, many people — including prominent book authors, and various websites — have continued to refer to the C++ Standard Library as "the STL", despite the fact that the two entities are separate and that there are some differences. These differences are even more pronounced in the upcoming new C++ standard, which includes various features and significantly alters some classes.

The original STL is now often called "an implementation of the C++ Standard Template Library" (rather backwards to actual history!), in the same way that your Microsoft Visual Studio or GCC ships an implementation of the C++ Standard Library. But the "Standard Template Library" and the "Standard Library" are not the same thing.

The battle is about whether the current Standard Library should be called "the STL" in whole or in part, and/or whether it matters what it's called.

For "STL"

There is a school of thought that says that everybody knows now that "STL" means the standard library, just as everybody now knows that "C++" is the ISO-standardised language.

It also includes those who believe that it doesn't really matter as long as all parties understand what is being talked about.

It's a term made even more prevalent by the nature of the beast, much of which makes heavy use of the C++ feature known as "templates".

For "C++ Standard Library" (or stdlib)

However, there is another school of thought — to which I subscribe — that says that this is confusing. People learning C++ for the first time do not know this distinction, and may not notice small language differences.

The author of that article has numerous times encountered people who believe that the entire C++ Standard Library is the STL, including features that were never part of the STL itself. Most vocal proponents of "the STL", in contrast, know exactly what they mean by it and refuse to believe that not everybody "gets it". Clearly, the term's usage is not uniform.

In addition, there are some STL-like libraries that are in fact implementations of the original STL, not the C++ Standard Library. Until recently, STLPort was one of them (and even there, the confusion abounds!).

Further, the C++ Standard does not contain the text "STL" anywhere, and some people habitually employ phrases like "the STL is included in the C++ Standard Library", which is plain incorrect.

It's my belief that continuing to propagate the usage of the term in this way will just lead to the misunderstanding going on forever. Alas, it may be entirely counter-productive to attempt to change things, even if it's supposed to be for the better. We may just be stuck with double-meanings forever.

Conclusion

I appreciate that this post has been a little biased: I wrote the article you linked to. :) Anyway, I hope this helps to explain the battle a bit better.

Update 13/04/2011

Here are three perfect examples of someone who is using "the STL" to refer to the entire C++ Standard Library. It continues to baffle me that so many people swear blind that nobody ever does this, when it's plain to see almost on a daily basis.

Answer 2

There is no one answer that's really correct. Alexander Stepanov developed a library he called STL (working for HP at the time). That library was then proposed for inclusion in the C++ standard.

That basically "forked" development. The committee included some parts, rejected others completely, and redesigned a few (with Alexander's participation). Development of the original library was later moved to Silicon Graphics, but continued separately from the C++ standard library.

After those pieces were added to the standard library, some other parts of the standard library were modified to fit better with what was added (e.g., begin, end, rbegin and rend were added to std::string so it could be used like a container). Around the same time, most of the library (even pieces that were completely unrelated) were made into templates to accommodate different types (e.g., standard streams).

Some people also use STL as just a short form of "STandard Library".

That means when somebody uses the term "STL" they could be referring to any of about half a dozen different things. For better or worse, most people who use it seem to ignore the multiplicity of meanings, and assume that everybody else will recognize what they're referring to. This leads to many misunderstandings, and at least a few serious flame-wars that made most of the participants look foolish because they were simply talking about entirely different things.

Unfortunately, the confusion is likely to continue unabated. It's much more convenient to refer to "STL" than something like "the containers, iterators, and algorithms in the C++ standard library, but not including std::string, even though it can act like a container." Even though "C++ standard library" isn't quite as long and clumsy as that, "STL" is still a lot shorter and simpler still. Until or unless somebody invents terms that are more precise (when necessary), and just as convenient, "STL" will continue to be used and confusion will continue to result.