Effective STL: 50 Specific Ways to Improve Your Use of the Standard Template Library

Author: Scott Meyers
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Effective STL: 50 Specific Ways to Improve Your Use of the Standard Template Library

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by anonymous   2017-08-20

TL;DR

Extra parentheses change the meaning of a C++ program in the following contexts:

  • preventing argument-dependent name lookup
  • enabling the comma operator in list contexts
  • ambiguity resolution of vexing parses
  • deducing referenceness in decltype expressions
  • preventing preprocessor macro errors

Preventing argument-dependent name lookup

As is detailed in Annex A of the Standard, a post-fix expression of the form (expression) is a primary expression, but not an id-expression, and therefore not an unqualified-id. This means that argument-dependent name lookup is prevented in function calls of the form (fun)(arg) compared to the conventional form fun(arg).

3.4.2 Argument-dependent name lookup [basic.lookup.argdep]

1 When the postfix-expression in a function call (5.2.2) is an unqualified-id, other namespaces not considered during the usual unqualified lookup (3.4.1) may be searched, and in those namespaces, namespace-scope friend function or function template declarations (11.3) not otherwise visible may be found. These modifications to the search depend on the types of the arguments (and for template template arguments, the namespace of the template argument). [ Example:

namespace N {
    struct S { };
    void f(S);
}

void g() {
    N::S s;
    f(s);   // OK: calls N::f
    (f)(s); // error: N::f not considered; parentheses
            // prevent argument-dependent lookup
}

—end example ]

Enabling the comma operator in list contexts

The comma operator has a special meaning in most list-like contexts (function and template arguments, initializer lists etc.). Parentheses of the form a, (b, c), d in such contexts can enable the comma operator compared to the regular form a, b, c, d where the comma operator does not apply.

5.18 Comma operator [expr.comma]

2 In contexts where comma is given a special meaning, [ Example: in lists of arguments to functions (5.2.2) and lists of initializers (8.5) —end example ] the comma operator as described in Clause 5 can appear only in parentheses. [ Example:

f(a, (t=3, t+2), c);

has three arguments, the second of which has the value 5. —end example ]

Ambiguity resolution of vexing parses

Backward compatibility with C and its arcane function declaration syntax can lead to surprising parsing ambiguities, known as vexing parses. Essentially, anything that can be parsed as a declaration will be parsed as one, even though a competing parse would also apply.

6.8 Ambiguity resolution [stmt.ambig]

1 There is an ambiguity in the grammar involving expression-statements and declarations: An expression-statement with a function-style explicit type conversion (5.2.3) as its leftmost subexpression can be indistinguishable from a declaration where the first declarator starts with a (. In those cases the statement is a declaration.

8.2 Ambiguity resolution [dcl.ambig.res]

1 The ambiguity arising from the similarity between a function-style cast and a declaration mentioned in 6.8 can also occur in the context of a declaration. In that context, the choice is between a function declaration with a redundant set of parentheses around a parameter name and an object declaration with a function-style cast as the initializer. Just as for the ambiguities mentioned in 6.8, the resolution is to consider any construct that could possibly be a declaration a declaration. [ Note: A declaration can be explicitly disambiguated by a nonfunction-style cast, by an = to indicate initialization or by removing the redundant parentheses around the parameter name. —end note ] [ Example:

struct S {
    S(int);
};

void foo(double a) {
    S w(int(a));  // function declaration
    S x(int());   // function declaration
    S y((int)a);  // object declaration
    S z = int(a); // object declaration
}

—end example ]

A famous example of this is the Most Vexing Parse, a name popularized by Scott Meyers in Item 6 of his Effective STL book:

ifstream dataFile("ints.dat");
list<int> data(istream_iterator<int>(dataFile), // warning! this doesn't do
               istream_iterator<int>());        // what you think it does

This declares a function, data, whose return type is list<int>. The function data takes two parameters:

  • The first parameter is named dataFile. It's type is istream_iterator<int>. The parentheses around dataFile are superfluous and are ignored.
  • The second parameter has no name. Its type is pointer to function taking nothing and returning an istream_iterator<int>.

Placing extra parentheses around the first function argument (parentheses around the second argument are illegal) will resolve the ambiguity

list<int> data((istream_iterator<int>(dataFile)), // note new parens
                istream_iterator<int>());          // around first argument
                                                  // to list's constructor

C++11 has brace-initializer syntax that allows to side-step such parsing problems in many contexts.

Deducing referenceness in decltype expressions

In contrast to auto type deduction, decltype allows referenceness (lvalue and rvalue references) to be deduced. The rules distinguish between decltype(e) and decltype((e)) expressions:

7.1.6.2 Simple type specifiers [dcl.type.simple]

4 For an expression e, the type denoted by decltype(e) is defined as follows:

— if e is an unparenthesized id-expression or an unparenthesized class member access (5.2.5), decltype(e) is the type of the entity named by e. If there is no such entity, or if e names a set of overloaded functions, the program is ill-formed;

— otherwise, if e is an xvalue, decltype(e) is T&&, where T is the type of e;

— otherwise, if e is an lvalue, decltype(e) is T&, where T is the type of e;

— otherwise, decltype(e) is the type of e.

The operand of the decltype specifier is an unevaluated operand (Clause 5). [ Example:

const int&& foo();
int i;
struct A { double x; };
const A* a = new A();
decltype(foo()) x1 = 0;   // type is const int&&
decltype(i) x2;           // type is int
decltype(a->x) x3;        // type is double
decltype((a->x)) x4 = x3; // type is const double&

—end example ] [ Note: The rules for determining types involving decltype(auto) are specified in 7.1.6.4. —end note ]

The rules for decltype(auto) have a similar meaning for extra parentheses in the RHS of the initializing expression. Here's an example from the C++FAQ and this related Q&A

decltype(auto) look_up_a_string_1() { auto str = lookup1(); return str; }  //A
decltype(auto) look_up_a_string_2() { auto str = lookup1(); return(str); } //B

The first returns string, the second returns string &, which is a reference to the local variable str.

Preventing preprocessor macro related errors

There is a host of subtleties with preprocessor macros in their interaction with the C++ language proper, the most common of which are listed below

  • using parentheses around macro parameters inside the macro definition #define TIMES(A, B) (A) * (B); in order to avoid unwanted operator precedence (e.g. in TIMES(1 + 2, 2 + 1) which yields 9 but would yield 6 without the parentheses around (A) and (B)
  • using parentheses around macro arguments having commas inside: assert((std::is_same<int, int>::value)); which would otherwise not compile
  • using parentheses around a function to protect against macro expansion in included headers: (min)(a, b) (with the unwanted side effect of also disabling ADL)
by Klaim   2017-08-20

I think you'd better have some lectures about good practices and why they are good. That should help you more than a code analysis tool (in the beginning at least).

I suggest you read the series of Effective C++ and **Effective STL books, at least. See alsot The Definitive C++ Book Guide and List

by litb   2017-08-20

Beginner

Introductory, no previous programming experience

  • Programming: Principles and Practice Using C++ (Bjarne Stroustrup) (updated for C++11/C++14) An introduction to programming using C++ by the creator of the language. A good read, that assumes no previous programming experience, but is not only for beginners.

Introductory, with previous programming experience

  • C++ Primer * (Stanley Lippman, Josée Lajoie, and Barbara E. Moo) (updated for C++11) Coming at 1k pages, this is a very thorough introduction into C++ that covers just about everything in the language in a very accessible format and in great detail. The fifth edition (released August 16, 2012) covers C++11. [Review]

  • A Tour of C++ (Bjarne Stroustrup) (EBOOK) The “tour” is a quick (about 180 pages and 14 chapters) tutorial overview of all of standard C++ (language and standard library, and using C++11) at a moderately high level for people who already know C++ or at least are experienced programmers. This book is an extended version of the material that constitutes Chapters 2-5 of The C++ Programming Language, 4th edition.

  • Accelerated C++ (Andrew Koenig and Barbara Moo) This basically covers the same ground as the C++ Primer, but does so on a fourth of its space. This is largely because it does not attempt to be an introduction to programming, but an introduction to C++ for people who've previously programmed in some other language. It has a steeper learning curve, but, for those who can cope with this, it is a very compact introduction into the language. (Historically, it broke new ground by being the first beginner's book to use a modern approach at teaching the language.) [Review]

  • Thinking in C++ (Bruce Eckel) Two volumes; is a tutorial style free set of intro level books. Downloads: vol 1, vol 2. Unfortunately they’re marred by a number of trivial errors (e.g. maintaining that temporaries are automatically const), with no official errata list. A partial 3rd party errata list is available at (http://www.computersciencelab.com/Eckel.htm), but it’s apparently not maintained.

* Not to be confused with C++ Primer Plus (Stephen Prata), with a significantly less favorable review.

Best practices

  • Effective C++ (Scott Meyers) This was written with the aim of being the best second book C++ programmers should read, and it succeeded. Earlier editions were aimed at programmers coming from C, the third edition changes this and targets programmers coming from languages like Java. It presents ~50 easy-to-remember rules of thumb along with their rationale in a very accessible (and enjoyable) style. For C++11 and C++14 the examples and a few issues are outdated and Effective Modern C++ should be preferred. [Review]

  • Effective Modern C++ (Scott Meyers) This is basically the new version of Effective C++, aimed at C++ programmers making the transition from C++03 to C++11 and C++14.

  • Effective STL (Scott Meyers) This aims to do the same to the part of the standard library coming from the STL what Effective C++ did to the language as a whole: It presents rules of thumb along with their rationale. [Review]

Intermediate

  • More Effective C++ (Scott Meyers) Even more rules of thumb than Effective C++. Not as important as the ones in the first book, but still good to know.

  • Exceptional C++ (Herb Sutter) Presented as a set of puzzles, this has one of the best and thorough discussions of the proper resource management and exception safety in C++ through Resource Acquisition is Initialization (RAII) in addition to in-depth coverage of a variety of other topics including the pimpl idiom, name lookup, good class design, and the C++ memory model. [Review]

  • More Exceptional C++ (Herb Sutter) Covers additional exception safety topics not covered in Exceptional C++, in addition to discussion of effective object oriented programming in C++ and correct use of the STL. [Review]

  • Exceptional C++ Style (Herb Sutter) Discusses generic programming, optimization, and resource management; this book also has an excellent exposition of how to write modular code in C++ by using nonmember functions and the single responsibility principle. [Review]

  • C++ Coding Standards (Herb Sutter and Andrei Alexandrescu) “Coding standards” here doesn't mean “how many spaces should I indent my code?” This book contains 101 best practices, idioms, and common pitfalls that can help you to write correct, understandable, and efficient C++ code. [Review]

  • C++ Templates: The Complete Guide (David Vandevoorde and Nicolai M. Josuttis) This is the book about templates as they existed before C++11. It covers everything from the very basics to some of the most advanced template metaprogramming and explains every detail of how templates work (both conceptually and at how they are implemented) and discusses many common pitfalls. Has excellent summaries of the One Definition Rule (ODR) and overload resolution in the appendices. A second edition is scheduled for 2017. [Review]


Advanced

  • Modern C++ Design (Andrei Alexandrescu) A groundbreaking book on advanced generic programming techniques. Introduces policy-based design, type lists, and fundamental generic programming idioms then explains how many useful design patterns (including small object allocators, functors, factories, visitors, and multimethods) can be implemented efficiently, modularly, and cleanly using generic programming. [Review]

  • C++ Template Metaprogramming (David Abrahams and Aleksey Gurtovoy)

  • C++ Concurrency In Action (Anthony Williams) A book covering C++11 concurrency support including the thread library, the atomics library, the C++ memory model, locks and mutexes, as well as issues of designing and debugging multithreaded applications.

  • Advanced C++ Metaprogramming (Davide Di Gennaro) A pre-C++11 manual of TMP techniques, focused more on practice than theory. There are a ton of snippets in this book, some of which are made obsolete by typetraits, but the techniques, are nonetheless useful to know. If you can put up with the quirky formatting/editing, it is easier to read than Alexandrescu, and arguably, more rewarding. For more experienced developers, there is a good chance that you may pick up something about a dark corner of C++ (a quirk) that usually only comes about through extensive experience.


Reference Style - All Levels

  • The C++ Programming Language (Bjarne Stroustrup) (updated for C++11) The classic introduction to C++ by its creator. Written to parallel the classic K&R, this indeed reads very much alike it and covers just about everything from the core language to the standard library, to programming paradigms to the language's philosophy. [Review]

  • C++ Standard Library Tutorial and Reference (Nicolai Josuttis) (updated for C++11) The introduction and reference for the C++ Standard Library. The second edition (released on April 9, 2012) covers C++11. [Review]

  • The C++ IO Streams and Locales (Angelika Langer and Klaus Kreft) There's very little to say about this book except that, if you want to know anything about streams and locales, then this is the one place to find definitive answers. [Review]

C++11/14 References:

  • The C++ Standard (INCITS/ISO/IEC 14882-2011) This, of course, is the final arbiter of all that is or isn't C++. Be aware, however, that it is intended purely as a reference for experienced users willing to devote considerable time and effort to its understanding. As usual, the first release was quite expensive ($300+ US), but it has now been released in electronic form for $60US.

  • The C++14 standard is available, but seemingly not in an economical form – directly from the ISO it costs 198 Swiss Francs (about $200 US). For most people, the final draft before standardization is more than adequate (and free). Many will prefer an even newer draft, documenting new features that are likely to be included in C++17.

  • Overview of the New C++ (C++11/14) (PDF only) (Scott Meyers) (updated for C++1y/C++14) These are the presentation materials (slides and some lecture notes) of a three-day training course offered by Scott Meyers, who's a highly respected author on C++. Even though the list of items is short, the quality is high.

  • The C++ Core Guidelines (C++11/14/17/…) (edited by Bjarne Stroustrup and Herb Sutter) is an evolving online document consisting of a set of guidelines for using modern C++ well. The guidelines are focused on relatively higher-level issues, such as interfaces, resource management, memory management and concurrency affecting application architecture and library design. The project was announced at CppCon'15 by Bjarne Stroustrup and others and welcomes contributions from the community. Most guidelines are supplemented with a rationale and examples as well as discussions of possible tool support. Many rules are designed specifically to be automatically checkable by static analysis tools.

  • The C++ Super-FAQ (Marshall Cline, Bjarne Stroustrup and others) is an effort by the Standard C++ Foundation to unify the C++ FAQs previously maintained individually by Marshall Cline and Bjarne Stroustrup and also incorporating new contributions. The items mostly address issues at an intermediate level and are often written with a humorous tone. Not all items might be fully up to date with the latest edition of the C++ standard yet.

  • cppreference.com (C++03/11/14/17/…) (initiated by Nate Kohl) is a wiki that summarizes the basic core-language features and has extensive documentation of the C++ standard library. The documentation is very precise but is easier to read than the official standard document and provides better navigation due to its wiki nature. The project documents all versions of the C++ standard and the site allows filtering the display for a specific version. The project was presented by Nate Kohl at CppCon'14.


Classics / Older

Note: Some information contained within these books may not be up-to-date or no longer considered best practice.

  • The Design and Evolution of C++ (Bjarne Stroustrup) If you want to know why the language is the way it is, this book is where you find answers. This covers everything before the standardization of C++.

  • Ruminations on C++ - (Andrew Koenig and Barbara Moo) [Review]

  • Advanced C++ Programming Styles and Idioms (James Coplien) A predecessor of the pattern movement, it describes many C++-specific “idioms”. It's certainly a very good book and might still be worth a read if you can spare the time, but quite old and not up-to-date with current C++.

  • Large Scale C++ Software Design (John Lakos) Lakos explains techniques to manage very big C++ software projects. Certainly a good read, if it only was up to date. It was written long before C++98, and misses on many features (e.g. namespaces) important for large scale projects. If you need to work in a big C++ software project, you might want to read it, although you need to take more than a grain of salt with it. The first volume of a new edition is expected in 2015.

  • Inside the C++ Object Model (Stanley Lippman) If you want to know how virtual member functions are commonly implemented and how base objects are commonly laid out in memory in a multi-inheritance scenario, and how all this affects performance, this is where you will find thorough discussions of such topics.

  • The Annotated C++ Reference Manual (Bjarne Stroustrup, Margaret A. Ellis) This book is quite outdated in the fact that it explores the 1989 C++ 2.0 version - Templates, exceptions, namespaces and new casts were not yet introduced. Saying that however, this book goes through the entire C++ standard of the time explaining the rationale, the possible implementations and features of the language. This is not a book to learn programming principles and patterns on C++, but to understand every aspect of the C++ language.

by anonymous   2017-08-20
char* found = std::find(arr, arr+9, ' ');

Note that 'no match' is signaled wuth the end iterator:

bool match = (arr+9) != found;

Note, that

  • binary search doesn't apply unless you characters are in some known ordering.
  • std::find is inlined, templatized and will perform to the max if you turn on optimization (e.g. -O3 -march=native for g++)

Edit since you have shown more code, I now realize you actually want to detect (sub)string length. You could use

Of course, that assumes you'd want to convert the char[] to std::string for the purpose. In practice, that might be a perfectly valid idea, because of SSO (Small String Optimization) found in nearly all implementations of the C++ standard library. (see Items 13-16 in Herb Sutter's More Exceptional C++, or Scott Meyers' discussion of commercial std::string implementations in Effective STL).

by anonymous   2017-08-20

I was in the same situation 12 years ago when I got my first programming job out of college. I didn't do any open source but I managed to gain a lot of practical and advanced C++ knowledge by reading books (the dead tree kind).

In particular, there was an excellent series by Scott Meyers which I feel helped the most in turning me from newbie to professional:

Effective C++: 55 Specific Ways to Improve Your Programs and Designs

More Effective C++: 35 New Ways to Improve Your Programs and Designs

Effective STL: 50 Specific Ways to Improve Your Use of the Standard Template Library

The topics in these books range from beginner to advanced. It took me about 2 years working in C++ to understand every chapter in these books, so don't be disheartened if it goes over your head at some point... just try reading it again later :)

by anonymous   2017-08-20

The reason for the error is that you are calling the copy constructor of auto_ptr my_player in fooPlayerFactory::MakePlayerO() which is a const method. That means that is cannot modify its members.

However the copy constructor of auto_ptr DOES modify the right hand side so returning my_player trys to change its pointer to 0 (NULL), while assigning the original pointer to the auto_ptr in the return value.

The signature of the copy constuctor is

auto_ptr<T>::auto_ptr<T>(auto_ptr<T> & rhs)

not

auto_ptr<T>::auto_ptr<T>(const auto_ptr<T> & rhs)

The copy constructor of auto_ptr assigns ownership of the pointer to the left hand side, the right hand side then holds nothing.

I don't think you want to use auto_ptr here, you probably want boost::smart_ptr

It looks like you have mixed up two uses for auto_ptr

The first is as poor man's boost::scoped_ptr. This is to manage a single instance of a pointer in a class, the class manages the life time of the pointer. In this case you don't normally return this pointer outside your class (you can it is legal, but boost::smart_ptr / boost::weak_ptr would be better so clients can participate the life time of the pointer)

The second is its main purpose which is to return a newly created pointer to the caller of a function in an exception safe way.

eg

auto_ptr<T> foo() {
    return new T;
}

void bar() {
    auto_ptr<T> t = foo();
}

As I said I think you have mixed these two uses auto_ptr is a subtle beast you should read the auto_ptr docs carefully. It is also covered very well in Effective STL by Scott Meyers.