c++-faq

问题 This answer of @R. Martinho Fernandes shows, that the safe-bool idiom is apperently deprecated in C++11, as it can be replaced by a simple explicit operator bool() const; according to the standard quote in the answer §4 [conv] p3 : An expression e can be implicitly converted to a type T if and only if the declaration T t=e; is well-formed, for some invented temporary variable t (§8.5). Certain language constructs require that an expression be converted to a Boolean value. An expression e

问题 This answer of @R. Martinho Fernandes shows, that the safe-bool idiom is apperently deprecated in C++11, as it can be replaced by a simple explicit operator bool() const; according to the standard quote in the answer §4 [conv] p3 : An expression e can be implicitly converted to a type T if and only if the declaration T t=e; is well-formed, for some invented temporary variable t (§8.5). Certain language constructs require that an expression be converted to a Boolean value. An expression e

问题 I heard a few people recommending to use enum classes in C++ because of their type safety . But what does that really mean? 回答1: C++ has two kinds of enum : enum class es Plain enum s Here are a couple of examples how to declare them: enum class Color { red, green, blue }; // enum class enum Animal { dog, cat, bird, human }; // plain enum What is the difference between two? enum class es - enumerator names are local to the enum and their values do not implicitly convert to other types (like

问题 What are undefined reference/unresolved external symbol errors? What are common causes and how to fix/prevent them? Feel free to edit/add your own. 回答1: Compiling a C++ program takes place in several steps, as specified by 2.2 (credits to Keith Thompson for the reference): The precedence among the syntax rules of translation is specified by the following phases [see footnote] . Physical source file characters are mapped, in an implementation-defined manner, to the basic source character set

问题 C++17 will add copy capture of this object by value, with a capture specification of [*this]. How is this useful? How is it different than capturing this ? Can't this already be achieved in C++14 with [tmp = *this] ? Bonus for explaining why P0018R3 uses [=, tmp = *this] instead of [tmp = *this] in their example. If they had used [tmp = *this] , all the listed downsides of the C++14 solution would be eliminated. 回答1: How is it useful? It's useful when you need a copy of *this - for example,

问题 I keep seeing reference to both the C++ standard Library and the C++ Standard Template Library (STL). What is the difference between them? Wikipedia mentions that they share some headers but that's about it. 回答1: The Standard Template Library (STL) is a library of containers, iterators, algorithms, and function objects, that was created by Alexander Stepanov; the SGI website has the canonical implementation and documentation. The standard library is the library that is part of C++; it

问题 This is a problem I come across often. The following examples illustrates it: struct A { int m_SomeNumber; }; struct B { B( A & RequiredObject ); private: A & m_RequiredObject; }; struct C { C( ); private: A m_ObjectA; B m_ObjectB; }; The implementation of the constructor of C looks something like this: C::C( ) : B( m_ObjectA ) { } Since the order of initialization is not defined, m_ObjectA might be uninitialized when the constructor of m_ObjectB is called, resulting in undefined behavior.

问题 This is a problem I come across often. The following examples illustrates it: struct A { int m_SomeNumber; }; struct B { B( A & RequiredObject ); private: A & m_RequiredObject; }; struct C { C( ); private: A m_ObjectA; B m_ObjectB; }; The implementation of the constructor of C looks something like this: C::C( ) : B( m_ObjectA ) { } Since the order of initialization is not defined, m_ObjectA might be uninitialized when the constructor of m_ObjectB is called, resulting in undefined behavior.

问题 Are the stages of compilation of a C++ program specified by the standard? If so, what are they? If not, an answer for a widely-used compiler (I'd prefer MSVS) would be great. I'm talking about preprocessing, tokenization, parsing and such. What is the order in which they are executed and what do they do in particular? EDIT: I know what compilation, linking and preprocessing do, I'm mostly interested in the others and the order. Explanations for these are, of course, also welcomed since I

问题 What is SFINAE in C++? Can you please explain it in words understandable to a programmer who is not versed in C++? Also, what concept in a language like Python does SFINAE correspond to? 回答1: Warning: this is a really long explanation, but hopefully it really explains not only what SFINAE does, but gives some idea of when and why you might use it. Okay, to explain this we probably need to back up and explain templates a bit. As we all know, Python uses what's commonly referred to as duck