c++

Difference between ‘struct’ and ‘typedef struct’ in C++?

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In C++, there is only a subtle difference. It’s a holdover from C, in which it makes a difference. The C language standard (C89 §3.1.2.3, C99 §6.2.3, and C11 §6.2.3) mandates separate namespaces for different categories of identifiers, including tag identifiers (for struct/union/enum) and ordinary identifiers (for typedef and other identifiers). If you just said: … Read more

How to convert an instance of std::string to lower case

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Adapted from Not So Frequently Asked Questions: #include <algorithm> #include <cctype> #include <string> std::string data = “Abc”; std::transform(data.begin(), data.end(), data.begin(), [](unsigned char c){ return std::tolower(c); }); You’re really not going to get away without iterating through each character. There’s no way to know whether the character is lowercase or uppercase otherwise. If you really hate … Read more

What is std::move(), and when should it be used?

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1. “What is it?” While std::move() is technically a function – I would say it isn’t really a function. It’s sort of a converter between ways the compiler considers an expression’s value. 2. “What does it do?” The first thing to note is that std::move() doesn’t actually move anything. It changes an expression from being … Read more

How to trim a std::string?

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EDIT Since c++17, some parts of the standard library were removed. Fortunately, starting with c++11, we have lambdas which are a superior solution. #include <algorithm> #include <cctype> #include <locale> // trim from start (in place) static inline void ltrim(std::string &s) { s.erase(s.begin(), std::find_if(s.begin(), s.end(), [](unsigned char ch) { return !std::isspace(ch); })); } // trim from … Read more

Why should C++ programmers minimize use of ‘new’?

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There are two widely-used memory allocation techniques: automatic allocation and dynamic allocation. Commonly, there is a corresponding region of memory for each: the stack and the heap. Stack The stack always allocates memory in a sequential fashion. It can do so because it requires you to release the memory in the reverse order (First-In, Last-Out: … Read more

What does T&& (double ampersand) mean in C++11?

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It declares an rvalue reference (standards proposal doc). Here’s an introduction to rvalue references. Here’s a fantastic in-depth look at rvalue references by one of Microsoft’s standard library developers. CAUTION: the linked article on MSDN (“Rvalue References: C++0x Features in VC10, Part 2”) is a very clear introduction to Rvalue references, but makes statements about … Read more

What are the new features in C++17?

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Language features: Templates and Generic Code Template argument deduction for class templates Like how functions deduce template arguments, now constructors can deduce the template arguments of the class http://wg21.link/p0433r2 http://wg21.link/p0620r0 http://wg21.link/p0512r0 template <auto> Represents a value of any (non-type template argument) type. Non-type template arguments fixes template<template<class…>typename bob> struct foo {} ( Folding + … … Read more

What are the rules about using an underscore in a C++ identifier?

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The rules (which did not change in C++11): Reserved in any scope, including for use as implementation macros: identifiers beginning with an underscore followed immediately by an uppercase letter identifiers containing adjacent underscores (or “double underscore”) Reserved in the global namespace: identifiers beginning with an underscore Also, everything in the std namespace is reserved. (You … Read more