The class declaration should be in the header file (Or in the source file if not shared). File: foo.h class foo { private: static int i; }; But the initialization should be in source file. File: foo.cpp int foo::i = 0; If the initialization is in the header file then each file that includes the … Read more
Several reasons Header files Every single compilation unit requires hundreds or even thousands of headers to be (1) loaded and (2) compiled. Every one of them typically has to be recompiled for every compilation unit, because the preprocessor ensures that the result of compiling a header might vary between every compilation unit. (A macro may … Read more
Yes, with SFINAE you can check if a given class does provide a certain method. Here’s the working code: #include <iostream> struct Hello { int helloworld() { return 0; } }; struct Generic {}; // SFINAE test template <typename T> class has_helloworld { typedef char one; struct two { char x[2]; }; template <typename C> … Read more
Stan Lippman talked about this here. I thought it was interesting. Summary: Stroustrup originally used class to specify types in templates to avoid introducing a new keyword. Some in the committee worried that this overloading of the keyword led to confusion. Later, the committee introduced a new keyword typename to resolve syntactic ambiguity, and decided … Read more
The C++ Standard reads in section 7.3.1.1 Unnamed namespaces, paragraph 2: The use of the static keyword is deprecated when declaring objects in a namespace scope, the unnamed-namespace provides a superior alternative. Static only applies to names of objects, functions, and anonymous unions, not to type declarations. Edit: The decision to deprecate this use of … Read more
If your row length is a compile time constant, C++11 allows auto arr2d = new int [nrows][CONSTANT]; See this answer. Compilers like gcc that allow variable-length arrays as an extension to C++ can use new as shown here to get fully runtime-variable array dimension functionality like C99 allows, but portable ISO C++ is limited to … Read more
Undefined behavior is one of those aspects of the C and C++ language that can be surprising to programmers coming from other languages (other languages try to hide it better). Basically, it is possible to write C++ programs that do not behave in a predictable way, even though many C++ compilers will not report any … Read more
Be extremely careful using any of the other suggestions. It all depends on context. I have spent a long time tracing bugs in a system that presumed a==b if |a-b|<epsilon. The underlying problems were: The implicit presumption in an algorithm that if a==b and b==c then a==c. Using the same epsilon for lines measured in … Read more
C++ has two kinds of enum: enum classes Plain enums Here are a couple of examples on 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 the two? enum classes – enumerator names … Read more
argv and argc are how command line arguments are passed to main() in C and C++. argc will be the number of strings pointed to by argv. This will (in practice) be 1 plus the number of arguments, as virtually all implementations will prepend the name of the program to the array. The variables are … Read more