Read it backwards (as driven by Clockwise/Spiral Rule): int* – pointer to int int const * – pointer to const int int * const – const pointer to int int const * const – const pointer to const int Now the first const can be on either side of the type so: const int * … Read more
The problem C++ includes useful generic functions like std::for_each and std::transform, which can be very handy. Unfortunately they can also be quite cumbersome to use, particularly if the functor you would like to apply is unique to the particular function. #include <algorithm> #include <vector> namespace { struct f { void operator()(int) { // do something … Read more
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 (introducing new-line characters … Read more
No, it will not be faster on most architectures. You didn’t specify, but on x86, all of the integral comparisons will be typically implemented in two machine instructions: A test or cmp instruction, which sets EFLAGS And a Jcc (jump) instruction, depending on the comparison type (and code layout): jne – Jump if not equal … Read more
Virtual destructors are useful when you might potentially delete an instance of a derived class through a pointer to base class: class Base { // some virtual methods }; class Derived : public Base { ~Derived() { // Do some important cleanup } }; Here, you’ll notice that I didn’t declare Base’s destructor to be … Read more
It’s very unfortunate that you see dynamic allocation so often. That just shows how many bad C++ programmers there are. In a sense, you have two questions bundled up into one. The first is when should we use dynamic allocation (using new)? The second is when should we use pointers? The important take-home message is … Read more
An alternative approach would be to extract features (keypoints) using the scale-invariant feature transform (SIFT) or Speeded Up Robust Features (SURF). You can find a nice OpenCV code example in Java, C++, and Python on this page: Features2D + Homography to find a known object Both algorithms are invariant to scaling and rotation. Since they … Read more
static_cast static_cast is used for cases where you basically want to reverse an implicit conversion, with a few restrictions and additions. static_cast performs no runtime checks. This should be used if you know that you refer to an object of a specific type, and thus a check would be unnecessary. Example: void func(void *data) { … Read more
C++11 introduces std::stoi (and variants for each numeric type) and std::to_string, the counterparts of the C atoi and itoa but expressed in term of std::string. #include <string> std::string s = std::to_string(42); is therefore the shortest way I can think of. You can even omit naming the type, using the auto keyword: auto s = std::to_string(42); … Read more
I find it easiest to understand move semantics with example code. Let’s start with a very simple string class which only holds a pointer to a heap-allocated block of memory: #include <cstring> #include <algorithm> class string { char* data; public: string(const char* p) { size_t size = std::strlen(p) + 1; data = new char[size]; std::memcpy(data, … Read more