A functor is pretty much just a class which defines the operator(). That lets you create objects which “look like” a function: // this is a functor struct add_x { add_x(int val) : x(val) {} // Constructor int operator()(int y) const { return x + y; } private: int x; }; // Now you can … Read more
If you just want to pass a std::string to a function that needs const char* you can use std::string str; const char * c = str.c_str(); If you want to get a writable copy, like char *, you can do that with this: std::string str; char * writable = new char[str.size() + 1]; std::copy(str.begin(), str.end(), … Read more
C++98 and C++03 This answer is for the older versions of the C++ standard. The C++11 and C++14 versions of the standard do not formally contain ‘sequence points’; operations are ‘sequenced before’ or ‘unsequenced’ or ‘indeterminately sequenced’ instead. The net effect is essentially the same, but the terminology is different. Disclaimer : Okay. This answer … Read more
In addition to what visitor said : The function void emplace_back(Type&& _Val) provided by MSCV10 is non conforming and redundant, because as you noted it is strictly equivalent to push_back(Type&& _Val). But the real C++0x form of emplace_back is really useful: void emplace_back(Args&&…); Instead of taking a value_type it takes a variadic list of arguments, … Read more
C++11: Yes! C++11 and onwards has this same feature (called delegating constructors). The syntax is slightly different from C#: class Foo { public: Foo(char x, int y) {} Foo(int y) : Foo(‘a’, y) {} }; C++03: No Unfortunately, there’s no way to do this in C++03, but there are two ways of simulating this: You … Read more
Case statements are only labels. This means the compiler will interpret this as a jump directly to the label. In C++, the problem here is one of scope. Your curly brackets define the scope as everything inside the switch statement. This means that you are left with a scope where a jump will be performed … Read more
gcc and g++ are compiler-drivers of the GNU Compiler Collection (which was once upon a time just the GNU C Compiler). Even though they automatically determine which backends (cc1 cc1plus …) to call depending on the file-type, unless overridden with -x language, they have some differences. The probably most important difference in their defaults is … Read more
Let’s get pedantic, because there are differences that can actually affect your code’s behavior. Much of the following is taken from comments made to an “Old New Thing” article. Sometimes the memory returned by the new operator will be initialized, and sometimes it won’t depending on whether the type you’re newing up is a POD … Read more
How can it be? Isn’t the memory of a local variable inaccessible outside its function? You rent a hotel room. You put a book in the top drawer of the bedside table and go to sleep. You check out the next morning, but “forget” to give back your key. You steal the key! A week … Read more
They are equivalent, from the standard (emphasis mine) (7.1.3.2): A typedef-name can also be introduced by an alias-declaration. The identifier following the using keyword becomes a typedef-name and the optional attribute-specifier-seq following the identifier appertains to that typedef-name. It has the same semantics as if it were introduced by the typedef specifier. In particular, it … Read more