So you can write code like this: void f( const string & s ) { } f( “foobar” ); Although strictly speaking what is actually happening here is not the literal being bound to a const reference – instead a temprary string object is created: string( “foobar” ); and this nameless string is bound to … Read more
Not so hard: A x; A * p = new A; These two are default initialization. Since you don’t have a user-defined constructor, this just means that all members are default-initialized. Default-initializing a fundamental type like int means “no initialization”. Next: A * p = new A(); This is value initialization. (I don’t think there … Read more
Non-static methods are instance methods. This are only accessible in existing instance, and instance does not exist yet when you are in constructor (it is still under construction). Why it is so? Because instance methods can access instance (non-static) fields, which can have different values in different instances, so it doesn’t make sense to call … Read more
The use of NS_DESIGNATED_INITIALIZER is nicely explained in http://useyourloaf.com/blog/2014/08/19/xcode-6-objective-c-modernization.html: The designated initializer guarantees the object is fully initialised by sending an initialization message to the superclass. The implementation detail becomes important to a user of the class when they subclass it. The rules for designated initializers in detail: A designated initializer must call (via super) … Read more
The zero initialization is specified in the standard as default zero initialization/value initialization for builtin types, primarily to support just this type of case in template use. Note that this behavior is different from a local variable such as int x; which leaves the value uninitialized (as in the C language that behavior is inherited … Read more
Yes, they are initialized in the order in which they appear in the source. You can read all of the gory details in The Java Language Specification, ยง12.4.2. See step 9, which reads: … execute either the class variable initializers and static initializers of the class, or the field initializers of the interface, in textual … Read more
The const variable specifies whether a variable is modifiable or not. The constant value assigned will be used each time the variable is referenced. The value assigned cannot be modified during program execution. Bjarne Stroustrup’s explanation sums it up briefly: A class is typically declared in a header file and a header file is typically … Read more
Just to clarify something that came up in some of the other answers… There is no requirement that the initializer list be in either the source (.cpp) or header (.h) file. In fact, the compiler does not distinguish between the two types of files. The important distinction is between the contructor’s declaration and it’s definition. … Read more
It depends on the order of data member declarations in the class. So a_ will be the first one, then b_ will be the second one in your example.
For POD data members, it makes no difference, it’s just a matter of style. For class members which are classes, then it avoids an unnecessary call to a default constructor. Consider: class A { public: A() { x = 0; } A(int x_) { x = x_; } int x; }; class B { public: … Read more