Tutorials - The Static Keyword in C++ Most C++ keywords allow you to do one thing. You use int to declare an int, or that a function returns an int or expects an int as an argument. You use new to allocate memory, and delete to free memory. You use const to indicate that a variable's value cannot be changed. Ironically, the keyword static, though the word means "unchanging," has multiple (and apparently unrelated) uses. The keyword static can be used in three major contexts: inside a function, inside a class definition, and in front of a global variable inside a file making up a multifile program. The use of static inside a function is the simplest. You can also use static in this fashion to prevent a variable from being reinitialized inside a loop. For(int x=0; x<10; x++) { for(int y=0; y<10; y++) { static int number_of_times = 0; number_of_times++; } } The second use of static is inside a class definition. You can also have static member functions of a class.
For instance, you could use the following code: The line. Keyword - When to use friend class in c++ Inheritance - Why does C++ not allow inherited friendship. C/C++ private array initialization in the header file. Tech Talk about C++ Templates / Comeau C++ Template FAQ. Copyright © 2000-2008 Comeau Computing. All rights reserved. Note that this is a live web page, in the sense that we'll be adding new discussions as appropriate, so stop by from time to time.
This web page is evolving (Version 1.6, August 6, 2008), so if you see something not right, or have a question that is appropriate (note this FAQ is not a templates tutorial) please email us about it. . We don't recommend book. Note that we've broken our list down into categories, consider getting one or two from each category. Note that often there is a problem between technical accuracy and readability. Categorically, we have not been satisfied with online tutorials (this does not mean that there are no good ones, just that we have not seen it yet). In general, if you need a FAQ, check out The question is: What is being modified? Struct SomeClass { int i; }; whereas this is clearly a template: template <typename T> struct cTemplate { int member; }; What kind of template is it? C++ Programming/RTTI. Run-Time Type Information (RTTI)[edit] RTTI refers to the ability of the system to report on the dynamic type of an object and to provide information about that type at runtime (as opposed to at compile time), when utilized consistently can be a powerful tool to ease the work of the programmer in managing resources. dynamic_cast[edit] Consider what you have already learned about the dynamic_cast keyword and let's say that we have the following class hierarchy: Let's say that we also have a pointer of type Interface*, like so: Interface* ptr_interface; Supposing that a situation emerges that we are forced to presume but have no guarantee that the pointer points to an object of type SpecificClass and we would like to call the member SpecificOp() of that class.
To dynamically convert to a derived type we can use dynamic_cast, like so: With dynamic_cast, the program converts the base class pointer to a derived class pointer and allows the derived class members to be called. Typeid[edit] Syntax. Determining the Size of Class Objects. By Girish Shetty There are many factors that decide the size of an object of a class in C++.
These factors are: Size of all non-static data members Order of data members Byte alignment or byte padding Size of its immediate base class The existence of virtual function(s) (Dynamic polymorphism using virtual functions). Compiler being used Mode of inheritance (virtual inheritance) Size of all non-static data members Only non-static data members will be counted for calculating sizeof class/object. For an object of class A, the size will be the size of float iMem1 + size of int iMem2 + size of char iMem4. Class C { char c; int int1; int int2; int i; long l; short s; }; The size of this class is 24 bytes. If I re-write the above class in different order, keeping all my data members like below: class C { int int1; int int2; int i; long l; short s; char c; }; Now the size of this class is 20 bytes. In this case, it is storing c, the char, in one of the slots in the hole in the extra four bytes.
The C++ 'const' Declaration: Why & How. The 'const' system is one of the really messy features of C++. It is simple in concept: variables declared with ‘const’ added become constants and cannot be altered by the program. However it is also used to bodge in a substitute for one of the missing features of C++ and there it gets horridly complicated and sometimes frustratingly restrictive. The following attempts to explain how 'const' is used and why it exists. Simple Use of ‘const’ The simplest use is to declare a named constant. This was available in the ancestor of C++, C. To do this, one declares a constant as if it was a variable but add ‘const’ before it. Const int Constant1=96; will create an integer constant, unimaginatively called ‘Constant1’, with the value 96. Such constants are useful for parameters which are used in the program but do not need to be changed after the program is compiled. Const int * Constant2 declares that Constant2 is a variable pointer to a constant integer and int const * Constant2 int * const Constant3.
C++ - Inheriting from a template class, using a type defined in the derived class. C++ - Nested templates with dependent scope. A Quick Look at References and Constants. Use struct to create a boolean type. Algorithm Tutorials. The Best Questions for Would-be C++ Programmers, Part 1 It seems that an almost obligatory and very important part of the recruitment process is "the test. " "The test" can provide information both for the interviewer and the candidate. The interviewer is provided with a means to test the candidate's practical know-how and particular programming language understanding; the candidate can get an indication of the technologies used for the job and the level of proficiency the company expects and even decide if he still wants (and is ready for) the job in question. I've had my fair share of interviews, more or less successful, and I would like to share with you my experience regarding some questions I had to face.
I also asked for feedback from three of the top rated TopCoder members: bmerry , kyky and sql_lall , who were kind enough to correct me where I was not accurate (or plain wrong) and suggest some other questions (that I tried to answer to my best knowledge). References. Algorithm Tutorials. The Best Questions for Would-be C++ Programmers, Part 2 ... read Part 1 In the second part of this installment we'll tackle some questions regarding more advanced features of the language (the experienced C++ programmers will consider some of these more on the basic side). So let's get to it and work on the second part of this "interview". That was it, folks! I hope that even if those questions did not pose any challenges, you still had fun doing/reading this quiz and refreshing your memory on some aspects of the C++ language.
Good luck on those interviews! Notes (**) The compiler does all the magic: first, for each class that contains virtual functions (base and derived), the compiler creates a static table called the VTABLE. (***) For that and other fine C++ gems go to Stroustrup. References [1] Bjarne Stroustrup - The C++ Programming Language Special 3rd Edition [2] Stanley B. Copy constructor. Definition[edit] X(const X& copy_from_me); X(X& copy_from_me); X(volatile X& copy_from_me); X(const volatile X& copy_from_me); X(X& copy_from_me, int = 0); X(const X& copy_from_me, double = 1.0, int = 42); ...
The first one should be used unless there is a good reason to use one of the others. One of the differences between the first and the second is that temporaries can be copied with the first. For example: X a = X(); // valid given X(const X& copy_from_me) but not valid given X(X& copy_from_me) // because the second wants a non-const X& // to create a, the compiler first creates a temporary by invoking the default constructor // of X, then uses the copy constructor to initialize as a copy of that temporary. // For some compilers both versions actually work but this behaviour should not be relied // upon because it's non-standard.
Another difference between them is the obvious: The X& form of the copy constructor is used when it is necessary to modify the copied object. Operation[edit] Using Namespaces in C. One of C++'s less heralded additions is addition of namespaces, which can be used to structure a program into "logical units".
A namespace functions in the same way that a company division might function -- inside a namespace you include all functions appropriate for fulfilling a certain goal. For instance, if you had a program that connected to the Internet, you might have a namespace to handle all connection functions: namespace net_connect { int make_connection(); int test_connection(); //so forth... } You can then refer to functions that are part of a namespace by prefixing the function with the namespace name followed by the scope operator -- ::. For instance, net_connect::make_connection() By enabling this program structure, C++ makes it easier for you to divide up a program into groups that each perform their own separate functions, in the same way that classes or structs simplify object oriented design.
Using namespace namespace_name; using namespace std; using namespace_name::thing; Strcspn. Const Correctness Question in C++ Constant data members. Jan 5, 2009 at 4:50pm Jan 5, 2009 at 3:50pm UTC Can data members be constant (with const) so that they are given a value by the constructor and them cannot be changed? If yes, can a data member be static const? (I'm asking the second question because a static member is defined outside the class while constant variables have to be defined and declared in one line) Jan 5, 2009 at 5:23pm Jan 5, 2009 at 4:23pm UTC Thanks for the answer, but in the example a static const variable is defined inside the class!
Jan 5, 2009 at 10:54pm Jan 5, 2009 at 9:54pm UTC The tutorial was talking about static members, not about static const integral members Last edited on Jan 5, 2009 at 10:54pm Jan 6, 2009 at 3:06pm Jan 6, 2009 at 2:06pm UTC Thanks for the answers. Last edited on Jan 6, 2009 at 3:49pm Jan 6, 2009 at 2:49pm UTC Jan 6, 2009 at 3:51pm Jan 6, 2009 at 2:51pm UTC But what about a static const non-integral member?
Jan 6, 2009 at 5:02pm Jan 6, 2009 at 4:02pm UTC Jan 7, 2009 at 3:58pm Jan 7, 2009 at 2:58pm UTC. Tutorial: Pointers in C and C++ Using Variables Essentially, the computer's memory is made up of bytes. Each byte has a number, an address, associated with it. The picture below represents several bytes of a computer's memory. In the picture, addresses 924 thru 940 are shown. Try: C Code Listing 1 C++ Code Listing 1 At line (4) in the program above, the computer reserves memory for fl. When fl is used in line (5), two distinct steps occur: The program finds and grabs the address reserved for fl--in this example 924.
To generalize, whenever any variable is accessed, the above two distinct steps occur to retrieve the contents of the variable. Separating the Steps Two operators are provided that, when used, cause these two steps to occur separately. Try this code to see what prints out: C Code Listing 2 C++ Code Listing 2 On line (5) of the example, The & operator is being used on fl. 1. It is fl's address that is printed to the screen. Keep in mind that an address is really just a simple number. C Code Listing 3 C++ Code Listing 3. [SOLVED] Extern String Variable - C And C++ 8.12 — Static member functions. In the previous lesson on static member variables, you learned that classes can have member variables that are shared across all objects of that class type. However, what if our static member variables are private?
Consider the following example: In this case, we can’t access Something::s_nValue directly from main(), because it is private. Normally we access private members through public member functions. Like static member variables, static member functions are not attached to any particular object. Because static member functions are not attached to a particular object, they can be called directly by using the class name and the scope operator.
Static member functions have two interesting quirks worth noting. Second, static member functions can only access static member variables. Here’s another example using static member variables and functions: This program prints: The next ID is: 1 The next ID is: 2 The next ID is: 3 The next ID is: 4 The next ID is: 5. Set pointer to null through function.
C++ - Why can't I have a non-integral static const member in a class. C++ - What is the difference between exit() and abort() An odd C++ error: test.cpp:15: error: passing ‘const *’ as ‘this’ argument of ‘*’ discards qualifiers. C++ Tutorial - Lesson 22: Mutable Members. Assert. If the argument expression of this macro with functional form compares equal to zero (i.e., the expression is false), a message is written to the standard error device and abort is called, terminating the program execution. The specifics of the message shown depend on the particular library implementation, but it shall at least include: the whose assertion failed, the name of the source file, and the line number where it happened.
A usual expression format is: Assertion failed: expression, file filename, line line number This macro is disabled if, at the moment of including <assert.h>, a macro with the name NDEBUG has already been defined. This allows for a coder to include as many assert calls as needed in a source code while debugging the program and then disable all of them for the production version by simply including a line like: at the beginning of its code, before the inclusion of <assert.h>. Exit code - How to quit a C++ program.