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C++ Programming Code Examples

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Constructor and destructor inside a struct

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/* Constructor and destructor inside a struct */ #include <iostream> #include <cstring> #include <cstdlib> using namespace std; struct StringClass { StringClass(char *ptr); ~StringClass(); void show(); private: char *p; int len; }; StringClass::StringClass(char *ptr) { len = strlen(ptr); p = (char *) malloc(len+1); if(!p) { cout << "Allocation error\n"; exit(1); } strcpy(p, ptr); } StringClass::~StringClass() { cout << "Freeing p\n"; free(p); } void StringClass::show() { cout << p << " - length: " << len; cout << endl; } int main() { StringClass stringObject1("Hello World"), stringObject2("Hello World"); stringObject1.show(); stringObject2.show(); return 0; }
Standard Library malloc() Function in C++
Allocate memory block. Allocates a block of size bytes of memory, returning a pointer to the beginning of the block. The content of the newly allocated block of memory is not initialized, remaining with indeterminate values. If size is zero, the return value depends on the particular library implementation (it may or may not be a null pointer), but the returned pointer shall not be dereferenced. Malloc function in C++ is used to allocate a specified size of the block of memory dynamically uninitialized. It allocates the memory to the variable on the heap and returns the void pointer pointing to the beginning address of the memory block. The values in the memory block allocated remain uninitialized and indeterminate. In case the size specified in the function is zero then pointer returned must not be dereferenced as it can be a null pointer, and in this case, behavior depends on particular library implementation. When a memory block is allocated dynamically memory is allocated on the heap but the pointer is allocated to the stack.
Syntax for malloc() Function in C++
#include <cstdlib> void* malloc (size_t size);
size
Size of the memory block, in bytes. size_t is an unsigned integral type. On success, a pointer to the memory block allocated by the function. The type of this pointer is always void*, which can be cast to the desired type of data pointer in order to be dereferenceable. If the function failed to allocate the requested block of memory, a null pointer is returned.
Advantages of malloc() in C++
There are a lot of advantages to using the malloc method in one's application: • Dynamic Memory allocation: Usually we create arrays at compile time in C++, the size of such arrays is fixed. In the case at run time we do not use all the space or extra space is required for more elements to be inserted in the array, then this leads to improper memory management or segmentation fault error. • Heap memory: Local arrays that are defined at compile time are allocated on the stack, which has lagged in memory management in case the number of data increases. Thus one needs to allocate memory out of the stack, thus malloc comes into the picture as it allocates the memory location on the heap and returns a pointer on the stack pointing to the starting address of the array type memory being allocated. • Variable-length array: This function helps to allocate memory for an array whose size can be defined at the runtime. Thus one can create the number of blocks as much as required at run time. • Better lifetime: Variable created using malloc method is proved to have a better life than the local arrays as a lifetime of local arrays depends on the scope they are being defined and cannot access out of their scope. But variables or arrays created using malloc exist till they are freed. This is of great importance for various data structures such as linked list, binary heap, etc.
Differences between the malloc() and new
• The new operator constructs an object, i.e., it calls the constructor to initialize an object while malloc() function does not call the constructor. The new operator invokes the constructor, and the delete operator invokes the destructor to destroy the object. This is the biggest difference between the malloc() and new. • The new is an operator, while malloc() is a predefined function in the stdlib header file. • The operator new can be overloaded while the malloc() function cannot be overloaded. • If the sufficient memory is not available in a heap, then the new operator will throw an exception while the malloc() function returns a NULL pointer. • In the new operator, we need to specify the number of objects to be allocated while in malloc() function, we need to specify the number of bytes to be allocated. • In the case of a new operator, we have to use the delete operator to deallocate the memory. But in the case of malloc() function, we have to use the free() function to deallocate the memory.
Data races
Only the storage referenced by the returned pointer is modified. No other storage locations are accessed by the call. If the function reuses the same unit of storage released by a deallocation function (such as free or realloc), the functions are synchronized in such a way that the deallocation happens entirely before the next allocation.
Exceptions
No-throw guarantee: this function never throws exceptions.
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/* allocate the requested size of bytes and it returns a pointer to the first byte of allocated memory by malloc() function code example. */ #include <iostream> #include <cstdlib> using namespace std; int main() { // allocate 5 int memory blocks int* ptr = (int*) malloc(5 * sizeof(int)); // check if memory has been allocated successfully if (!ptr) { cout << "Memory Allocation Failed"; exit(1); } cout << "Initializing values..." << endl << endl; for (int i = 0; i < 5; i++) { ptr[i] = i * 2 + 1; } cout << "Initialized values" << endl; // print the values in allocated memories for (int i = 0; i < 5; i++) { // ptr[i] and *(ptr+i) can be used interchangeably cout << *(ptr + i) << endl; } // deallocate memory free(ptr); return 0; }
#include Directive in C++
#include is a way of including a standard or user-defined file in the program and is mostly written at the beginning of any C/C++ program. This directive is read by the preprocessor and orders it to insert the content of a user-defined or system header file into the following program. These files are mainly imported from an outside source into the current program. The process of importing such files that might be system-defined or user-defined is known as File Inclusion. This type of preprocessor directive tells the compiler to include a file in the source code program.
Syntax for #include Directive in C++
#include "user-defined_file"
Including using " ": When using the double quotes(" "), the preprocessor access the current directory in which the source "header_file" is located. This type is mainly used to access any header files of the user's program or user-defined files.
#include <header_file>
Including using <>: While importing file using angular brackets(<>), the the preprocessor uses a predetermined directory path to access the file. It is mainly used to access system header files located in the standard system directories. Header File or Standard files: This is a file which contains C/C++ function declarations and macro definitions to be shared between several source files. Functions like the printf(), scanf(), cout, cin and various other input-output or other standard functions are contained within different header files. So to utilise those functions, the users need to import a few header files which define the required functions. User-defined files: These files resembles the header files, except for the fact that they are written and defined by the user itself. This saves the user from writing a particular function multiple times. Once a user-defined file is written, it can be imported anywhere in the program using the #include preprocessor. • In #include directive, comments are not recognized. So in case of #include <a//b>, a//b is treated as filename. • In #include directive, backslash is considered as normal text not escape sequence. So in case of #include <a\nb>, a\nb is treated as filename. • You can use only comment after filename otherwise it will give error.
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/* using #include directive in C language */ #include <stdio.h> int main() { /* * C standard library printf function * defined in the stdio.h header file */ printf("I love you Clementine"); printf("I love you so much"); printf("HappyCodings"); return 0; }
Classes and Objects in C++ Language
The main purpose of C++ programming is to add object orientation to the C programming language and classes are the central feature of C++ that supports object-oriented programming and are often called user-defined types. A class is used to specify the form of an object and it combines data representation and methods for manipulating that data into one neat package. The data and functions within a class are called members of the class.
C++ Class Definitions
When you define a class, you define a blueprint for a data type. This doesn't actually define any data, but it does define what the class name means, that is, what an object of the class will consist of and what operations can be performed on such an object. A class definition starts with the keyword class followed by the class name; and the class body, enclosed by a pair of curly braces. A class definition must be followed either by a semicolon or a list of declarations. For example, we defined the Box data type using the keyword class as follows:
class Box { public: double length; // Length of a box double breadth; // Breadth of a box double height; // Height of a box };
The keyword public determines the access attributes of the members of the class that follows it. A public member can be accessed from outside the class anywhere within the scope of the class object. You can also specify the members of a class as private or protected which we will discuss in a sub-section.
Define C++ Objects
A class provides the blueprints for objects, so basically an object is created from a class. We declare objects of a class with exactly the same sort of declaration that we declare variables of basic types. Following statements declare two objects of class Box:
Box Box1; // Declare Box1 of type Box Box Box2; // Declare Box2 of type Box
Both of the objects Box1 and Box2 will have their own copy of data members.
Accessing the Data Members
The public data members of objects of a class can be accessed using the direct member access operator (.). It is important to note that private and protected members can not be accessed directly using direct member access operator (.).
Classes and Objects in Detail
There are further interesting concepts related to C++ Classes and Objects which we will discuss in various sub-sections listed below: • Class Member Functions: A member function of a class is a function that has its definition or its prototype within the class definition like any other variable. • Class Access Modifiers: A class member can be defined as public, private or protected. By default members would be assumed as private. • Constructor & Destructor: A class constructor is a special function in a class that is called when a new object of the class is created. A destructor is also a special function which is called when created object is deleted. • Copy Constructor: The copy constructor is a constructor which creates an object by initializing it with an object of the same class, which has been created previously. • Friend Functions: A friend function is permitted full access to private and protected members of a class. • Inline Functions: With an inline function, the compiler tries to expand the code in the body of the function in place of a call to the function. • this Pointer: Every object has a special pointer this which points to the object itself. • Pointer to C++ Classes: A pointer to a class is done exactly the same way a pointer to a structure is. In fact a class is really just a structure with functions in it. • Static Members of a Class: Both data members and function members of a class can be declared as static.
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/* using public and private in C++ Class */ // Program to illustrate the working of // public and private in C++ Class #include <iostream> using namespace std; class Room { private: double length; double breadth; double height; public: // function to initialize private variables void initData(double len, double brth, double hgt) { length = len; breadth = brth; height = hgt; } double calculateArea() { return length * breadth; } double calculateVolume() { return length * breadth * height; } }; int main() { // create object of Room class Room room1; // pass the values of private variables as arguments room1.initData(42.5, 30.8, 19.2); cout << "Area of Room = " << room1.calculateArea() << endl; cout << "Volume of Room = " << room1.calculateVolume() << endl; return 0; }
Constructors in C++ Language
In C++, constructor is a special method which is invoked automatically at the time of object creation. It is used to initialize the data members of new object generally. The constructor in C++ has the same name as class or structure. Constructors are special class functions which performs initialization of every object. The Compiler calls the Constructor whenever an object is created. Constructors initialize values to object members after storage is allocated to the object. Whereas, Destructor on the other hand is used to destroy the class object. • Default Constructor: A constructor which has no argument is known as default constructor. It is invoked at the time of creating object.
Syntax for Default Constructor in C++
class_name(parameter1, parameter2, ...) { // constructor Definition }
• Parameterized Constructor: In C++, a constructor with parameters is known as a parameterized constructor. This is the preferred method to initialize member data. These are the constructors with parameter. Using this Constructor you can provide different values to data members of different objects, by passing the appropriate values as argument.
Syntax for Parameterized Constructor in C++
class class_name { public: class_name(variables) //Parameterized constructor declared. { } };
• Copy Constructors: These are special type of Constructors which takes an object as argument, and is used to copy values of data members of one object into other object.
Syntax for Copy Constructors in C++
classname (const classname &obj) { // body of constructor }
The copy constructor is a constructor which creates an object by initializing it with an object of the same class, which has been created previously. The copy constructor is used to - • Initialize one object from another of the same type. • Copy an object to pass it as an argument to a function. • Copy an object to return it from a function. If a copy constructor is not defined in a class, the compiler itself defines one.If the class has pointer variables and has some dynamic memory allocations, then it is a must to have a copy constructor. The most common form of copy constructor is shown here.
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/* A constructor is a special type of member function that is called automatically when an object is created. In C++, a constructor has the same name as that of the class and it does not have a return type. */ #include <iostream> using namespace std; // declare a class class Wall { private: double length; double height; public: // initialize variables with parameterized constructor Wall(double len, double hgt) { length = len; height = hgt; } // copy constructor with a Wall object as parameter // copies data of the obj parameter Wall(Wall &obj) { length = obj.length; height = obj.height; } double calculateArea() { return length * height; } }; int main() { // create an object of Wall class Wall wall1(10.5, 8.6); // copy contents of wall1 to wall2 Wall wall2 = wall1; // print areas of wall1 and wall2 cout << "Area of Wall 1: " << wall1.calculateArea() << endl; cout << "Area of Wall 2: " << wall2.calculateArea(); return 0; }
Destructors in C++
A destructor is a special member function that works just opposite to constructor, unlike constructors that are used for initializing an object, destructors destroy (or delete) the object. Destructors in C++ are members functions in a class that delete an object. They are called when the class object goes out of scope such as when the function ends, the program ends, a delete variable is called etc. Destructors are different from normal member functions as they don't take any argument and don't return anything. Also, destructors have the same name as their class and their name is preceded by a tilde(~).
Syntax for Destructor in C++
~class_name() { //Some code }
Similar to constructor, the destructor name should exactly match with the class name. A destructor declaration should always begin with the tilde(~) symbol as shown in the syntax above. A destructor is automatically called when: • The program finished execution. • When a scope (the { } parenthesis) containing local variable ends. • When you call the delete operator.
Destructor rules
• Name should begin with tilde sign(~) and must match class name. • There cannot be more than one destructor in a class. • Unlike constructors that can have parameters, destructors do not allow any parameter. • They do not have any return type, just like constructors. • When you do not specify any destructor in a class, compiler generates a default destructor and inserts it into your code.
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/* Destructor is an instance member function which is invoked automatically whenever an object is going to be destroyed. Meaning, a destructor is the last function that is going to be called before an object is destroyed. The thing is to be noted here, if the object is created by using new or the constructor uses new to allocate memory which resides in the heap memory or the free store, the destructor should use delete to free the memory. */ #include <iostream> using namespace std; class HelloWorld{ public: //Constructor HelloWorld(){ cout<<"Constructor is called"<<endl; } //Destructor ~HelloWorld(){ cout<<"Destructor is called"<<endl; } //Member function void display(){ cout<<"Hello World!"<<endl; } }; int main(){ //Object created HelloWorld obj; //Member function called obj.display(); return 0; }
strcpy() Function in C++
Copy string. Copies the C string pointed by source into the array pointed by destination, including the terminating null character (and stopping at that point). To avoid overflows, the size of the array pointed by destination shall be long enough to contain the same C string as source (including the terminating null character), and should not overlap in memory with source. strcpy() is a standard library function in C/C++ and is used to copy one string to another. In C it is present in string.h header file and in C++ it is present in cstring header file. It copies the whole string to the destination string. It replaces the whole string instead of appending it. It won't change the source string.
Syntax for strcpy() Function in C++
#include <cstring> char * strcpy ( char * destination, const char * source );
destination
Pointer to the destination array where the content is to be copied.
source
C string to be copied. destination is returned. After copying the source string to the destination string, the strcpy() function returns a pointer to the destination string. • This function copies the entire string to the destination string. It doesn't append the source string to the destination string. In other words, we can say that it replaces the content of destination string by the content of source string. • It does not affect the source string. The source string remains same after copying. • This function only works with C style strings and not C++ style strings i.e. it only works with strings of type char str[]; and not string s1; which are created using standard string data type available in C++ and not C.
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/* copy a character string from source to destination by strcpy() string function code example */ #include <cstring> #include <iostream> using namespace std; int main() { char src[20] = "I am the source."; // large enough to store content of src char dest[30] = "I am the destination."; cout << "dest[] before copy: " << dest << endl; // copy contents of src to dest strcpy(dest,src); cout << "dest[] after copy: " << dest; return 0; }
main() Function in C++
A program shall contain a global function named main, which is the designated start of the program in hosted environment. main() function is the entry point of any C++ program. It is the point at which execution of program is started. When a C++ program is executed, the execution control goes directly to the main() function. Every C++ program have a main() function.
Syntax for main() Function in C++
void main() { ............ ............ }
void
void is a keyword in C++ language, void means nothing, whenever we use void as a function return type then that function nothing return. here main() function no return any value.
main
main is a name of function which is predefined function in C++ library. In place of void we can also use int return type of main() function, at that time main() return integer type value. 1) It cannot be used anywhere in the program a) in particular, it cannot be called recursively b) its address cannot be taken 2) It cannot be predefined and cannot be overloaded: effectively, the name main in the global namespace is reserved for functions (although it can be used to name classes, namespaces, enumerations, and any entity in a non-global namespace, except that a function called "main" cannot be declared with C language linkage in any namespace). 3) It cannot be defined as deleted or (since C++11) declared with C language linkage, constexpr (since C++11), consteval (since C++20), inline, or static. 4) The body of the main function does not need to contain the return statement: if control reaches the end of main without encountering a return statement, the effect is that of executing return 0;. 5) Execution of the return (or the implicit return upon reaching the end of main) is equivalent to first leaving the function normally (which destroys the objects with automatic storage duration) and then calling std::exit with the same argument as the argument of the return. (std::exit then destroys static objects and terminates the program). 6) (since C++14) The return type of the main function cannot be deduced (auto main() {... is not allowed). 7) (since C++20) The main function cannot be a coroutine.
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/* simple code example by main() function in C++ */ #include <iostream> using namespace std; int main() { int day = 4; switch (day) { case 1: cout << "Monday"; break; case 2: cout << "Tuesday"; break; case 3: cout << "Wednesday"; break; case 4: cout << "Thursday"; break; case 5: cout << "Friday"; break; case 6: cout << "Saturday"; break; case 7: cout << "Sunday"; break; } return 0; }
If Else Statement in C++
In computer programming, we use the if statement to run a block code only when a certain condition is met. An if statement can be followed by an optional else statement, which executes when the boolean expression is false. There are three forms of if...else statements in C++: • if statement, • if...else statement, • if...else if...else statement,
Syntax for If Statement in C++
if (condition) { // body of if statement }
The if statement evaluates the condition inside the parentheses ( ). If the condition evaluates to true, the code inside the body of if is executed. If the condition evaluates to false, the code inside the body of if is skipped.
Syntax for If...Else Statement
if (condition) { // block of code if condition is true } else { // block of code if condition is false }
The if..else statement evaluates the condition inside the parenthesis. If the condition evaluates true, the code inside the body of if is executed, the code inside the body of else is skipped from execution. If the condition evaluates false, the code inside the body of else is executed, the code inside the body of if is skipped from execution. The if...else statement is used to execute a block of code among two alternatives. However, if we need to make a choice between more than two alternatives, we use the if...else if...else statement.
Syntax for If...Else...Else If Statement in C++
if (condition1) { // code block 1 } else if (condition2){ // code block 2 } else { // code block 3 }
• If condition1 evaluates to true, the code block 1 is executed. • If condition1 evaluates to false, then condition2 is evaluated. • If condition2 is true, the code block 2 is executed. • If condition2 is false, the code block 3 is executed. There can be more than one else if statement but only one if and else statements. In C/C++ if-else-if ladder helps user decide from among multiple options. The C/C++ if statements are executed from the top down. As soon as one of the conditions controlling the if is true, the statement associated with that if is executed, and the rest of the C else-if ladder is bypassed. If none of the conditions is true, then the final else statement will be executed.
Syntax for If Else If Ladder in C++
if (condition) statement 1; else if (condition) statement 2; . . else statement;
Working of the if-else-if ladder: 1. Control falls into the if block. 2. The flow jumps to Condition 1. 3. Condition is tested. If Condition yields true, goto Step 4. If Condition yields false, goto Step 5. 4. The present block is executed. Goto Step 7. 5. The flow jumps to Condition 2. If Condition yields true, goto step 4. If Condition yields false, goto Step 6. 6. The flow jumps to Condition 3. If Condition yields true, goto step 4. If Condition yields false, execute else block. Goto Step 7. 7. Exits the if-else-if ladder. • The if else ladder statement in C++ programming language is used to check set of conditions in sequence. • This is useful when we want to selectively executes one code block(out of many) based on certain conditions. • It allows us to check for multiple condition expressions and execute different code blocks for more than two conditions. • A condition expression is tested only when all previous if conditions in if-else ladder is false. • If any of the conditional expression evaluates to true, then it will execute the corresponding code block and exits whole if-else ladder.
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/* If Else Statement in C++ Language */ #include <iostream> using namespace std; int main () { // local variable declaration: int a = 100; // check the boolean condition if( a < 20 ) { // if condition is true then print the following cout << "a is less than 20;" << endl; } else { // if condition is false then print the following cout << "a is not less than 20;" << endl; } cout << "value of a is : " << a << endl; return 0; }
Structures in C++ Language
In C++, classes and structs are blueprints that are used to create the instance of a class. Structs are used for lightweight objects such as Rectangle, color, Point, etc. Unlike class, structs in C++ are value type than reference type. It is useful if you have data that is not intended to be modified after creation of struct. C++ Structure is a collection of different data types. It is similar to the class that holds different types of data.
Syntax for Structures in C++
struct structureName{ member1; member2; member3; . . . memberN; };
A structure is declared by preceding the struct keyword followed by the identifier(structure name). Inside the curly braces, we can declare the member variables of different types. Consider the following situation:
struct Teacher { char name[20]; int id; int age; }
In the above case, Teacher is a structure contains three variables name, id, and age. When the structure is declared, no memory is allocated. When the variable of a structure is created, then the memory is allocated. Let's understand this scenario. Structures in C++ can contain two types of members: • Data Member: These members are normal C++ variables. We can create a structure with variables of different data types in C++. • Member Functions: These members are normal C++ functions. Along with variables, we can also include functions inside a structure declaration. Structure variable can be defined as: Teacher s; Here, s is a structure variable of type Teacher. When the structure variable is created, the memory will be allocated. Teacher structure contains one char variable and two integer variable. Therefore, the memory for one char variable is 1 byte and two ints will be 2*4 = 8. The total memory occupied by the s variable is 9 byte. The variable of the structure can be accessed by simply using the instance of the structure followed by the dot (.) operator and then the field of the structure.
s.id = 4;
We are accessing the id field of the structure Teacher by using the dot(.) operator and assigns the value 4 to the id field. In C++, the struct keyword is optional before in declaration of a variable. In C, it is mandatory.
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/* Structure is a collection of variables of different data types under a single name. It is similar to a class in that, both holds a collecion of data of different data types. */ #include <iostream> using namespace std; struct Person { char name[50]; int age; float salary; }; int main() { Person p1; cout << "Enter Full name: "; cin.get(p1.name, 50); cout << "Enter age: "; cin >> p1.age; cout << "Enter salary: "; cin >> p1.salary; cout << "\nDisplaying Information." << endl; cout << "Name: " << p1.name << endl; cout <<"Age: " << p1.age << endl; cout << "Salary: " << p1.salary; return 0; }
exit() Function in C++
The exit function terminates the program normally. Automatic objects are not destroyed, but static objects are. Then, all functions registered with atexit are called in the opposite order of registration. The code is returned to the operating system. An exit code of 0 or EXIT_SUCCESS means successful completion. If code is EXIT_FAILURE, an indication of program failure is returned to the operating system. Other values of code are implementation-defined.
Syntax for exit() Function in C++
void exit (int status);
status
Status code. If this is 0 or EXIT_SUCCESS, it indicates success. If it is EXIT_FAILURE, it indicates failure. Calls all functions registered with the atexit() function, and destroys C++ objects with static storage duration, all in last-in-first-out (LIFO) order. C++ objects with static storage duration are destroyed in the reverse order of the completion of their constructor. (Automatic objects are not destroyed as a result of calling exit().) Functions registered with atexit() are called in the reverse order of their registration. A function registered with atexit(), before an object obj1 of static storage duration is initialized, will not be called until obj1's destruction has completed. A function registered with atexit(), after an object obj2 of static storage duration is initialized, will be called before obj2's destruction starts. Normal program termination performs the following (in the same order): • Objects associated with the current thread with thread storage duration are destroyed (C++11 only). • Objects with static storage duration are destroyed (C++) and functions registered with atexit are called. • All C streams (open with functions in <cstdio>) are closed (and flushed, if buffered), and all files created with tmpfile are removed. • Control is returned to the host environment. Note that objects with automatic storage are not destroyed by calling exit (C++). If status is zero or EXIT_SUCCESS, a successful termination status is returned to the host environment. If status is EXIT_FAILURE, an unsuccessful termination status is returned to the host environment. Otherwise, the status returned depends on the system and library implementation. Flushes all buffers, and closes all open files. All files opened with tmpfile() are deleted. Returns control to the host environment from the program. exit() returns no values.
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/* terminate the process normally, performing the regular cleanup for terminating programs by exit() function code example */ #include<iostream> using namespace std; int main() { int i; cout<<"Enter a non-zero value: "; //user input cin>>i; if(i) // checks whether the user input is non-zero or not { cout<<"Valid input.\n"; } else { cout<<"ERROR!"; //the program exists if the value is 0 exit(0); } cout<<"The input was : "<<i; }
Standard Library free() Function in C++
Deallocate memory block. A block of memory previously allocated by a call to malloc, calloc or realloc is deallocated, making it available again for further allocations. If ptr does not point to a block of memory allocated with the above functions, it causes undefined behavior. If ptr is a null pointer, the function does nothing. Notice that this function does not change the value of ptr itself, hence it still points to the same (now invalid) location. free() function in C++ <cstdlib> library is used to deallocate a memory block in C++. Whenever we call malloc, calloc or realloc function to allocate a memory block dynamically in C++, compiler allocates a block of size bytes of memory and returns a pointer to the start of the block. The new memory block allocated is not initialized but have intermediate values. free() method is used to free such block of memory. In case the pointer mentioned does not point to any memory block then it may lead to an undefined behavior, but does nothing in case of null pointer. Also after the memory block is made available still the pointer points to the same memory location.
Syntax for free() Function in C++
#include <cstdlib> void free (void* ptr);
ptr
Pointer to a memory block previously allocated with malloc, calloc or realloc. This function does not return any value. • Here ptr refers to a pointer pointing to memory block in C++ that has been previously allocated by malloc, calloc or realloc. Here type of pointer is void because it is capable to hold any type of the pointer and can be cast to any type while dereferencing. • In case pointer mentioned in free function is a null pointer then function does nothing as there is memory block for it to deallocate and returns nothing. • And in case the pointer points to a memory block that has not been allocated using any one of malloc, calloc or realloc method then the behavior of free function can not be predicted. The return type of free() function is void, that means this function returns nothing. All it does is simply deallocating the block of memory pointed by the referred pointer.
How free() Function work in C++?
• Free method is a great tool for dynamic memory management. It is present in <cstdlib> header file. • When a memory block is allocated using std::malloc, std::calloc or std::alloc.a pointer is returned. This pointer is passed to free function, for deallocation. This helps in memory management for the compiler dynamically. • In case the pointer is a null pointer then function does nothing as there is no memory being referenced by the pointer. • As the datatype for the pointer is void then its is capable for dereferencing any type of pointer. • In case the value of the pointer mentioned is not one allocated using these three methods then behavior of free function is undefined. Also it is undefined if the memory block being referenced by the pointer has already been deallocated using std::free or std::realloc method. • This method has no impact on the pointer it just frees the memory block, pointer keep referring to the memory block. • All the dynamic memory allocation and deallocation methods work in synchronize manner so that memory block being referred by the pointer for allocation must be free at that time. Differences in delete and free in C++
delete()
• It is an operator. • It de-allocates the memory dynamically. • It should only be used either for the pointers pointing to the memory allocated using the new operator or for a NULL pointer. • This operator calls the destructor after it destroys the allocated memory. • It is faster.
free()
• It is a library function. • It destroys the memory at the runtime. • It should only be used either for the pointers pointing to the memory allocated using malloc() or for a NULL pointer. • This function only frees the memory from the heap. It does not call the destructor. • It is comparatively slower than delete as it is a function.
Data races
Only the storage referenced by ptr is modified. No other storage locations are accessed by the call. If the function releases a unit of storage that is reused by a call to allocation functions (such as calloc or malloc), the functions are synchronized in such a way that the deallocation happens entirely before the next allocation.
Exceptions
No-throw guarantee: this function never throws exceptions. If ptr does not point to a memory block previously allocated with malloc, calloc or realloc, and is not a null pointer, it causes undefined behavior.
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/* The free() function in C++ deallocates a block of memory previously allocated using calloc, malloc or realloc functions, making it available for further allocations code example. */ #include <iostream> #include <cstdlib> #include <cstring> using namespace std; int main() { char *ptr; ptr = (char*) malloc(10*sizeof(char)); strcpy(ptr,"Hello C++"); cout << "Before reallocating: " << ptr << endl; /* reallocating memory */ ptr = (char*) realloc(ptr,20); strcpy(ptr,"Hello, Welcome to C++"); cout << "After reallocating: " <<ptr << endl; free(ptr); /* prints a garbage value after ptr is free */ cout << endl << "Garbage Value: " << ptr; return 0; }
strlen() Function in C++
Get string length. Returns the length of the C string str. C++ strlen() is an inbuilt function that is used to calculate the length of the string. It is a beneficial method to find the length of the string. The strlen() function is defined under the string.h header file. The strlen() takes a null-terminated byte string str as its argument and returns its length. The length does not include a null character. If there is no null character in the string, the behavior of the function is undefined.
Syntax for strlen() Function in C++
#include <cstring> size_t strlen ( const char * str );
str
a string passed to this function, whose length needs to be found. Here str is the string variable of whose we have to find the length. It takes one parameter which is a pointer that points to the null-terminated byte string. The string is terminated by a null character. If a null character does not terminate it, then the behavior is undefined. It returns an integer giving the length of the passed string. Function returns the length of string. While calculating the total length of a String, the character at the first index is counted as 1 and not 0, i.e. one-based index . The function strlen returns the total number of characters actually present in the char[] and not the total number of character it can hold.
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/* return the length of the C string str by strlen() function code example */ #include <cstring> #include <iostream> using namespace std; int main() { char str1[] = "This a string"; char str2[] = "This is another string"; // find lengths of str1 and str2 // size_t return value converted to int int len1 = strlen(str1); int len2 = strlen(str2); cout << "Length of str1 = " << len1 << endl; cout << "Length of str2 = " << len2 << endl; if (len1 > len2) cout << "str1 is longer than str2"; else if (len1 < len2) cout << "str2 is longer than str1"; else cout << "str1 and str2 are of equal length"; return 0; }
Namespaces in C++ Language
Consider a situation, when we have two persons with the same name, jhon, in the same class. Whenever we need to differentiate them definitely we would have to use some additional information along with their name, like either the area, if they live in different area or their mother's or father's name, etc. Same situation can arise in your C++ applications. For example, you might be writing some code that has a function called xyz() and there is another library available which is also having same function xyz(). Now the compiler has no way of knowing which version of xyz() function you are referring to within your code. A namespace is designed to overcome this difficulty and is used as additional information to differentiate similar functions, classes, variables etc. with the same name available in different libraries. Using namespace, you can define the context in which names are defined. In essence, a namespace defines a scope.
Defining a Namespace
A namespace definition begins with the keyword namespace followed by the namespace name as follows:
namespace namespace_name { // code declarations }
To call the namespace-enabled version of either function or variable, prepend (::) the namespace name as follows:
name::code; // code could be variable or function.
Using Directive
You can also avoid prepending of namespaces with the using namespace directive. This directive tells the compiler that the subsequent code is making use of names in the specified namespace.
Discontiguous Namespaces
A namespace can be defined in several parts and so a namespace is made up of the sum of its separately defined parts. The separate parts of a namespace can be spread over multiple files. So, if one part of the namespace requires a name defined in another file, that name must still be declared. Writing a following namespace definition either defines a new namespace or adds new elements to an existing one:
namespace namespace_name { // code declarations }
Nested Namespaces
Namespaces can be nested where you can define one namespace inside another name space as follows:
namespace namespace_name1 { // code declarations namespace namespace_name2 { // code declarations } }
• Namespace is a feature added in C++ and not present in C. • A namespace is a declarative region that provides a scope to the identifiers (names of the types, function, variables etc) inside it. • Multiple namespace blocks with the same name are allowed. All declarations within those blocks are declared in the named scope. • Namespace declarations appear only at global scope. • Namespace declarations can be nested within another namespace. • Namespace declarations don't have access specifiers. (Public or private) • No need to give semicolon after the closing brace of definition of namespace. • We can split the definition of namespace over several units.
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/* namespaces in C++ language */ // A C++ code to demonstrate that we can define // methods outside namespace. #include <iostream> using namespace std; // Creating a namespace namespace ns { void display(); class happy { public: void display(); }; } // Defining methods of namespace void ns::happy::display() { cout << "ns::happy::display()\n"; } void ns::display() { cout << "ns::display()\n"; } // Driver code int main() { ns::happy obj; ns::display(); obj.display(); return 0; }


In C++ language, Encapsulation is achieved using access specifiers. In encapsulation we make all member variables private, provide public "functions" which allow user to work