Manipulators are helping functions that can modify the input/output (Links to an external site.) stream. It does not mean that we change the value of a variable, it only modifies the I/O stream using insertion (<<) and extraction (>>) operators.

For example, if we want to print the hexadecimal value of 100 then we can print it as:

cout<<setbase(16)<<100

Types of Manipulators

There are various types of manipulators:

1. Manipulators without arguments: The most important manipulators defined by the IOStream library are provided below.
   • endl: It is defined in ostream. It is used to enter a new line and after entering a new line it flushes (i.e. it forces all the output written on the screen or in the file) the output stream.
   • ws: It is defined in istream and is used to ignore the whitespaces in the string sequence.
   • ends: It is also defined in ostream and it inserts a null character into the output stream. It typically works with std::ostrstream, when the associated output buffer needs to be null-terminated to be processed as a C string.
   • flush: It is also defined in ostream and it flushes the output stream, i.e. it forces all the output written on the screen or in the file. Without flush, the output would be the same, but may not appear in real-time.

     Examples:

     
     
     
     

     #include <iostream> #include <istream> #include <sstream> #include <string>    using namespace std;    int main() {     istringstream str("           Programmer");     string line;     // Ignore all the whitespace in string     // str before the first word.     getline(str >> std::ws, line);        // you can also write str>>ws     // After printing the output it will automatically     // write a new line in the output stream.     cout << line << endl;        // without flush, the output will be the same.     cout << "only a test" << flush;        // Use of ends Manipulator     cout << "\na";        // NULL character will be added in the Output     cout << "b" << ends;     cout << "c" << endl;        return 0; }

     Output:

     Programmer
     only a test
     abc
     

2. Manipulators with Arguments: Some of the manipulators are used with the argument like setw (20), setfill (‘*’), and many more. These all are defined in the header file. If we want to use these manipulators then we must include this header file in our program.

   For Example, you can use following manipulators to set minimum width and fill the empty space with any character you want: std::cout << std::setw (6) << std::setfill (’*’);

   • Some important manipulators in <iomanip> are:
     1. setw (val): It is used to set the field width in output operations.
     2. setfill (c): It is used to fill the character ‘c’ on output stream.
     3. setprecision (val): It sets val as the new value for the precision of floating-point values.
     4. setbase(val): It is used to set the numeric base value for numeric values.
     5. setiosflags(flag): It is used to set the format flags specified by parameter mask.
     6. resetiosflags(m): It is used to reset the format flags specified by parameter mask.
   • Some important manipulators in <ios> are:
     1. showpos: It forces to show a positive sign on positive numbers.
     2. noshowpos: It forces not to write a positive sign on positive numbers.
     3. showbase: It indicates the numeric base of numeric values.
     4. uppercase: It forces uppercase letters for numeric values.
     5. nouppercase: It forces lowercase letters for numeric values.
     6. fixed: It uses decimal notation for floating-point values.
     7. scientific: It uses scientific floating-point notation.
     8. hex: Read and write hexadecimal values for integers and it works same as the setbase(16).
     9. dec: Read and write decimal values for integers i.e. setbase(10).
     10. oct: Read and write octal values for integers i.e. setbase(10).
     11. left: It adjusts output to the left.
     12. right: It adjusts output to the right.

   Example:

   #include <iomanip> #include <iostream> using namespace std;    int main() {     double A = 100;     double B = 2001.5251;     double C = 201455.2646;        // We can use setbase(16) here instead of hex        // formatting     cout << hex << left << showbase << nouppercase;        // actual printed part     cout << (long long)A << endl;        // We can use dec here instead of setbase(10)        // formatting     cout << setbase(10) << right << setw(15)          << setfill('_') << showpos          << fixed << setprecision(2);        // actual printed part     cout << B << endl;        // formatting     cout << scientific << uppercase          << noshowpos << setprecision(9);        // actual printed part     cout << C << endl; }

   Output:

   0x64
   _______+2001.53
   2.014552646E+05
   
   

   static_cast in C++ | Type Casting operators

   A Cast operator is an unary operator which forces one data type to be converted into another data type.
   C++ supports four types of casting:

   1. Static Cast
   2. Dynamic Cast
   3. Const Cast (Links to an external site.)
   4. Reinterpret Cast (Links to an external site.)

   Static Cast: This is the simplest type of cast which can be used. It is a compile time cast.It does things like implicit conversions between types (such as int to float, or pointer to void*), and it can also call explicit conversion functions (or implicit ones).
   For e.g.

   #include <iostream> using namespace std; int main() {     float f = 3.5;     int a = f; // this is how you do in C     int b = static_cast<int>(f);     cout << b; }

   Output:

   3

   Now let’s make a few changes in the code.

   
   

   
   

   #include <iostream> using namespace std; int main() {     int a = 10;     char c = 'a';        // pass at compile time, may fail at run time     int* q = (int*)&c;      int* p = static_cast<int*>(&c);     return 0; }

   If you compile the code, you will get an error:

   [Error] invalid static_cast from type 'char*' to type 'int*'

   This means that even if you think you can some how typecast a particular object int another but its illegal, static_cast will not allow you to do this.

   Lets take another example of converting object to and from a class.

   #include <iostream> #include <string> using namespace std; class Int {     int x;    public:     Int(int x_in = 0)         : x{ x_in }     {         cout << "Conversion Ctor called" << endl;     }     operator string()     {         cout << "Conversion Operator" << endl;         return to_string(x);     } }; int main() {     Int obj(3);     string str = obj;     obj = 20;     string str2 = static_cast<string>(obj);     obj = static_cast<Int>(30);     return 0; }

   Run the above code:

   Conversion Ctor called
   Conversion Operator
   Conversion Ctor called
   Conversion Operator
   Conversion Ctor called

   Lets the try to understand the above output:

   1. When obj is created then constructor is called which in our case is also a Conversion Constructor(For C++14 rules are bit changed).
   2. When you create str out of obj, compiler will not thrown an error as we have defined the Conversion operator.
   3. When you make obj=20, you are actually calling the conversion constructor.
   4. When you make str2 out of static_cast, it is quite similar to string str=obj;, but with a tight type checking.
   5. When you write obj=static_cast<Int>(30), you are converting 30 into Int using static_cast.

   Lets take example which involves Inheritance.

   #include <iostream> using namespace std; class Base { }; class Derived : public Base { }; int main() {     Derived d1;     Base* b1 = (Base*)(&d1); // allowed     Base* b2 = static_cast<Base*>(&d1);        return 0; }

   The above code will compile without any error.

   1. We took address of d1 and explicitly casted it into Base and stored it in b1.
   2. We took address of d1 and used static_cast to cast it into Base and stored it in b2.

   As we know static_cast performs a tight type checking, let’s the changed code slightly to see it:

   #include <iostream> using namespace std; class Base { }; class Derived : private Base { // Inherited private/protected not public }; int main() {     Derived d1;     Base* b1 = (Base*)(&d1); // allowed     Base* b2 = static_cast<Base*>(&d1);     return 0; }

   Try to compile the above code, What do you see?? Compilation Error!!!!!!!

   [Error] 'Base' is an inaccessible base of 'Derived'

   The above code will not compile even if you inherit as protected. So to use static_cast, inherit it as public.

   Use static_cast to cast ‘to and from’ void pointer.

   #include <iostream> int main() {     int i = 10;     void* v = static_cast<void*>(&i);     int* ip = static_cast<int*>(v);     return 0; }