c++ - What does constructor do in this line? -

-

there simple code, found in c++ tutorial. can't understand line:

c1 = complex(10.0);

in comments written constructor can used convert 1 type another. can explain moment. thank help.

#include <iostream> using namespace std;  class complex {   public:     complex() : dreal(0.0), dimag(0.0)     { cout << "invoke default constructor" << endl;}     /*explicit*/ complex(double _dreal)       : dreal(_dreal), dimag(0.0)     { cout << "invoke real constructor " << dreal <<endl;}     complex(double _dreal, double _dimag)       : dreal(_dreal), dimag(_dimag)     {         cout << "invoke complex constructor " << dreal              << ", " << dimag << endl;     }      double dreal;     double dimag; };  int main(int argcs, char* pargs[]) {     complex c1, c2(1.0), c3(1.0, 1.0);      // constructor can used convert 1 type     //     c1 = complex(10.0);      // following conversions work if explicit     // uncommented     c1 = (complex)20.0;     c1 = static_cast<complex>(30.0);      // following implicit conversions work if     // explicit commented out     c1 = 40.0;     c1 = 50;      system("pause");     return 0; }

this right here:

complex(double _dreal)       : dreal(_dreal), dimag(0.0)     { cout << "invoke real constructor " << dreal <<endl;}

is constructor take double , create complex object it. can see set real part (dreal) value passed constructor (_dreal), , setup imaginary part 0.

this line:

c1 = complex(10.0);

will call constructor, , convert passed real number (10.0) complex object.

edit: please note not real conversion - explicitly creation of complex object passing double - have examples of conversions in answer provided dasblinkedlight.


Comments

Post a Comment

Popular posts from this blog

c# - How Configure Devart dotConnect for SQLite Code First? -

-
can configure following sample code ? when run following code, error : no entity framework provider found ado.net provider invariant name 'devart.data.sqlite' setting in machine.config <system.data> <dbproviderfactories> <add name="dotconnect sqlite" invariant="devart.data.sqlite" description="devart dotconnect sqlite" type="devart.data.sqlite.sqliteproviderfactory, devart.data.sqlite, version=4.6.287.0, culture=neutral, publickeytoken=09af7300eec23701" /> </dbproviderfactories> </system.data> after add below block code in app.config <?xml version="1.0"?> <configuration>   <configsections> <!-- more information on entity framework configuration, visit http://go.microsoft.com/fwlink/?linkid=237468 --> <section name="entityframework" type="system.data.entity.internal.configfile.entityframeworksection, entit...
Read more

java - Copying object fields -

-
what best way of copying classes when need have 2 independent variables? have simple class: public class myclass { boolean = false; string b= "not empty"; } do need make method : assign(myclass data ) { a= data.a; b= data.b; } is there automatic method copy (duplicate) objects in java? do need make method : pretty close. instead of making method, should make constructor. such constructors called copy constructor , , create them this: myclass(myclass data) { = data.a; b = data.b; } and create copy of instance, use constructor this: myclass obj1 = new myclass(); myclass obj2 = new myclass(obj1); copy constructor can tedious : using copy constructor create deep-copy can tedious, when class has mutable fields. in case, assignment create copy of reference, , not object itself. have create copy of fields (if want deep copy). can go recursive. a better way create deep copy serialize , deserialize object. why not use clone()? ...
Read more

c++ - Clear the memory after returning a vector in a function -

-
i have function processes , stores lot of data in , returns results vector of class. amount of data stored in function tremendous , want clear storage memory of function after finished job. necessary (does function automatically clear memory) or should clear memory function? update: vector<customers> process(char* const *filename, vector<int> id) { vector<customers> list_of_customers; (perform actions) return list_of_customers; } variables defined locally within function automatically released @ end of function scope. destructors objects called, should free memory allocated objects (if objects coded correctly). example of such object std::vector . anything you've allocated new must have corresponding delete release storage. try avoid doing own allocation , use raii instead, i.e. containers or smart pointers.
Read more