C ++ struct, union and enum

Struct

StructYesIGroupData ElementA name,These data elements,As a member,YesDifferent Types and differencesLength. C ++ statement structSyntax::

Struct structure_name {
Member_type1 member_name1;
Member_type2 member_name2;
Member_type3 member_name3;
.
.
} Object_names;

A simple example is as follows:

 
StructProduct {
IntWeight;
FloatPrice;
};

Product apple;
Product banana, melon;
 

Declare struct and define multiple instances:

StructProduct {
IntWeight;
FloatPrice;
} Apple, banana, melon;
 

Complete struct example:

 //  Example about structures  
 # Include <iostream>
# Include < String >
# Include <sstream>
 Using   Namespace STD;

 Struct Movies_t {
 String Title;
 Int Year;
} Mine, yours;

 Void Printmovie (movies_t movie );

 Int Main ()
{
 String Mystr;

Mine. Title = "  2001 A Space Odyssey  " ;
Mine. Year = 1968 ;

Cout <"  Enter title:  " ;
Getline (CIN, yours. Title );
Cout < "  Enter year:  " ;
Getline (CIN, mystr );
Stringstream (mystr)> yours. Year;

Cout < "  My favorite movie is: \ n  " ;
Printmovie (mine );
Cout <"  And yours is: \ n  " ;
Printmovie (yours );
 Return   0 ;
}

 Void Printmovie (movies_t movie)
{
Cout <movie. title;
Cout < "  (  " <Movie. year < " ) \ N  " ;
}

  Struct and pointer

 
StructMovies_t {
StringTitle;
IntYear;
};

Movies_t amovie;
Movies_t * pmovie;
Pmovie = & amovie;
 

Complete example:

 //  Pointers to structures  
 # Include <iostream>
# Include < String >
# Include <sstream>
Using   Namespace STD;

 Struct Movies_t {
 String Title;
 Int Year;
};

 Int Main ()
{
 String Mystr;

Movies_t amovie;
Movies_t * pmovie;
Pmovie = & amovie;

Cout <"  Enter title:  " ;
Getline (CIN, pmovie-> title );
Cout < "  Enter year:  " ;
Getline (CIN, mystr );
(Stringstream) mystr> pmovie-> year;

Cout < "  \ Nyou have entered: \ n  " ;
Cout <pmovie-> title;
Cout <"  (  " <Pmovie-> year < "  ) \ N  " ;

 Return   0 ;
}

  Internal struct

StructMovies_t {
StringTitle;
IntYear;
};

StructFriends_t {
StringName;
StringEmail;
Movies_t favorite_movie;
} Charlie, Maria;

Friends_t * pfriends = & Charlie;
 

Use:

 
Charlie. Name
Maria. favorite_movie.title
Charlie. favorite_movie.year
Pfriends-> favorite_movie.year
 

Union

UnionAllowDifferent Data TypesSame memory,Because theyActuallyIn MemoryOfSameLocation, which is similar to struct, but has different functions:

Union union_name {
Member_type1 member_name1;
Member_type2 member_name2;
Member_type3 member_name3;
.
.
} Object_names;
 

Union statementOfAllElementIn MemoryMediumPossessionSame physical space,Its size isStatementOfMaxElement size:

 
Union mytypes_t {
CharC;
IntI;
FloatF;
} Mytypes;
 

 

EachOneDifferent Data Types.BecauseAll elements areIndicates thatSame in memoryLocation,ModifyOne,Will affectOther elements.

  Anonymous Union

Struct and normal Union

 
Struct{
CharTitle [50];
CharAuthor [50];
Union {
FloatDollars;
IntYen;
} Price;
} Book;
 

Struct and anonymous Union

 
Struct{
CharTitle [50];
CharAuthor [50];
Union {
FloatDollars;
IntYen;
};
} Book;
 

The first type of access method is as follows:

 
Book. Price. dollars
Book. Price. Yen
 

The second type of access method is as follows:

 
Book. dollars
Book. Yen
 

 

Enum

Basic syntax for defining enumeration types:

 
Enum enumeration_name {value1, value2, value3,...} object_names;
 

For example:

 
EnumWeek {Sunday, Monday, Tuesday, Wednesday, Thursday, Friday, Saturday };
 

Sunday = 0, Monday = 1 ...... Saturday = 6. That is to say, 1st enumerated values represent 0, and 2nd enumerated values represent 1, which increases by 1 in turn.

You can also specify the values of one or more enumerated values when defining them. For example:

 
 EnumWeek {Monday =1, Tuesday, Wednesday, Thursday, Friday, Saturday, Sunday };
 

Monday is equal to 1, so that Tuesday is equal to 2 and Sunday is equal to 7.

 

Declare enumerated variables:

 
Week today = Tuesday;
 

 

The enumerated value is called a lattice constant, because it cannot be changed once defined. The following usage is incorrect!

 
Tuesday =10;//Error! We cannot change the value of an enumerated value.