DaniWeb Forum Index > Software Development > C++

C++ RSS

Creating own datatypes

Please support our C++ advertiser: Intel Parallel Studio Home

•

Join Date: Aug 2004

Posts: 140

Reputation: chound is an unknown quantity at this point

Solved Threads: 1

chound

Offline

Junior Poster

Creating own datatypes

Sep 23rd, 2004

How do we create datatypes in C++. Eg. creating datatype called "myowndatatype" with sizeof(myowndatatype) = 3

•

Join Date: Sep 2004

Posts: 19

Reputation: C#Coder is an unknown quantity at this point

Solved Threads: 0

C#Coder

Offline

Newbie Poster

Re: Creating own datatypes

Sep 23rd, 2004

You can create your own data type by either using a struct or by using a class.

And so you know....

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
//This is invalid
sizeof(myowndatatype) = 3;  //You can't assign a value to a function...
 
//It should be this for seeing how big it is
int size = 0;
size = sizeof(myowndatatype);
//This is invalid
sizeof(myowndatatype) = 3;  //You can't assign a value to a function...

//It should be this for seeing how big it is
int size = 0;
size = sizeof(myowndatatype);

If you need more help on this topic let us know

If you don't know it, learn it ;)

•

Join Date: Sep 2004

Posts: 185

Reputation: Stack Overflow is an unknown quantity at this point

Solved Threads: 4

Stack Overflow Stack Overflow is offline

Offline

C Programmer

Re: Creating own datatypes

Sep 23rd, 2004

Greetings chound,

C provides typedef, a facility for creating new data type names. It makes your name a synonym of the defined data-type:

Help with Code Tags

(Toggle Plain Text)

typedef int Number;

The type Number can be used in declarations and casts in exactly the same ways that the defined type int can be:

Help with Code Tags

C++ Syntax (Toggle Plain Text)

Number i, cars;
Number *blocks[];

Using a synonym for "char *" is similarily declared. Example:

Help with Code Tags

(Toggle Plain Text)

typedef char *Str;

Str s, a[5], *p;

The type being declared in a typedef appears in the position of a variable name, not after the word typedef. The typdef sytax is like the storage classes extern, static, and many others. The typedef declaration does not create a new data-type of any sense. It's simply stated as it adds a new name for some existing type.

typedef is similar to #define, expect that it is interpreted by the compiler. There aren't any new semantics. Variables declared this way have exactly the same properties as variables whose declarations are spelled out explicitly.

Hope this helps,
- Stack Overflow

Following the rules will ensure you get a prompt answer to your question. If posting code, please include BB [code][/code] tags. Your question may have been asked before, try the search facility.

IRC
Channel: irc.daniweb.com
Room: #c, #shell

•

Join Date: Aug 2004

Posts: 140

Reputation: chound is an unknown quantity at this point

Solved Threads: 1

chound

Offline

Junior Poster

Re: Creating own datatypes

Sep 23rd, 2004

by sizeof(myowndatatype) = 3 I meant that the size of the datatype should be 3 bytes

•

Join Date: Sep 2004

Posts: 185

Reputation: Stack Overflow is an unknown quantity at this point

Solved Threads: 4

Stack Overflow Stack Overflow is offline

Offline

C Programmer

Re: Creating own datatypes

Sep 23rd, 2004

C provides a compile-time unary operator called sizeof that can be used to compute the size of any object:

Help with Code Tags

(Toggle Plain Text)

sizeof (type name)

It is impossible to set data to a variable using the sizeof operator, as its only purpose is to tell you the size of your object. Using the following example may help get the size of your object.

Help with Code Tags

(Toggle Plain Text)

typedef int Number;

Number size;

size = sizeof(Number);

Hope this helps,
- Stack Overflow

•

Join Date: Sep 2004

Posts: 19

Reputation: C#Coder is an unknown quantity at this point

Solved Threads: 0

C#Coder

Offline

Newbie Poster

Re: Creating own datatypes

Sep 26th, 2004

•

Originally Posted by chound

by sizeof(myowndatatype) = 3 I meant that the size of the datatype should be 3 bytes

So you want to create a custom data type that has a size of 3 bytes? Why do you want/need a datatype of this specific size?

If we know where you're coming from we might be able to better help you find a solution.

If you don't know it, learn it ;)

•

Join Date: Jun 2004

Posts: 436

Reputation: Chainsaw is an unknown quantity at this point

Solved Threads: 10

Chainsaw

Offline

Unprevaricator

Re: Creating own datatypes

Sep 26th, 2004

This could be 3 bytes:

struct AThreeByteDatatype
{
char s[3];
};

but on Windows the compiler is usually set to an alignment of 2 or 4, meaning that an array of these things will be a multiple of 4 not a multiple of 3.

struct AThreeByteDatatype twoOfThem[2];

sizeof(toOfThem) will likely be 8, not 6.