# struct defines struct and typedef struct

Source: Internet
Author: User

Divided into three pieces to tell:
1 First://Note different in C and C + +
To define a struct type in C, use a typedef:
typedef struct STUDENT
{
int A;
}stu;
So when declaring a variable, you can: Stu stu1; (if there is no TypeDef, you must use struct Student stu1; declare)
The Stu here is actually the alias of the struct student.stu==struct Student
In addition here can also not write Student (so also cannot struct Student stu1;, must be Stu stu1;)
typedef struct
{
int A;
}stu;
But in C + + It's simple, directly
struct Student
{
int A;
};
Therefore, the structure type student is defined, and the variables are declared directly student stu2.
======================================================================================

2. Second:
If you use typedef in C + +, it will make a difference:
struct Student
{
int A;
}stu1;//STU1 is a variable

typedef struct STUDENT2
{
int A;
}STU2; STU2 is a struct type =struct Student

But the STU2 must first STU2 S2;
Then s2.a=10;
======================================================================================

3 Master the above two, but in the end we'll talk about a problem that doesn't matter much.
If in the C program we write:
typedef struct
{
int num;
int age;
}AAA,BBB,CCC;
What the hell is this?
I personally observe the understanding of the compiler (VC6), which is equivalent to
typedef struct
{
int num;
int age;
}AAA;
typedef AAA BBB;
typedef AAA CCC;
That is to say, AAA,BBB,CCC are all structural types. Any one can be used to declare a variable, as is the case in C + +. But what you should note is that in C + + if the typedef keyword is written out, then AAA,BBB,CCC will be a distinct three object.

Not quite understood here.

The difference between typedef struct and struct:

typedef struct TAGMYSTRUCT
{
int iNum;
Long llength;
} mystruct;

The tagmystruct above is an identifier, and mystruct is the variable type (equal to (Int,char, etc.)).

This statement actually accomplishes two things:

1) Define a new type of structure

struct TAGMYSTRUCT
{
int iNum;
Long llength;
};

Analysis: Tagmystruct is called "tag", that is, "tag", is actually a temporary name, whether or not there is typedefstruct keyword and tagmystruct together, constitute this structure type, this structure exists.

We can use struct tagmystruct varname to define variables, but it is important to note that it is wrong to use tagmystruct varname to define variables, because structs and tagmystruct together can represent a struct type.

2) typedef has a name for this new structure, called MyStruct.

typedef struct TAGMYSTRUCT mystruct;

Therefore, MyStruct is actually equivalent to struct tagmystruct, and we can use MyStruct varname to define variables.

2.

typedef struct TAGMYSTRUCT
{
int iNum;
Long llength;
} mystruct;

In C, there are two ways to apply structural variables after this declaration:

(1) struct TAGMYSTRUCT variable name

(2) MyStruct variable name

In C + +, you can have

(1) struct TAGMYSTRUCT variable name

(2) MyStruct variable name

(3) tagmystruct variable name

struct defines struct and typedef struct

Related Keywords:

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