Summary of typedef usage

Whether it is C or C ++CodeThe word typedef is widely used. Of course, the frequent occurrence is still in the C code. Typedef is similar to # define, but it is more different, especially in some complicated usage, I read some blogs of C/C ++ learners on the Internet. One of the blogs about typedef is still very good. Because of the excellent summary, I will not add any modified references, the following is the reference content (The red part is my own content.).

Purpose 1:

Define a type of Alias, not just a simple macro replacement. It can be used as multiple objects that declare the pointer type at the same time. For example:

Char * pA, PB ;//Most of these do not conform to our intention. It only declares a pointer to a character variable,

//And a character variable;

The following are feasible:

Typedef char * pchar;

Pchar Pa, PB;

This usage is very useful, especially the definition of char * pa and Pb. Beginners often think that two character-type pointers are defined. Actually, this is not the case. Using typedef char * pchar won't happen, reduces errors.

Purpose 2:
It is used in the old C code to help struct. In previous Code, when declaring a new struct objectStruct, in the form of: struct structure name object name, such:

Struct tagpoint1

{
Int X;

Int y;
};

Struct tagpoint1 P1;

In C ++, you can directly write: Structure name object name, that is, tagpoint1 P1;

Typedef struct tagpoint
{
Int X;

Int y;
} Point;

Point P1; // in this way, less struct is written than the original method, which is easier to use, especially when a large number

Mr. Maybe, in C ++, this type of purpose 2 of typedef is not very big, but I understand it and grasp the old generation

Code is still helpful. After all, we may encounter code left over from earlier years in the project.

Purpose 3:

Use typedef to define platform-independent types.

For example, define a floating point type called real. On the target platform 1, make it the highest precision type:

Typedef long double real;

On Platform 2 that does not support long double, change:

Typedef double real;

On Platform 3 that is not supported by double, change:

Typedef float real;

That is to say, when using a cross-platform system, you only need to change the typedef itself, without any modifications to other source codes.

This technique is widely used in the standard library, such as size_t. In addition, because typedef defines a new type of Alias, rather than a simple string replacement, it is more robust than a macro.
This advantage can reduce the amount of Code while writing code!

Purpose 4:

Reprinted from: http://www.cnblogs.com/csyisong/archive/2009/01/09/1372363.html