What is the difference between typedef and DEF?

1) #define是预处理指令, will not participate in the compilation process, only in the compilation of pre-processing simple replacement, do not check for correctness, whether the meaning is correct or not, only when compiling the source program has been expanded to find possible errors and error. For example:
#define PI 3.1415926
In the program: Area=pi*r*r will be replaced with 3.1415926*r*r
If you write the number 9 in the # define statement as the letter G preprocessing is also brought in.

2) A typedef is processed at compile time. It gives an alias to an already existing type within its scope, but you cannot use the typedef specifier inside a function definition.

3) typedef int * INT_PTR; With # define INT_PTR int *
The function is to use INT_PTR to represent the int *, but the two are different, as mentioned earlier, a simple substitution #define在预处理, whereas a typedef is not a simple substitution, but rather a type declared as a method of defining a variable. That is

#define int_ptr int *//相当于int * a, b; 只是简单的宏替换int//a, b 都为指向int的指针,typedef为int* 引入了一个新的助记符

This also explains why the following ideas are set up

typedef int * PINT;
#define PINT int *

So:
Const pint p;//p cannot be changed, but P points can be changed
The const PINT p;//p can be changed, but the content that P points to cannot be changed.

Pint is a pointer-type const pint p is a pointer to the lock p cannot be changed
The const PINT p is a const int * p Lock that is the object referred to by the pointer p.

4) Perhaps you have noticed that # define is not a statement do not add a semicolon at the end of the line, or a semicolon is replaced.

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What is the difference between typedef and DEF?