what is typedef in cpp code example

Example 1: c++ typedef

// typedef [type] [alias]
// Example:
typedef unsigned long int ulong;

ulong someNumber = 158426;

Example 2: TYPEDEF c++

// simple typedef
typedef unsigned long ulong;
 
// the following two objects have the same type
unsigned long l1;
ulong l2;
 
// more complicated typedef
typedef int int_t, *intp_t, (&fp)(int, ulong), arr_t[10];
 
// the following two objects have the same type
int a1[10];
arr_t a2;
 
// common C idiom to avoid having to write "struct S"
typedef struct {int a; int b;} S, *pS;
 
// the following two objects have the same type
pS ps1;
S* ps2;
 
// error: storage-class-specifier cannot appear in a typedef declaration
// typedef static unsigned int uint;
 
// typedef can be used anywhere in the decl-specifier-seq
long unsigned typedef int long ullong;
// more conventionally spelled "typedef unsigned long long int ullong;"
 
// std::add_const, like many other metafunctions, use member typedefs
template< class T>
struct add_const {
    typedef const T type;
};
 
typedef struct Node {
    struct listNode* next; // declares a new (incomplete) struct type named listNode
} listNode; // error: conflicts with the previously declared struct name