The following statements define LENGTH as a synonym for int and then use this typedef to declare length, width, and height as integer variables:
typedef int LENGTH;
LENGTH length, width, height;The following declarations are equivalent to the above declaration:
int length, width, height;Similarly, typedef can be used to define a structure, union, or C++ class. For example:
typedef struct {
int scruples;
int drams;
int grains;
} WEIGHT;The structure WEIGHT can then be used in the following declarations:
WEIGHT chicken, cow, horse, whale;In the following example, the type of yds is "pointer to function with no parameter specified, returning int".
typedef int SCROLL();
extern SCROLL *yds; In the following typedefs, the token struct is part of the type name: the type of ex1 is struct a; the type of ex2 is struct b.
typedef struct a { char x; } ex1, *ptr1;
typedef struct b { char x; } ex2, *ptr2; Type ex1 is compatible with the type struct a and the type of the object pointed to by ptr1. Type ex1 is not compatible with char, ex2, or struct b.
In C++, a typedef name must be different from any class type name declared within the same scope. If the typedef name is the same as a class type name, it can only be so if that typedef is a synonym of the class name. This condition is not the same as in C. The following can be found in standard C headers:
typedef class C { /* data and behavior */ } C;A C++ class defined in a typedef without being named is given a dummy name and the typedef name for linkage. Such a class cannot have constructors or destructors. For example:
typedef class {
Trees();
} Trees;Here the function Trees() is an ordinary member function of a class whose type name is unspecified. In the above example, Trees is an alias for the unnamed class, not the class type name itself, so Trees() cannot be a constructor for that class.