The C language allows you to define new names for existing types using typedefs. Here is some example code that uses typedefs:

typedef int money; 

int x; 

money y; 

typedef money dollars; 

dollars z; 

x = 10; 

y = x; // OK because x and y are of type int z = y; // OK because y and z are of type int

The first typedef defines money to be a synonym for int. Any declaration that follows this typedef can use money instead of int. The second typedef defines dollars to be a synonym for money, which makes it a synonym for int. Any declaration that follows this typedef can use dollars instead of int.

Typedefs can also be used with struct types:

struct Pair { 

 int x; 

 int y; 

}; 

typedef struct Pair Point;

Point p;

A typedef can occur anywhere that a variable declaration (local or global) can occur. The usual C scoping rules apply to the names in typedefs. Note that typedef int money; is considered to be a declaration of the name money and that both money x; and typedef money dollars; are considered to be uses of the name money.

Cats Grammar:

http://pages.cs.wisc.edu/~loris/cs536s16/asn/p3/files/cats.grammar

Question 2:

Now consider the name-analysis phase of the compiler. Note that, in addition to the usual errors for multiply-defined names and for uses of undefined names, the name analyzer must enforce the following rules:

• The declaration typedef T xxx; is an error if T is not a built-in type (e.g., int, bool) or a struct type (in which case T will be of the form: struct ttt) or a new type defined by a previous typedef in the current or an enclosing scope.

• The declaration typedef T xxx; is an error if xxx has already been declared in the current scope (as a variable, function, parameter, or new type).

• A variable, function, or parameter can only be declared to be of type T if T is either a built-in type or a new type defined by a previous typedef in the current or an enclosing scope. (A variable can still be declared to be of type struct ttt as before.)

Answer each of the following questions:

1. What should be done to process a typedef: typedef T xxx;?

2. What should be done to process the use of a name xxx in a statement?

3. What should be done to process a declaration of a variable, function, or parameter named xxx and declared to be of type T?

4. What information should be stored with each name in the symbol table?

Illustrate your answer by showing the entries that would be in the symbol table after processing the following declarations:

struct MonthDayYear { 

 int month; 

 int day; 

 int year; 

}; 

typedef struct MonthDayYear date; 

date today; 

typedef int dollars; 

dollars salary; 

typedef dollars moreDollars; 

moreDollars md; 

int d;