CODEWITHSUNDEEP
cdata-structuresstructtypedefcs50
herbNotz
herbNotz

Reputation: 21

How does the compiler differentiate typedef struct implementation with the type having the same name as the structure?

I've been studying singly linked lists and crossed with two different typedef struct implementations.

1st (at CS50 lecture explanation):

// Represents a node:

typedef struct node
{
    int number;
    struct node *next;
}
node;

2nd (at CS50 short videos explanation):

typedef struct sllist
{
    int number;
    struct sllist *next;
}
sllnode;

My question is: In the former implementation, how is the compiler able to differentiate between node, the alias and node, the struct? Why is it able to differentiate struct from typedef, but I cannot use the same variable name for representing int and string, for example?

Upvotes: 1

Views: 139

Answers (1)

Marco Bonelli
Marco Bonelli

Reputation: 69367

how is the compiler able to differentiate between node, the alias and node, the struct?

Pretty easy: they are two different things. One is preceded by the struct keyword, one is not. The typedef can be seen as creating an alias. If the compiler sees node alone, it looks at the typedef to get the real type, while if it sees struct node it already knows the type.

Why is it able to differentiate struct from typedef, but I cannot use the same variable name for representing int and string, for example?

That's a different scenario. You cannot re-define a type name that already exists. You cannot do typedef something int; because int already exists, the same way as you cannot do:

struct s {
    int a;
};

struct s {
    int a;
};

This single definition rule also applies to variable names and function names.

Upvotes: 2

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