CODEWITHSUNDEEP
cdata-structuresstructtypedef
user3340866
user3340866

Reputation: 53

Difference between structure instance and name

What is the difference between

typedef struct complex {
    int x;
    int y;
};

and

typedef struct complex { 
    int x;
    int y;
} comp;

What does the additional comp in the second case do? I have tried defining a new variable of type complex in the first case and using comp in the second case, both produced the same result... Please help!

Upvotes: 4

Views: 1082

Answers (4)

Logar
Logar

Reputation: 1248

Long story short :

struct complex {
    int x;
    int y;
};
// forces you to use :
struct complex c;

But :

typedef struct complex {
    int x;
    int y;
} comp;
// allows you to use :
comp c;

Typedefs are just a matter of readabilty

Upvotes: 0

OldSchool
OldSchool

Reputation: 2183

struct complex {
    int x;
    int y;
} comp;

This is the shorthand of creating variable of type complex. comp is present before ; so it is treated as variable of type complex.look ar following code also

struct {
    int x;
    int y;
} comp;

You can also do this with old compilers that creates a variable of its struct type.

Upvotes: 0

mtrudeau
mtrudeau

Reputation: 9

The purpose of typedef is to assign a simple name to a type declaration made of one or more type components.

In the first declaration, you do not assign any name to your structure named complex. Therefore the compiler will be generating a warning:

i.e. warning: declaration does not declare anything

Usually, when using typedef with structures [ or unions ], it is preferable (less verbose) to use unnamed structures, as in:

typedef struct {int x; int y;} complex;

Upvotes: 1

Yu Hao
Yu Hao

Reputation: 122463

The first typedef is useless, the compile may give you a warning for it.

After the second typedef, whenever you use struct complex as a type, you can use comp instead. You can modify the second code into this equivalent form:

struct complex { 
    int x;
    int y;
};
typedef struct complex comp;

You can see that struct complex defines a type, while typedef gives it an alternative name.

Upvotes: 4

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