CODEWITHSUNDEEP
cstructtypedef
Mahesh
Mahesh

Reputation: 34625

C Struct : typedef Doubt !

In the given code snippet, I expected the error symbol Record not found. But it compiled and ran fine on Visual Studio 2010 Compiler. I ran it as a C program from Visual Studio 2010 Command Prompt in the manner -

cl Record.c
Record

Now the doubt is, doesn't typedef check for symbols ? Does it work more like a forward declaration ?

#include "stdio.h"
#include "conio.h"

typedef struct Record R;
struct Record
{
    int a;
};

int main()
{   
    R obj = {10};
    getch();
    return 0;
}

Upvotes: 0

Views: 426

Answers (3)

peoro
peoro

Reputation: 26060

typedef must be used after its first parameter has been defined.

struct Record
{
    int a;
};
typedef struct Record R;

or

typedef struct Record
{
    int a;
} R;

If you need to use struct Record within the struct, just use struct Record:

typedef struct Record
{
    struct Record *next;
}
typedef struct Record R;

Upvotes: 0

Giuliano
Giuliano

Reputation: 192

C does not find the symbol Record because it is declared later on the code, like if you were trying to use a function you declare past on the code without defining its prototype.

You can also combine the two declarations, and then it becomes:

typedef struct Record
{
    int a;
} R;

It also works and, in my opinion, even better, not because it can be faster, but because it is smaller.

Upvotes: 0

Peter Eisentraut
Peter Eisentraut

Reputation: 36729

You can always refer to undefined structures, which is a typical way to implement linked lists, after all. They just have to be defined when you want to make use of their fields. This page contains some details.

Upvotes: 1

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