C Struct : typedef Doubt !

Question

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;
}

try to put `typedef struct Record R;` under `struct Record ...` — xhan, Jan 15 '11 at 15:40
@xhan - If I do it, it is a meaningful because symbol `Record` is found earlier. Thanks. — Mahesh, Jan 15 '11 at 15:42
Your code ran fine under GCC (had to change getch to getchar) and VS2005. I suspect your findings are right. — karlphillip, Jan 15 '11 at 15:43
possible duplicate of [What's the syntactically proper way to declare a C struct?](http://stackoverflow.com/questions/4698600/whats-the-syntactically-proper-way-to-declare-a-c-struct) — Jens Gustedt, Jan 15 '11 at 16:10

score 1 · Accepted Answer · answered Jan 15 '11 at 15:44

1

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.

answered Jan 15 '11 at 15:44

Peter Eisentraut

35,221
12
85
90

score 0 · Answer 2 · answered Jan 15 '11 at 16:12

0

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.

answered Jan 15 '11 at 16:12

Giuliano

172
9

smaller is typedef struct { int a; } R; – user411313 Jan 15 '11 at 19:06

score 0 · Answer 3 · answered Jan 15 '11 at 16:30

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;

C Struct : typedef Doubt !

3 Answers3