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C/CPP: question about a strange way to make a obj array.

So I was browsing around when a some one's screenshot caught my eye.
http://download.freshmeat.net/screenshots/55565.png

You're probably thinking I'm going to refer to the code in the picture, and you're right. Here is the snippet of code I thought was interesting:

Code:

/*...*/

struct error_mark

{

/*...*/

};

struct error_mark error_marks [MAX_MARKS];

/*...*/

The declaration of error_marks is what is new to me. How come the person didn't omit the preceeding 'struct ' and just write it as such?:

Code:

error_mark error_marks [MAX_MARKS];

Thanks in advance.

The declaration

Code:

struct error_mark {

  ...;

};

defines one structure.

The declaration

Code:

struct error_mark error_marks [MAX_MARKS];

defines an array of MAX_MARKS elements called error_marks. Each element of the error_marks array is of the type struct error_mark.

If you try to

Code:

error_mark error_marks [MAX_MARKS];

well, it ain't gonna work; for example:

Code:

#define MAX_MARKS      100



void main (void)

{

        struct  error_mark {

                int    a;

                int    b;

        };



        error_mark error_marks [MAX_MARKS];

}

when you try to compile it

Code:

cc    array.c  -o array

array.c: In function 'main':

array.c:11: error: 'error_mark' undeclared (first use in this function)

array.c:11: error: (Each undeclared identifier is reported only once

array.c:11: error: for each function it appears in.)

array.c:11: error: expected ';' before 'error_marks'

make: *** [array] Error 1

But...

Code:

#define MAX_MARKS      100



int main (void)

{

        struct  error_mark {

                int    a;

                int    b;

        };



        struct  error_mark error_marks [MAX_MARKS];

}

will work just fine.

In the program any element would be referred to simply as

Code:

...

error_marks [1];

error_marks [2];

...

O, I only tried compiling the code in c++ not c. C++(gcc/g++) doesn't throw out errors for the following:

Code:

#include <iostream>



#define MAX 24



struct test1

{

 int a;

};



int main ()

{

 test1 t1s [MAX];



 return 0;

}

/*...*/
struct error_mark
{
/*...*/
};
struct error_mark error_marks [MAX_MARKS];
/*...*/

if you just wanna:

error_mark error_marks [MAX_MARKS];

for that you need to precede the struct..... declaration by "typedef" :

/*...*/
typedef struct error_mark
{
/*...*/
};
error_mark error_marks [MAX_MARKS];
/*...*/

this thing will not give an error now.

But one should avoid using "tpedef".