Error when using static array in a structure C

Question

I want to use a static array inside the following structure:

struct N{
    int id;
    static long history[100];
};
struct N Node[R][C];  // R is # of rows, C is # of coloumns

But I got this error:

P.c:38:2: error: expected specifier-qualifier-list before ‘static’
                 static long history[100];

I don't know why? Does it mean I cannot use static inside structures?

What do you think this keyword does? This is C, not C++, remember. — user4520, Nov 17 '15 at 15:39
*"Does it mean I cannot use static inside structures ?"*. Yes it means exactly that — Manos Nikolaidis, Nov 17 '15 at 15:40
I want to use static because I want to keep the value of the array between function invocations — Mike, Nov 17 '15 at 15:43

score 2 · Accepted Answer · answered Nov 17 '15 at 15:45

Unlike C++ where structs (which are fully equivalent to classes in terms of their functionality) are allowed to have static members, C structs are not allowed to do so.

C allows you to have file-scoped and function-scoped static variables. If history needs to be static, make it static in a function where it is accessed, or in a file if it's accessed by more than one function.

However, if you do need history to be static, your struct becomes functionally equivalent to a single int, because static means "one array shared among all instances of my struct". Good chances are that you needed the array to be non-static, i.e. "each struct has its own history":

struct N{
    int id;
    long history[100];
};

Thank you for your explanation. – Mike Nov 17 '15 at 15:51 — Mike, Nov 17 '15 at 15:51

score 1 · Answer 2 · edited May 23 '17 at 12:23

In C, a struct member cannot be static; you're confusing this with the C++ static for classes (and consequently C++ structs), where it means that a property/method is not intended to be unique to a particular instance of the class (object). Note that in C++ it also means everything it meant in C (and more) - see here for details: The static keyword and its various uses in C++

In C, the static keyword merely specifies the storage class of a symbol - if done locally (in a function), it means roughly that the variable is a global but only visible to that function, and if applied to an actual global variable it restricts its scope to the file where it's declared. For more info, see here: What does "static" mean?

If you "want to keep the value of the array between function invocations", then simply don't write to it in these functions; I suspect your problem is trying to design your program in an object-oriented manner, even though you're using C.

In fact you are right, I want to "simulate" OO manner as C structure since I understand Java well. Thank you for your reply. — Mike, Nov 17 '15 at 15:48

Error when using static array in a structure C

2 Answers2