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?
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];
};
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.
static struct N Node[R][C];then?