extern Global array in seperate .h file

Hi,

I'm trying to use a global array declared in a .h file. The array is marked as static and defined in the .cpp file.

I have a macro which gets the size of the array and is defined as such

Code:

#define sizeof_array(x) (sizeof(x)/sizeof(*x))

but when I try to use this function in the code below I get the following error :

Code:

bool contains(string,string[],int);
bool isArithemetic(string first) { return contains(first,cmd_arm,sizeof_array(cmd_arm));

Code:

error C2070: 'std::string []': illegal sizeof operand

This only happens if i declare it as extern, however if I dont, I get a linker error static multiply defined symbols. Here is my header and cpp containing the array -

Code:

//commands.h
#ifdef DEFINE_GLOBALS
#define GLOBAL
#else // !DEFINE_GLOBALS
#define GLOBAL extern
#endif

#define sizeof_array(x) (sizeof(x)/sizeof(*x))

#include <string>
using namespace std;

GLOBAL string cmd_arm[];// = { "+", "-" , "*" ,"/" , "sin", "cos","sqrt" };

Code:

//commands.cpp
#define DEFINE_GLOBALS
#include "Command.h"

string cmd_arm[]  = { "+", "-" , "*" ,"/" , "sin", "cos","sqrt" };

Does anyone know how I can fix this ? or a better way to have a global array ? thanks!

I suppose you might need to specify the size of the array: GLOBAL string cmd_arr[7]. Alternatively I think the array might also be declared static and defined in the header.

Code:

#define sizeof_array(x) (sizeof(x)/sizeof(*x))

I suppose a much better alternative is:

Code:

template <class T, unsigned N>
unsigned sizeof_array(const T (&)[N])
{
     return N;
}

Unlike the macro, this will fail to compile if your array has decayed to a pointer, instead of falsely reporting sizeof(T*) / sizeof(T) - be that 0, 1, 2, 4 or other.