Declare large global array

Question

What is the best practice for declaring large, global arrays in C? For example, I want to use myArray throughout the application. However, I lose the use of sizeof() if I do this:

// file.c
char* myArray[] = { "str1", "str2", ... "str100" };

//file.h
extern char* myArray[];


// other_file.c
#include "file.h"
size_t num_elements = sizeof( myArray ); // Can determine size of incomplete type.

Answer 1

You could define the size:

// file.c
char *myArray[100] = { "str1", "str2", ... "str100" };

// file.h
extern char *myArray[100];

Then sizeof should work, but you could also just #define the size or set a variable.

Another options is to count up the length and store it one time in your code...

// file.c
char *myArray[] = { "str1", "str2", ... "strN", (char *) 0 };
int myArraySize = -1;
int getMyArraySize() {
   if( myArraySize < 0 ) {
      for( myArraySize = 0; myArray[myArraySize]; ++myArraySize );
   }
   return myArraySize;
 }


// file.h
extern char *myArray[];
int getMyArraySize();

This would allow an unknown size at compile time. If the size is known at compile time just storing the constant will save the overhead of counting.

Answer 2

I think this is the solution you're looking for:

// file.c
char* myArray[] = { "str1", "str2", ... "str100" };
const size_t sizeof_myArray = sizeof myArray;

//file.h
extern char* myArray[];
extern const size_t sizeof_myArray;