How to initialize all members of an array to the same value?
Unless that value is 0 (in which case you can omit some part of the initializerand the corresponding elements will be initialized to 0), there's no easy way.
Don't overlook the obvious solution, though:
int myArray[10] = { 5, 5, 5, 5, 5, 5, 5, 5, 5, 5 };
Elements with missing values will be initialized to 0:
int myArray[10] = { 1, 2 }; // initialize to 1,2,0,0,0...
So this will initialize all elements to 0:
int myArray[10] = { 0 }; // all elements 0
In C++, an empty initialization list will also initialize every element to 0.This is not allowed with C:
int myArray[10] = {}; // all elements 0 in C++
Remember that objects with static storage duration will initialize to 0 if noinitializer is specified:
static int myArray[10]; // all elements 0
And that "0" doesn't necessarily mean "all-bits-zero", so using the above isbetter and more portable than memset(). (Floating point values will beinitialized to +0, pointers to null value, etc.)
If your compiler is GCC you can use following syntax:
int array[1024] = {[0 ... 1023] = 5};
Check out detailed description:http://gcc.gnu.org/onlinedocs/gcc-4.1.2/gcc/Designated-Inits.html
For statically initializing a large array with the same value, without multiple copy-paste, you can use macros:
#define VAL_1X 42#define VAL_2X VAL_1X, VAL_1X#define VAL_4X VAL_2X, VAL_2X#define VAL_8X VAL_4X, VAL_4X#define VAL_16X VAL_8X, VAL_8X#define VAL_32X VAL_16X, VAL_16X#define VAL_64X VAL_32X, VAL_32Xint myArray[53] = { VAL_32X, VAL_16X, VAL_4X, VAL_1X };
If you need to change the value, you have to do the replacement at only one place.
Edit: possible useful extensions
(courtesy of Jonathan Leffler)
You can easily generalize this with:
#define VAL_1(X) X#define VAL_2(X) VAL_1(X), VAL_1(X)/* etc. */
A variant can be created using:
#define STRUCTVAL_1(...) { __VA_ARGS__ }#define STRUCTVAL_2(...) STRUCTVAL_1(__VA_ARGS__), STRUCTVAL_1(__VA_ARGS__)/*etc */
that works with structures or compound arrays.
#define STRUCTVAL_48(...) STRUCTVAL_32(__VA_ARGS__), STRUCTVAL_16(__VA_ARGS__)struct Pair { char key[16]; char val[32]; };struct Pair p_data[] = { STRUCTVAL_48("Key", "Value") };int a_data[][4] = { STRUCTVAL_48(12, 19, 23, 37) };
macro names are negotiable.