How to initialize all members of an array to the same value?

I have a large array in **C** (not **C++** if that makes a difference). I want to initialize all members of the same value.

I could swear I once knew a simple way to do this. I could use `memset()` in my case, but isn't there a way to do this that is built right into the C syntax?

For initializing 'normal' data types (like int arrays), you can use the bracket notation, but it will zero the values after the last if there is still space in the array:

// put values 1-8, then two zeroes
int list[10] = {1,2,3,4,5,6,7,8};

You can do the whole static initializer thing as detailed above, but it can be a real bummer when your array size changes (when your array embiggens, if you don't add the appropriate extra initializers you get garbage).

memset gives you a runtime hit for doing the work, but no code size hit done right is immune to array size changes. I would use this solution in nearly all cases when the array was larger than, say, a few dozen elements.

If it was really important that the array was statically declared, I'd write a program to write the program for me and make it part of the build process.

int i;
for (i = 0; i < ARRAY_SIZE; ++i)
{
myArray[i] = VALUE;
}

I think this is better than

int myArray[10] = { 5, 5, 5, 5, 5, 5, 5, 5, 5, 5...

incase the size of the array changes.

If you want to ensure that every member of the array is explicitly initialized, just omit the dimension from the declaration:

int myArray[] = { 1, 2, 3, 4, 5, 6, 7, 8, 9 };

The compiler will deduce the dimension from the initializer list. Unfortunately, for multidimensional arrays only the outermost dimension may be omitted:

int myPoints[][3] = { { 1, 2, 3 }, { 4, 5, 6 }, { 7, 8, 9} };

is OK, but

int myPoints[][] = { { 1, 2, 3 }, { 4, 5, 6 }, { 7, 8, 9} };

is not.

If the array happens to be int or anything with the size of int or your mem-pattern's size fits exact times into an int (i.e. all zeroes or 0xA5A5A5A5), the best way is to use [memset()][1].

Otherwise call memcpy() in a loop moving the index.


[1]:

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