CODEWITHSUNDEEP
c++arrays
user1113314
user1113314

Reputation: 839

Why fill() compiles when used on 1 dimensional array, but doesn't on multidimensional one

So can anybody tell me why this code compiles:

int main()
{
    int CCC[1000];
    std::fill(CCC, CCC + 1000, 33);
    return 0;
}

and this doesn't:

int main()
{
    int CCC[1000][4];
    std::fill(CCC, CCC + 1000*4, 33);
    return 0;
}

The compiler gives me the following error:

"incompatible types in assignment of 'const int' to 'int [4]'"

Upvotes: 0

Views: 49

Answers (3)

Sergey Kalinichenko
Sergey Kalinichenko

Reputation: 726609

The compiler is right: the array CCC is composed of four-element arrays int [4], so you cannot assign 33 to them.

If you are on C++11, you can fix this by switching to std::array, creating a temporary array<int,4>, filling it with 33s, and then filling the CCC array with that temporary array, like this:

array<array<int,4>,1000> CCC;
array<int,4> tmp;
std::fill(tmp.begin(), tmp.end(), 33);
std::fill(CCC.begin(), CCC.end(), tmp);

Demo on ideone.

Upvotes: 1

juanchopanza
juanchopanza

Reputation: 227418

You need to pass pointers to the beginning and one past the end of the range, i.e int*:

std::fill(&CCC[0][0], &CCC[0][0] + 1000*4, 33);

Upvotes: 3

niklasfi
niklasfi

Reputation: 15931

What type does CCC have? The correct answer is int ** so a pointer to a pointer pointing to an int.

int[4] is actually a pointer type, so your compiler expects you to pass a pointer to the initialization argument of std::fill. But this is probably not what you want.

Upvotes: 0

Related Questions