How do I clear/empty a C++ array? Theres array::fill, but looks like its C++11 only? I am using VC++ 2010. How do I empty it (reset to all 0)?
7 Answers
std::fill_n(array, elementCount, 0);Assuming array is a normal array (e.g. int[])
Assuming a C-style array a of size N, with elements of a type implicitly convertible from 0, the following sets all the elements to values constructed from 0.
std::fill(a, a+N, 0);Note that this is not the same as "emptying" or "clearing".
Edit: Following james Kanze's suggestion, in C++11 you could use the more idiomatic alternative
std::fill( std::begin( a ), std::end( a ), 0 );In the absence of C++11, you could roll out your own solution along these lines:
template <typename T, std::size_t N> T* end_(T(&arr)[N]) { return arr + N; }
template <typename T, std::size_t N> T* begin_(T(&arr)[N]) { return arr; }
std::fill( begin_( a ), end_( a ), 0 );std::fill(a.begin(),a.end(),0);for (auto& a : SomeArray) a = 0;
Should you want to populate the array with something other than intrinsic values, std::fill wont cut it; instead I found std::generate useful. e.g. I had a vector of lists I wanted to initialize
std::generate(v.begin(), v.end(), [] () { return std::list<X>(); });You can do ints too e.g.
std::generate(v.begin(), v.end(), [n = 0] () mutable { return n++; });or just
std::generate(v.begin(), v.end(), [] (){ return 0; });but I imagine std::fill is faster for the simplest case
Hey i think The fastest way to handle that kind of operation is to memset() the memory.
Example-
memset(&myPage.pageArray[0][0], 0, sizeof(myPage.pageArray));
A similar C++ way would be to use std::fill
char *begin = myPage.pageArray[0][0];
char *end = begin + sizeof(myPage.pageArray);
std::fill(begin, end, 0);If only to 0 then you can use memset:
int* a = new int[6];
memset(a, 0, 6*sizeof(int));
