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Array Members Within Solidity
Example
pragma solidity >=0.4.16 <0.7.0;
contract ArrayContract {
uint[2**20] m_aLotOfIntegers;
// Note that the following is not a pair of dynamic arrays but a
// dynamic array of pairs (i.e. of fixed size arrays of length two).
// Because of that, T[] is always a dynamic array of T, even if T
// itself is an array.
// Data location for all state variables is storage.
bool[2][] m_pairsOfFlags;
// newPairs is stored in memory - the only possibility
// for public contract function arguments
function setAllFlagPairs(bool[2][] memory newPairs) public {
// assignment to a storage array performs a copy of ``newPairs`` and
// replaces the complete array ``m_pairsOfFlags``.
m_pairsOfFlags = newPairs;
}
struct StructType {
uint[] contents;
uint moreInfo;
}
StructType s;
function f(uint[] memory c) public {
// stores a reference to ``s`` in ``g``
StructType storage g = s;
// also changes ``s.moreInfo``.
g.moreInfo = 2;
// assigns a copy because ``g.contents``
// is not a local variable, but a member of
// a local variable.
g.contents = c;
}
function setFlagPair(uint index, bool flagA, bool flagB) public {
// access to a non-existing index will throw an exception
m_pairsOfFlags[index][0] = flagA;
m_pairsOfFlags[index][1] = flagB;
}
function changeFlagArraySize(uint newSize) public {
// if the new size is smaller, removed array elements will be cleared
m_pairsOfFlags.length = newSize;
}
function clear() public {
// these clear the arrays completely
delete m_pairsOfFlags;
delete m_aLotOfIntegers;
// identical effect here
m_pairsOfFlags.length = 0;
}
bytes m_byteData;
function byteArrays(bytes memory data) public {
// byte arrays ("bytes") are different as they are stored without padding,
// but can be treated identical to "uint8[]"
m_byteData = data;
m_byteData.length += 7;
m_byteData[3] = 0x08;
delete m_byteData[2];
}
function addFlag(bool[2] memory flag) public returns (uint) {
return m_pairsOfFlags.push(flag);
}
function createMemoryArray(uint size) public pure returns (bytes memory) {
// Dynamic memory arrays are created using `new`:
uint[2][] memory arrayOfPairs = new uint[2][](size);
// Inline arrays are always statically-sized and if you only
// use literals, you have to provide at least one type.
arrayOfPairs[0] = [uint(1), 2];
// Create a dynamic byte array:
bytes memory b = new bytes(200);
for (uint i = 0; i < b.length; i++)
b[i] = byte(uint8(i));
return b;
}
}