Data locations: storage, memory, calldata, stack and transient — Solidity & Smart Contract Development

3. Data locations: storage, memory, calldata, stack and transient

Basic★ Must knowLesson 3 of 11

Location	Lifetime	Cost	Notes
storage	Permanent (contract state)	Most expensive (SSTORE ~20,000 gas for a new non-zero slot, 2,900–5,000 for updates; reads ~2,100 cold / 100 warm)	State variables; storage pointers
memory	During the function call	Cheap, grows quadratically	Temporary arrays/structs, function params of public functions
calldata	Read-only input of external calls	Cheapest for inputs	Use for `external` function array/string params
stack	Local value-type variables	Cheapest	1024 slots max depth; "stack too deep" with too many locals
transient (EIP-1153, Solidity 0.8.28+)	Until end of the transaction	Cheap	Reentrancy locks, temporary approvals

solidity

struct Order { address buyer; uint96 amount; bool paid; }
Order[] public orders;

function markPaid(uint256 id) external {
    Order storage o = orders[id];     // reference to storage → modifies state
    o.paid = true;
}
function preview(uint256 id) external view returns (Order memory) {
    Order memory o = orders[id];      // copy into memory → changes would NOT persist
    return o;
}
function sum(uint256[] calldata xs) external pure returns (uint256 t) {
    for (uint256 i; i < xs.length; ++i) t += xs[i];
}