How to Fix "Stack Too Deep" Error?

Question

I know that this has been covered in other questions here but I'm not sure what's happening in my case. My code is returning a compiler error "Stack too deep, try removing local variables." But I only have around five function arguments and a few more local variables. The function in question is given below:

function sell(bool limit, uint256 whichquery, uint8 whichoutcome, uint256 amount, uint16 price) {
        uint cumulativeamountgained;
        uint numorderstobedeleted;
        uint amountnotfilled = amount;
        if(tokenHoldings[msg.sender][whichquery][whichoutcome] < amount) throw;
        if(limit){
            for (uint i=orderbook[whichquery][whichoutcome][0].length-1;i>=0;i--){
                if(orderbook[whichquery][whichoutcome][0][i][0] >= price) {
                    if(orderbook[whichquery][whichoutcome][0][i][1] > amountnotfilled){
                        orderbook[whichquery][whichoutcome][0][i][1] -= amountnotfilled;
                        tokenHoldings[address(orderbook[whichquery][whichoutcome][0][i][2])][whichquery][whichoutcome] += amountnotfilled;

The error is triggered on the last line of this code snippet under the first "whichquery".

Markus - soliditydeveloper.com · Answer

You can also scope variables like this
uint var1;
{
    (uint varA, uint varB) = getVars();
    var1 = varA + varB;
}

// now use var1

Inspired by Uniswap.

k06a · Answer

Found nice trick to avoid "Stack too deep" issue:

function swapWithReferral(
    IERC20 fromToken,
    IERC20 destToken,
    uint256 amount,
    uint256 minReturn,
    uint256[] calldata distribution,
    uint256 flags,
    address referral,
    uint256 feePercent
) external makeGasDiscount(flags) returns(uint256 returnAmount) {
    ...
    fromToken.transferFrom(address(this), amount); // <-- Stack too deep
    ...
    destToken.transfer(msg.sender, returnAmount);  // <-- Stack too deep
    ...
}

Just define few additional internal functions like _fromToken() and _destToken() to decode args:

// Helps to avoid "Stack too deep" in swap() method
function _fromToken(bytes memory data) internal pure returns(IERC20 token) {
    assembly {
        token := mload(add(data, 36))
    }
}

// Helps to avoid "Stack too deep" in swap() method
function _destToken(bytes memory data) internal pure returns(IERC20 token) {
    assembly {
        token := mload(add(data, 68))
    }
}

And use these functions instead of access to those vars:

function swapWithReferral(
    IERC20 /*fromToken*/,
    IERC20 /*destToken*/,
    uint256 amount,
    uint256 minReturn,
    uint256[] calldata distribution,
    uint256 flags,
    address referral,
    uint256 feePercent
) external makeGasDiscount(flags) returns(uint256 returnAmount) {
    ...
    _fromToken(msg.sender).transferFrom(address(this), amount); // Works great!
    ...
    _destToken(msg.sender).transfer(msg.sender, returnAmount);  // Works great!
    ...
}

Notice: Be careful with internal and public functions, since msg.data is updated only on external calls. You can externally call public function with this.doSomething().

Sanchit · Answer

The limit of having not more than 16 local variables could be a problem here. You can try to refactor your code and probably break this function into two parts. That should fix the issue I hope.

Please read the article Solidity stack too deep by James Carlyle to understand more about this issue.

coderwithattitude · Answer

there is limited amount of local variables you are allowed to declare in your function(arguments and return types inclusive), i think it is 16, but as it seems you have exceeded that limit.

How to Fix "Stack Too Deep" Error?

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