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Fix Foundry Cast Storage Query Errors

DodaTech Updated 2026-06-26 1 min read

You will learn how to read raw storage data from Ethereum contracts.

The Problem

The foundry cast storage pattern is frequently misapplied in smart contract and dapp development, leading to vulnerabilities, gas inefficiencies, or logic errors. This guide shows the correct implementation and common pitfalls to avoid.

Quick Fix

Wrong

cast storage 0xToken 0  # Raw 32-byte hex

Hex string. No decoding of structs or packed variables.

cast storage 0xToken 0 --decode uint256  # Decodes slot 0 as uint256

Decoded value. Cast handles type conversion.

Prevention

  • Map storage slots using contract source code
  • Use --decode flag with correct types
  • Use keccak256 for mapping slot calculations
  • Use DodaTech's storage slot calculator
  • Verify decoded values against contract state

DodaTech Tools

Built by the developers of Doda Browser, DodaZIP, and Durga Antivirus Pro. Doda Browser's developer tools include a Solidity debugger and transaction inspector. DodaZIP archives secure contract templates for team collaboration. Durga Antivirus Pro scans deployed contracts for known vulnerability signatures.

FAQ

### How do I calculate mapping storage slots?

Mapping slot = keccak256(key . slot). Use cast keccak256 to compute.

Can Cast read struct storage?

Yes. Cast reads raw 32-byte slots. Decode struct fields manually based on layout.

Why is slot 0 value not what I expected?

Variables may be packed in the same slot. Check the contract's storage layout documentation.

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