Understanding Smart Contract Functions
Published: August 15, 2025 | Reading time: 10 minutes
Smart contracts can seem intimidating to newcomers, but understanding their basic functions is crucial for safely navigating DeFi. This guide will help you read and understand common smart contract functions you'll encounter.
Read vs Write Functions
Smart contract functions are divided into two categories:
- Read Functions: Query information without changing the blockchain state (free to call)
- Write Functions: Modify the blockchain state and require gas fees
Common Read Functions
balanceOf(address)
Returns the token balance of a specific address. Essential for checking how many tokens you hold in a contract.
totalSupply()
Shows the total number of tokens in circulation. Useful for understanding token economics.
allowance(owner, spender)
Checks how many tokens the owner has approved the spender to use on their behalf.
getReserves()
In liquidity pools, this shows the current reserves of each token in the pair.
Common Write Functions
approve(spender, amount)
Gives permission to another address (usually a contract) to spend your tokens. Always check the amount carefully!
transfer(to, amount)
Sends tokens from your address to another address.
deposit(amount) / stake(amount)
Deposits tokens into a protocol, usually for earning rewards.
withdraw(amount) / unstake(amount)
Removes your tokens from a protocol.
emergencyWithdraw()
A failsafe function that withdraws your principal without claiming rewards. Often used when protocols have issues.
Reading Function Parameters
Functions often require parameters (inputs). Common parameter types include:
- address: A wallet or contract address (42 characters starting with 0x)
- uint256: A large number, often representing token amounts
- bool: True or false value
- bytes: Raw data, often used for complex operations
Understanding Token Amounts
Token amounts in smart contracts use "wei" units. For most tokens:
- 1 token = 1,000,000,000,000,000,000 wei (18 decimal places)
- To withdraw 100 tokens, you'd enter: 100000000000000000000
- Use online converters or calculators to avoid mistakes
Safety Tips
- Always double-check function names and parameters
- Start with small amounts when testing
- Verify the contract address is correct
- Understand what each function does before calling it
- Check gas estimates - unusually high gas might indicate an error
When to Get Help
If you're unsure about any function or see unfamiliar parameters, don't guess. The cost of professional help is usually much less than the potential loss from a mistake.
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