TRC-20 Contract Interaction

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Interacting with TRC-20 smart contracts on the Tron blockchain is a foundational skill for developers building decentralized applications (dApps), wallets, or token management tools. This guide walks you through calling key TRC-20 contract functions—such as name, symbol, decimals, balanceOf, transfer, approve, transferFrom, and allowance—using multiple methods: HTTP API, TronWeb, and wallet-cli.

All examples use the USDT contract on the Shasta testnet, making it easy to experiment without risking real funds. We’ll focus on both read-only (constant) and state-changing operations, ensuring you understand how to retrieve data and execute transactions securely and efficiently.

Understanding Constant vs. State-Changing Functions

Before diving into code, it's crucial to distinguish between two types of smart contract functions:

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Querying Token Metadata

Get Token Name

Retrieve the full name of the token (e.g., "Tether USD").

HTTP API

POST /wallet/triggerconstantcontract
{
  "contract_address": "419E62BE7F4F103C36507CB2A753418791B1CDC182",
  "function_selector": "name()",
  "owner_address": "41977C20977F412C2A1AA4EF3D49FEE5EC4C31CDFB"
}

TronWeb

const contract = await tronWeb.contract().at("TQQg4EL8o1BSeKJY4MJ8TB8XK7xufxFBvK");
const result = await contract.name().call();
console.log(result); // "Tether USD"

Wallet-cli

TriggerConstantContract TQQg4EL8o1BSeKJY4MJ8TB8XK7xufxFBvK name() # false

Get Token Symbol

Fetch the ticker symbol (e.g., "USDT").

HTTP API

{
  "contract_address": "419E62BE7F4F103C36507CB2A753418791B1CDC182",
  "function_selector": "symbol()",
  "owner_address": "41977C20977F412C2A1AA4EF3D49FEE5EC4C31CDFB"
}

TronWeb

const result = await contract.symbol().call();
console.log(result); // "USDT"

Wallet-cli

TriggerConstantContract TQQg4EL8o1BSeKJY4MJ8TB8XK7xufxFBvK symbol() # false

Get Decimal Precision

Determine the number of decimal places the token supports (usually 6 for USDT).

HTTP API

{
  "contract_address": "419E62BE7F4F103C36507CB2A753418791B1CDC182",
  "function_selector": "decimals()",
  "owner_address": "41977C20977F412C2A1AA4EF3D49FEE5EC4C31CDFB"
}

TronWeb

const result = await contract.decimals().call();
console.log(result); // 6

Wallet-cli

TriggerConstantContract TQQg4EL8o1BSeKJY4MJ8TB8XK7xufxFBvK decimals() # false

Get Total Supply

Check the total number of tokens issued.

HTTP API

{
  "contract_address": "419E62BE7F4F103C36507CB2A753418791B1CDC182",
  "function_selector": "totalSupply()",
  "owner_address": "41977C20977F412C2A1AA4EF3D49FEE5EC4C31CDFB"
}

TronWeb

const result = await contract.totalSupply().call();
console.log(result); // e.g., 100000000000000

Wallet-cli

TriggerConstantContract TQQg4EL8o1BSeKJY4MJ8TB8XK7xufxFBvK totalSupply() # false

Reading and Managing Balances

Check Account Balance

Use balanceOf(address) to get a user’s token balance.

HTTP API

{
  "contract_address": "419E62BE7F4F103C36507CB2A753418791B1CDC182",
  "function_selector": "balanceOf(address)",
  "parameter": "000000000000000000000041977C20977F412C2A1AA4EF3D49FEE5EC4C31CDFB",
  "owner_address": "41977C20977F412C2A1AA4EF3D49FEE5EC4C31CDFB"
}

TronWeb

const address = "TM2TmqauSEiRf16CyFgzHV2BVxBe...";
const result = await contract.balanceOf(address).call();
console.log(tronWeb.fromSun(result)); // Convert from Sun if needed

Wallet-cli

TriggerConstantContract TQQg4EL8o1BSeKJY4MJ8TB8XK7xufxFBvK balanceOf(address) "TM2TmqauSEiRf16CyFgzHV2BVxBejY9iyR" false

Executing Token Transfers

Transfer Tokens

Send tokens from one address to another using transfer(to, amount).

⚠️ Requires transaction fee and broadcasting.

HTTP API

POST /wallet/triggersmartcontract
{
  "contract_address": "419E62BE7F4F103C36507CB2A753418791B1CDC182",
  "function_selector": "transfer(address,uint256)",
  "parameter": "0000000000000000000000...encoded params...",
  "fee_limit": 100000000,
  "call_value": 0,
  "owner_address": "41977C20977F412C2A1AA4EF3D49FEE5EC4C31CDFB"
}

Note: Parameters must be ABI-encoded. Refer to Tron’s official documentation for encoding details.

TronWeb

await contract.transfer("TVDGp...", 1000000).send({
  feeLimit: 1000000
});

Wallet-cli

TriggerContract TQQg4EL8o1BSeKJY4MJ8TB8XK7xufxFBvK transfer(address,uint256) "TBQDyqoJ2ZJHTRDsrGQasyqBm4nUVLbWee",100 false 100000000 0 0 #

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Approve Third-Party Spending

Allow another address to spend tokens on your behalf using approve(spender, amount).

TronWeb

await contract.approve("TA1g2WQiXbU...", 10000000).send({
  feeLimit: 100000000
});

Wallet-cli

TriggerContract TQQg4EL8o1BSeKJY4MJ8TB8XK7xufxFBvK approve(address,uint256) "TBQDyqoJ2ZJHTRDsrGQasyqBm4nUVLbWee",100 false 100000000 0 0 #

Transfer On Behalf of Another (transferFrom)

After approval, a third party can call transferFrom(owner, to, amount).

TronWeb

await contract.transferFrom("TM2TmqauSEiRf...", "TVDGpn...", 100000).send({
  feeLimit: 10_00_0_ });

Wallet-cli

TriggerContract TQQg4EL8o1BSeKJY4MJ8TB8XK7xufxFBvK transferFrom(address,address,uint256) "TApuyuazZnGgxvbNbaGcrUijEFn1oidsAH","TBQDyqoJ2ZJHTRDsrGQasyqBm4nUVLbWee",50 false 100_                                                                

Check Allowance

Query how many tokens one address can spend from another using allowance(owner, spender).

TronWeb

const value = await contract.allowance("TM2TmqauSEiRf...", "TA1g2WQiXbU...").call();
console.log(value);

Wallet-cli

TriggerConstantContract TQQg4EL8o1BSeKJY4MJ8TB8XK7xufxFBvK allowance(address,address) "TApuyuazZnGgxvbNbaGcrUijEFn1oidsAH","TQmDzierQxEFJm1dT5YXnTXqVAfdN9HtXj" false

Transaction Confirmation

After executing a state-changing transaction, verify success using:

getTransactionInfoById <tx_id>

Check the result field:

Core Keywords

Frequently Asked Questions (FAQ)

What is the difference between triggerconstantcontract and triggersmartcontract?

triggerconstantcontract is used for read-only functions like name() or balanceOf() that don’t change blockchain state and don’t cost fees. triggersmartcontract is for write operations like transfer() that modify data and require fees and transaction broadcasting.

Why do I need to encode parameters manually in HTTP API calls?

The Tron network requires ABI-encoded parameters for function inputs. Tools like the Tron Convert Tool help encode addresses and integers into hexadecimal format expected by the smart contract.

Can I test these commands on the mainnet?

Yes, but always test on Shasta or Nile testnets first. Replace the contract address and node URLs accordingly. Never expose private keys in production environments.

How do I handle errors when calling smart contracts?

Always wrap contract calls in try-catch blocks. Common issues include insufficient bandwidth/energy, incorrect parameter encoding, or invalid addresses. Use getTransactionInfoById to debug failed transactions.

Is it safe to use wallet-cli for token transfers?

Wallet-cli is secure if used locally with proper key management. Avoid running it on public or shared systems. For dApps, prefer TronWeb or backend SDKs with secure key storage.

Do I need to pay TRX for every TRC-20 transfer?

Yes. Every state-changing operation consumes bandwidth or energy, which may require freezing TRX or paying in Sun if resources are depleted.

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This guide equips developers with practical knowledge to interact with TRC-20 contracts confidently across different environments. Whether you're querying balances or enabling decentralized exchanges, mastering these patterns is essential for building robust Tron-based applications.