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Deploying Smart Contracts

When a smart contract is deployed on the blockchain, it can be used by other users or invoked by other contracts. This section describes how to deploy and invoke the smart contract in the Neo blockchain using Neo-CLI or Neo-GUI. The instructions in this section are generic and applicable to all contract types including NEP-5 assets.

What contracts need to be deployed?

When a smart contract needs to store data or to be invoked by another smart contract through syscall System.Contract.Call on the blockchain, it needs to be deployed. Contracts triggered only by the verification trigger, such as the lock contract and multi-signature contract, do not need to be deployed as they will not be invoked by other contracts. Contracts such as return 1+1 do not need to be deployed as they do not require any input parameters.

From the programming language perspective, only when a smart contract will be used as a class library, it needs to be deployed. For example:

  • When a smart contract has variable incoming parameters, it must serve as a storage. The caller or other smart contracts provide the parameters.

  • When a smart contract uses storage it must serve as a class library.

  • When a smart contract implements NEP-5 standard assets, the contract needs to be deployed on the blockchain.

How to deploy?

Smart contracts are deployed by invoking APIs. Usually we use Neo-CLI or Neo-GUI to deploy smart contracts.

Deploying and invoking smart contracts cost fees. For more information, refer to Fees .

Before you start

Make sure you have done the following:

  • Confirmed that your contract should be deployed.

  • Compiled a contract file (*.nef) and a descriptive file of contract (*.manifest.json).

  • Installed Neo-CLI or Neo-GUI and completed block synchronization. For more information, refer to Neo-CLI and Neo-GUI

Deploying contract with Neo-CLI

In Neo-CLI run the following command to deploy your contract:

deploy <nefFilePath> [manifestFile]

  • <nefFilePath> : mandatory. The contract file

  • [manifestFile] : optional. The descriptive file of contract

Example

deploy NEP17.nef

or

deploy NEP17.nef NEP17.manifest.json

After the command is executed, the program deploys the smart contract and pays the fee automatically.

neo> deploy NEP17.nef
Script hash: 0xb7f4d011241ec13db16c0e3484bdd5dd9a536f26
Gas: 10.1477624

Signed and relayed transaction with hash=0xe03aade81fb96c44e115a1cc9cfe984a9df4a283bd10aa0aefa7ebf3e296f757

The contract scripthash

When a contract has been deployed a scripthash is generated as a unified identifier of the contract. The contract scripthash can be converted into the standard 20-byte address for receiving assets from transfer transactions. In that case the contract scripthash is used in big endian format. For example:

  • Contract ScriptHash (big endian): 0xb7f4d011241ec13db16c0e3484bdd5dd9a536f26

  • Corresponding address: NPRCE9me1CdXBA6StQ7kff52p61rHQqnS7

Common errors

Engine faulted

  • Contract already exists

  • .nef is not matched with .manifest

  • either .nef or .manifest is wrong

  • Insufficient fee

Deploying contracts with Neo-GUI

  1. In Neo-GUI click Contract -> Deploy Contract

  2. Select the desired *.nef and *.manifest.json files.

  3. Click Deploy .