Page 60 - MSDN Magazine, November 2019

Figure 7 Invoking the Smart Contract on the PrivateNet
$ neo-express contract invoke HelloWorld --account testWallet {
"contract-context": < omitted for clarity > "script-hashes": < omitted for clarity > "hash-data": < omitted for clarity > "engine-state": {
"state": 1, "gas-consumed": "1.017", "result-stack": []
} }
{ "txid":
"0x785346a3a338d70dd5bee6a70e1fc807a891d23a8d12d138b6a151b5eeae771e" }
$ neo-express contract storage helloWorld 0x48656c6c6f
key (as string) : Hello
value (as bytes) : 0x576f726c64
(as string) : World constant value : False
The imported contract can now be deployed via the contract deploy command.Youmustspecifyawalletaccounttopaythedeployment GAS price. Invoking a smart contract without specifying a wallet account to pay the invocation GAS cost won’t modify the state of the blockchain. For the HelloWorld contract, this means that nothing will be written to blockchain storage. If you want a contract invo- cation to make durable changes, you can specify a wallet account to pay the GAS cost via the --account argument, as shown in Figure 7.
The HelloWorld contract takes no parameters and returns no values. However, it does modify contract storage in the block- chain. You can dump the storage state for a given contract with the contract storage command. This command lists all the key/value pairs in the blockchain, showing both keys and values as both a hex-encoded byte array and as a UTF-8 encoded string.
Wrapping Up
Smart contracts promise to transform our economic institutions, and the economic relationships and transactions that constitute these institutions. With benefits including standardization, security, reduced latency and transaction certainty and more, the benefits of smart contracts span domains ranging from the securities market, through clinical research and trials, to enterprise supply chains.
In this article we’ve focused on the what, why and how of smart contracts and provided a step-by-step approach to developing, debugging and deploying your first smart contract in C#. n
John deVadoss leads development for NEO Global Development in Seattle. Previously he built Microsoft Digital, .NET Patterns & Practices and .NET Archi­ tecture Strategy. He also incubated Microsoft Azure when he was at Microsoft. Most recently, he launched two machine learning start­ups. deVadoss did his Ph.D. work in machine learning, specializing in recurrent neural networks.
Peng huang is a leading industry blockchain platform strategist. Previously at Microsoft he led the Developer Tools and ISV strategy for Greater China, and product management for .NET Patterns & Practices in Redmond. He’s a senior member of ACM and began his career as an Assembly language coder on the SPARC and x86 platforms.
Thanks to the following technical expert for reviewing this article: Harry Pierson
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