使用Truffle时遇到的问题和解决方法

问题1

• 错误信息

Error: CompileError: /C/Users/media/ethereum_work/course3/contracts/Ballot.sol:1:1: ParserError: Source file requires different compiler version (current compiler is 0.5.12+commit.7709ece9.Emscripten.clang - note that nightly builds are considered to be strictly less than the released version
pragma solidity ^0.4.17;
^{----------------------}

Error: Truffle is currently using solc 0.5.12, but one or more of your contracts specify “pragma solidity ^0.4.17”.
Please update your truffle config or pragma statement(s).
(See https://truffleframework.com/docs/truffle/reference/configuration#compiler-configuration for information on
configuring Truffle to use a specific solc compiler version.)

Compilation failed. See above.
at Object.compile (C:\Users\media\AppData\Roaming\npm\node_modules\truffle\build\webpack:\packages\workflow-compile\legacy\index.js:80:1)
Truffle v5.1.5 (core: 5.1.5)
Node v12.14.0

• 原因

Truffle和智能合约sol文件的版本不一致导致：sol的版本过低。sol文件的版本在其第一行指定。

• 解决方法：

1. 修改sol文件第一行，pragma solidity ^0.4.17;，提高版本。
2. 或者，修改sol文件的上一级目录下的文件truffle-config.js，改为

// Configure your compilers
  compilers: {
    solc: {
      version: "0.4.17",    // Fetch exact version from solc-bin (default: truffle's version)
    }
  }

问题2

• 错误信息

Error: *** Deployment Failed ***

“Ballot” exceeded the block limit (with a gas value you set).

• Block limit: 0x5fdfb1
• Gas sent: 6721975
• Try:
  • Sending less gas.
  • Setting a higher network block limit if you are on a
    private network or test client (like ganache).

C:\Users\media\AppData\Roaming\npm\node_modules\truffle\build\webpack:\packages\deployer\src\deployment.js:364:1
at processTicksAndRejections (internal/process/task_queues.js:93:5)
at Migration._deploy (C:\Users\media\AppData\Roaming\npm\node_modules\truffle\build\webpack:\packages\migrate\migration.js:70:1)
at Migration._load (C:\Users\media\AppData\Roaming\npm\node_modules\truffle\build\webpack:\packages\migrate\migration.js:57:1)

• 原因
  使用命令truffle migrate --reset部署智能合约的时候设置了过多的gas，大于区块链的限制值。

• 解决方法
  修改truffle_config.js文件的下面部分的gas字段的值，根据自己的错误信息适当减小gas值。

networks: {

    development: {
     host: "127.0.0.1",     // Localhost (default: none)
     port: 8545,            // Standard Ethereum port (default: none)
     network_id: "*",       // Any network (default: none)
     gas: 4700000
    },
  },