09 eth smart contract

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Catalog

Preface

Two 、 The code structure of smart contracts

3、 ... and 、 How one contract calls a function in another contract  

Four 、 A special kind of function in smart contract

5、 ... and 、 The creation and operation of smart contracts  

6、 ... and 、 Gas  

7、 ... and 、 Error handling  

8、 ... and 、 Nested calls  

Nine 、 The block information that can be obtained by the contract  

Ten 、 Call information that can be obtained by the contract  

11、 ... and 、 Address type in the contract  

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Preface

    I saw teacher Xiao Zhen of Peking University today 《 Blockchain Technology and application 》 Public class , Have a great harvest , Write a blog here to take notes , Deepen the impression , If there is something wrong , Welcome more .

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One 、 What is a smart contract ？ 

1. A smart contract is a piece of code that runs on a blockchain , The logic of the code defines the contract content  
2. The account of smart contract saves the current running state of the contract

• balance： Current balance
• nonce： Number of transactions
• code： Contract code
• storage： Storage , The data structure is a tree MPT

     3. Solidity Is the most commonly used language for smart contracts , Grammatically with JavaScript Very close to ​​​​​

Two 、 The code structure of smart contracts

This graph shows solidity Code structure of （ because CSDN The picture of cannot be elongated , The picture is not clearly shown , I'm sorry ） 

• The first line states solidity Version number of , Different versions solidity There are some differences in grammar
• solidity Is an object-oriented programming language , there contract Is similar to the Java Medium class
• solidity It's a strongly typed language , The defined state variables are related to C++ These languages are relatively close , In the middle of address The type is solidity Unique in

3、 ... and 、 How one contract calls a function in another contract  

• In the contract B By creating contracts A To call A The function in

•   Using this method can prevent this call from being rolled back when an error occurs in calling other contracts

Four 、 A special kind of function in smart contract

 

• When you need to fallback When the function has the function of accepting transfer , Then add payable keyword  

5、 ... and 、 The creation and operation of smart contracts  

6、 ... and 、 Gas  

• Gasoline is the extra transaction fee you need to pay when you start a transaction , That is to say, you want miners to help you pack your deal , Or you need to pay for executing a smart contract transaction
• Each transaction will be charged for gasoline according to the resources consumed in the execution of the transaction , Every transaction has a gaslimit, That is, the gasoline cost of the transaction set by the initiator , When the transaction is executed, it will be fully deducted gaslimit Gasoline cost of different sizes , Then return the remaining gasoline expenses according to the actual implementation , If the gasoline cost is not enough, it will cause rollback , But the deducted gasoline fee will not be refunded

7、 ... and 、 Error handling  

• Transactions in Ethereum are atomic , A transaction is either fully executed or not executed , There will be no half implementation , This transaction includes both transfer transactions and smart contract transactions , In other words, if a smart contract fails halfway through its execution , It will cause the rollback of the whole transaction  

8、 ... and 、 Nested calls  

• In some cases, on the surface, you don't call functions , For example, you initiate a transfer , But if this collection account is a contract account, it will be different , Your operation may call the contract fallback function  

Nine 、 The block information that can be obtained by the contract  

 

Ten 、 Call information that can be obtained by the contract  

 

11、 ... and 、 Address type in the contract  

 

• The semantics of these member functions are different from our intuitive feelings , for example ：address.banlance() This function is to check the balance in this address , but address.transfer(123456) It means that the contract account transfers money to this address 123456wei

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summary

  Smart contract is a feature of Ethereum and a very important part of Ethereum