из обе пакетов подошвы. Связала соединила вот вид нитью крючком. Петлями из плотных розовой подошвы 20. Петлями. 15-19.
Furthermore we will cover some core concepts Blockchain , Ethereum , A blockchain is an audit-proof digital general ledger of transactions which can record not only financial transactions, but virtually any type of transaction. A blockchain is thus, in the simplest sense, a series of immutable records including time stamps , managed by a decentralized network of computers that do not belong to a single organization or person compared to a central server under the full control of a single organization or person.
These data sets "blocks" are linked by cryptographic principles "chains". A blockchain is therefore a basically simple , but potentially disruptive way of verifying transactions. A party to such a transaction initiates the process by creating a block. This block is checked and confirmed by the computers distributed in the network.
The verified block is then added to the chain , which is stored throughout the network , creating not just a single unique record , but a unique record including a unique history - attempting to forge a single record would mean falsifying the entire chain in potentially millions of cases.
Such a blockchain network is therefore not subject to any central authority - since it is a decentralized and unchangeable general ledger , the information in it i. The cryptocurreny Bitcoin uses this model for payment transactions , but it can also be used in many other ways and is basically potentially suitable for all those applications in which a neutral, timely and audit-proof confirmation of transactions - such as the signing of a contract or the change of ownership of physical or digital goods or rights - is required.
In principle, transactions on such blockchains are free of charge - what usually does incur costs is infrastructure. This is usually covered by the fact that, for example, the initiator of a transaction promises so-called "gas" for those computers in the network that confirm the transaction , as motivation for the operators of those nodes to make their computing power available to the network. Euro depend on the respective exchange rate of ETH.
The more computers in the network confirm the transaction , the more secure in the sense that it took place it can be considered. In comparison to offline processes - for example a notary who confirms a transaction - this results in the potential to significantly reduce costs and time expenditure for such sensitive transactions on the one hand, while on the other hand aspects of audit security and transparency are increased.
A blockchain is an audit-proof decentralized digital general ledger of transactions that can record not only financial transactions, but virtually any type of transaction. The easiest way to describe Ethereum is as an open software platform based on blockchain technology that allows developers to create and deploy distributed applications.
Like Bitcoin , Ethereum is a distributed public blockchain network. Although there are some significant technical differences between the two, the most important difference is that Bitcoin and Ethereum differ significantly in purpose and capability. Bitcoin offers a specialized application of blockchain technology , a peer-to-peer e-payment system that enables online Bitcoin payments.
So while the Bitcoin blockchain is used to track the ownership of the digital currency Bitcoins , the Ethereum blockchain focuses on the execution of program codes of any distributed application. In the Ethereum blockchain , so-called Ether ETH , a crypto token that drives the network, are earned for providing computing power "mining".
In addition to its role as a tradable crypto currency , Ether is also used by application developers to pay transaction fees and services in the Ethereum network. As described at the beginning of this article, the Ethereum blockchain enables the use of tokens which can be bought, sold and traded by users.
These should not be confused with Ether ETH , which is "only" the natural currency of the Ethereum Blockchain infrastructure as described above. Tokens are digital assets or programs based on the blockchain. These tokens serve the purpose of attributing a value to them , such as promissory notes, profit participation rights, services or real objects.
Hence tokens are generally not to be confused with crypto currencies for example Bitcoin or Ether. Tokens are basically so-called "Smart Contracts" , which in the case of ERC20 are executed on the Ethereum block chain. ERC20 is therefore a standard protocol that defines the properties and functionality of an Ethereum blockchain token.
ERC20 is a standard protocol that defines the properties and functionality of an Ethereum blockchain token. A token in general is basically simply a digital representation of potentially anything. For example, a token can represent a stock, a bond, an option, or a property etc.
A token can also represent access rights to a blockchain or blockchain app , and tokens can also be used to automate "friction points" in various industries. Utility tokens , are tokens that have a specific "use" on the blockchain or an app based on that. It contains important data for performing the contract. The field we are using here: msg.
This function will return the number of all tokens allocated by this contract regardless of owner. The transferring owner is msg. In this case that the transferring account has a sufficient balance to execute the transfer.
If a require statement fails, the transaction is immediately rolled back with no changes written into the blockchain. Right before exiting, the function fires ERC20 event Transfer allowing registered listeners to react to its completion. What approve does is to allow an owner i. As you can see, this function is used for scenarios where owners are offering tokens on a marketplace.
It allows the marketplace to finalize the transaction without waiting for prior approval. This function returns the current approved number of tokens by an owner to a specific delegate, as set in the approve function.
The transferFrom function is the peer of the approve function, which we discussed previously. It allows a delegate approved for withdrawal to transfer owner funds to a third-party account. The two require statements at function start are to verify that the transaction is legitimate, i.
This basically allows a delegate with a given allowance to break it into several separate withdrawals, which is typical marketplace behavior. We could stop here and have a valid ERC20 implementation. However, we want to go a step further, as we want an industrial strength token. This requires us to make our code a bit more secure, though we will still be able to keep the token relatively simple, if not basic.
SafeMath is a Solidity library aimed at dealing with one way hackers have been known to break contracts: integer overflow attack. In such an attack, the hacker forces the contract to use incorrect numeric values by passing parameters that will take the relevant integers past their maximal values. SafeMath protects against this by testing for overflow before performing the arithmetic action, thus removing the danger of overflow attack. The library is so small that the impact on contract size is minimal, incurring no performance and little storage cost penalties.
SafeMath uses assert statements to verify the correctness of the passed parameters. Should assert fail, the function execution will be immediately stopped and all blockchain changes shall be rolled back. The name and symbol fields can be changed at will.
Most tokens keep the decimal value at 18, so we will do the same. The time has come to deploy our contract to the blockchain. Following deployment, our contract will be transferred to all nodes participating in the network. Any and all changes made to the contract will be propagated to all participating nodes. Ethereum developers usually employ deployment tools such as Truffle.
Even Truffle is overkill for the limited needs of this article, and a simple online tool called Remix will suffice. To use it, you will need to install the MetaMask plugin on your browser and a Rinkeby Ethereum test network account with at least some Rinkeby Ether in it. Now that we have all the building blocks in place, we will head over to Remix and paste the code above, including the pragma line and the SafeMath library, into the online editor.
You have just deployed your first ERC20 token, like a true Ethereum professional. As promised, the token is simple and lightweight, yet fully functional, ERC20 standard compliant, and secured with MathSafe. It is ready to be purchased, paid with, and transferred throughout the Blockchain. No, not even close, as our brief demonstration barely scratches the surface and deals solely with one aspect of smart contract development. Smart contracts can be much more complex depending on your business logic, your modeling of the user interaction, whether or not you allow token minting and burning, lifecycle changes you introduce into the contract, the need for admin-level capabilities which usually comes with an admin-authorized set of functions, and so on.
You get the picture. Still, if you can replicate what we did here, that is a solid foundation to expand your knowledge and move on to more complex contracts when necessary. A smart contract is a piece of code executed on the Ethereum Virtual Machine. An Ethereum smart contract is immutable and can send or receive ether and data. Operations handled by these contracts include getting the total supply and balance of tokens, and the methods used to transfer them. The number 20 is assigned to this request, hence the suffix.