Global functions

 About Global Functions

There are four important global functions we'll cover in this lesson:

Address

Block

Transaction

Message

Global Functions in the Address Context

Any variable of the data type address can use the global functions defined in the address context. The built-in functions defined in the address context are:

Balance: Returns the balance of the address in Wei. For an address mycontract, the function call is defined as 'mycontract.balance;'. This will return the balance of mycontract in Wei. The return type is uint256.

transfer(): Sends the given amount of Wei from the current account to the address mentioned. If you want to send x amount of Wei from the current account to an address mycontract, then the function call will be defined as follows: 'mycontract.transfer(uint256 x);'. The problem with the transfer function is if an error occurs during the transaction, the transaction fails.

send(): Sends the given amount of Wei from the current account to the address mentioned. If you want to send x amount of Wei from the current account to an address mycontract, then the function call will be defined as : 'mycontract.send(uint256 x);'. The return type of the send function is bool, and whenever a transaction encounters an error, the send function returns false. Based on this, appropriate action can be taken. This is what differentiates the send function from the transfer function.

call(), staticcall() and delegatecall(): These low-level functions don't go through the checks by the Solidity compiler. That's why it is not advised not to use them unless absolutely necessary. The call and staticcall functions work in a similar manner as the transfer or send function. However, delegatecall works differently. If A invokes B who makes a delegatecall to C, then the msg.sender in the delegatecall will be A and not B. This way we can preserve the original sender of the message. All these low-level functions take bytes as input and the return type is a combination of bool and bytes data types.

Global Functions in the Block Context

There are several in-built functions that exist in the global namespace, which are used mainly to provide information about the blocks in the blockchain. The global functions defined in the block context are:

block.coinbase: Returns the address of the miner rather than the currently mined block

block.difficulty: Returns the difficulty at the time when the current block was mined

block.timestamp: Returns the timestamp at which the current block was mined

block.gaslimit: Returns the total gaslimit of all the transactions mined in the current block

block.number: Returns the number of the newest block in the blockchain

Global Functions in the Transaction Context

There are functions that exist in the global namespace, which are used mainly to provide information about the transactions in the network. There are two such main functions defined as part of the transaction context. These are:

tx.gasprice: Returns the gas price of the transaction sent by the sender as part of the transaction

tx.origin: Returns the address of the original sender of the transaction

Global Functions in the Message ,ontext

There are some global functions that are used to capture the properties of the messages. The main functions in the Message context are:

msg.value: Returns the number of Wei that was sent with the message or the transaction

msg.sender: Returns the immediate sender of the message or the transaction. Unlike tx.origin, msg.sender returns the address of the previous account in the flow of the message. If A sends the message to B and then B sends it to C, then if C calls msg.sender on that message, it will receive the address of B as the return value.

msg.gasleft: This function returns the remaining gas for the transaction. If an account feels that the gas remaining is inadequate or insufficient for a transaction to complete, then it will fail the transaction.