Solidity Basics II
Learn about predefined global variables, functions, control structures, error handling, events, and function modifiers.
Predefined global variables
A small number of global objects are accessible to a contract during execution in the EVM. These objects are msg
, block
, and tx
. The values of these objects are read-only and cannot be modified within the smart contract.
The msg
object
The msg
object contains several fields that provide information about the current transaction call. Here’s a list of the most commonly used fields:
msg.sender
: The address that initiated the contract call (If the contract is called directly by an EOA transaction, then this is the address of the EOA account, but otherwise, it’s a contract address).msg.value
: The value (in Wei) of Ether sent with the transaction.msg.data
: The data payload for calls to a CA.msg.sig
: It’s the function selector.
The block
object
The block
object contains several fields that provide information about the current block. Here’s a list of the most commonly used fields:
block.number
: The number of the current block.block.timestamp
: The timestamp of the current block, calculated in seconds since the Unix epoch.block.gaslimit
: The maximum amount of gas the current block can contain.block.coinbase
: The address of the miner that mined the current block.
The tx
object
The tx
object contains transaction related information:
tx.gasprice
: The gas price specified by the sender of the transaction.tx.origin
: The original sender of the transaction.
Functions
In Solidity, functions are used to perform specific tasks or operations within a smart contract. Functions can be defined with specific input parameters and may return a value. The syntax to declare a function in Solidity is as follows:
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