mirror of
https://github.com/ethereum/solidity
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126 lines
5.5 KiB
ReStructuredText
126 lines
5.5 KiB
ReStructuredText
**************************************
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Units and Globally Available Variables
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**************************************
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.. index:: wei, finney, szabo, ether
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Ether Units
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===========
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A literal number can take a suffix of `wei`, `finney`, `szabo` or `ether` to convert between the subdenominations of Ether, where Ether currency numbers without a postfix are assumed to be "wei", e.g. `2 ether == 2000 finney` evaluates to `true`.
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.. index:: time, seconds, minutes, hours, days, weeks, years
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Time Units
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==========
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Suffixes of `seconds`, `minutes`, `hours`, `days`, `weeks` and
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`years` after literal numbers can be used to convert between units of time where seconds are the base
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unit and units are considered naively in the following way:
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* `1 == 1 second`
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* `1 minutes == 60 seconds`
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* `1 hours == 60 minutes`
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* `1 days == 24 hours`
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* `1 weeks = 7 days`
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* `1 years = 365 days`
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Take care if you perform calendar calculations using these units, because
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not every year equals 365 days and not even every day has 24 hours
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because of `leap seconds <https://en.wikipedia.org/wiki/Leap_second>`_.
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Due to the fact that leap seconds cannot be predicted, an exact calendar
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library has to be updated by an external oracle.
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These suffixes cannot be applied to variables. If you want to
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interpret some input variable in e.g. days, you can do it in the following way::
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function f(uint start, uint daysAfter) {
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if (now >= start + daysAfter * 1 days) { ... }
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}
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Special Variables and Functions
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===============================
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There are special variables and functions which always exist in the global
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namespace and are mainly used to provide information about the blockchain.
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.. index:: block, coinbase, difficulty, number, block;number, timestamp, block;timestamp, msg, data, gas, sender, value, now, gas price, origin
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Block and Transaction Properties
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------------------------------------
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- `block.coinbase` (`address`): current block miner's address
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- `block.difficulty` (`uint`): current block difficulty
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- `block.gaslimit` (`uint`): current block gaslimit
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- `block.number` (`uint`): current block number
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- `block.blockhash` (`function(uint) returns (bytes32)`): hash of the given block - only for 256 most recent blocks
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- `block.timestamp` (`uint`): current block timestamp
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- `msg.data` (`bytes`): complete calldata
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- `msg.gas` (`uint`): remaining gas
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- `msg.sender` (`address`): sender of the message (current call)
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- `msg.sig` (`bytes4`): first four bytes of the calldata (i.e. function identifier)
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- `msg.value` (`uint`): number of wei sent with the message
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- `now` (`uint`): current block timestamp (alias for `block.timestamp`)
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- `tx.gasprice` (`uint`): gas price of the transaction
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- `tx.origin` (`address`): sender of the transaction (full call chain)
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.. note::
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The values of all members of `msg`, including `msg.sender` and
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`msg.value` can change for every **external** function call.
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This includes calls to library functions.
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If you want to implement access restrictions in library functions using
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`msg.sender`, you have to manually supply the value of
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`sg.sender` as an argument.
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.. note::
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The block hashes are not available for all blocks for scalability reasons.
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You can only access the hashes of the most recent 256 blocks, all other
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values will be zero.
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.. index:: sha3, ripemd160, sha256, ecrecover, addmod, mulmod, cryptography, this, super, selfdestruct, balance, send
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Mathematical and Cryptographic Functions
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----------------------------------------
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`addmod(uint x, uint y, uint k) returns (uint)`:
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compute `(x + y) % k` where the addition is performed with arbitrary precision and does not wrap around at `2**256`.
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`mulmod(uint x, uint y, uint k) returns (uint)`:
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compute `(x * y) % k` where the multiplication is performed with arbitrary precision and does not wrap around at `2**256`.
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`sha3(...) returns (bytes32)`:
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compute the Ethereum-SHA-3 hash of the (tightly packed) arguments
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`sha256(...) returns (bytes32)`:
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compute the SHA-256 hash of the (tightly packed) arguments
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`ripemd160(...) returns (bytes20)`:
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compute RIPEMD-160 hash of the (tightly packed) arguments
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`ecrecover(bytes32, byte, bytes32, bytes32) returns (address)`:
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recover public key from elliptic curve signature - arguments are (data, v, r, s)
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In the above, "tightly packed" means that the arguments are concatenated without padding.
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This means that the following are all identical::
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sha3("ab", "c")
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sha3("abc")
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sha3(0x616263)
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sha3(6382179)
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sha3(97, 98, 99)
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If padding is needed, explicit type conversions can be used: `sha3("\x00\x12")` is the
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same as `sha3(uint16(0x12))`.
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It might be that you run into Out-of-Gas for `sha256`, `ripemd160` or `ecrecover` on a *private blockchain*. The reason for this is that those are implemented as so-called precompiled contracts and these contracts only really exist after they received the first message (although their contract code is hardcoded). Messages to non-existing contracts are more expensive and thus the execution runs into an Out-of-Gas error. A workaround for this problem is to first send e.g. 1 Wei to each of the contracts before you use them in your actual contracts. This is not an issue on the official or test net.
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.. index:: this, selfdestruct
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Contract Related
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----------------
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`this` (current contract's type):
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the current contract, explicitly convertible to `address`
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`selfdestruct(address)`:
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destroy the current contract, sending its funds to the given address
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Furthermore, all functions of the current contract are callable directly including the current function.
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