StandardToken¶

Title:	StandardToken
Description:	Zeppelin Solidity Smart Contract that provides a standard ERC-20 compliant token.
Author:	Smart Contract Solutions, Inc.
Solidity Version:	^0.4.18
Relative Path:	`./contracts/supporting/StandardToken.sol`
License:	MIT License
Current Version:	1.4.0
Original Source:	StandardToken Source

1. Imports & Dependencies¶

The following imports and dependencies exist for the StandardToken Smart Contract:

Name	Description
BasicToken	Zeppelin Solidity Smart Contract that implements a Basic form of the ERC-20 standard without allowances, approvals, or transferFrom
ERC20	Zeppelin Solidity Smart Contract that provides the interface required to implement an ERC20 compliant token.

2. Variables¶

There are no variables for the StandardToken Smart Contract.

3. Enums¶

There are no enums for the StandardToken Smart Contract.

4. Events¶

TThere are no events for the StandardToken Smart Contract.

5. Mappings¶

The following mappings exist for the StandardToken Smart Contract:

Name	Mapping Type	Description
allowed	address => mapping( address => uint256)	Mapping to allowance authorisation

6. Modifiers¶

There are no modifiers for the StandardToken Smart Contract.

7. Functions¶

The following functions exist for the StandardToken Smart Contract:

Name	Description
transferFrom	Function transfer tokens from an address to another invoked by an authorised spender address
approve	Function to approve a particular allowance to be transferred by that spender address on the target address
allowance	Function to get the approved allowance for a transfer of tokens from an address by a spender address
increaseApproval	Function to allow increase approved allowance for a spender on a given address
decreaseApproval	Function to allow decrease approved allowance for a spender on a given address

transferFrom¶

Function Name:	transferFrom
Description:	Function transfer tokens from an address to another invoked by an authorised spender address
Function Type:	N/A
Function Visibility:	Public
Function Modifiers:	N/A
Return Type:	bool
Return Details:	returns where the transfer was successful or not

Code¶

The code for the transferFrom function is as follows:

transferFrom 1.4.0 Code¶

function transferFrom(address _from, address _to, uint256 _value) public returns (bool) {
    require(_to != address(0));
    require(_value <= balances[_from]);
    require(_value <= allowed[_from][msg.sender]);

    balances[_from] = balances[_from].sub(_value);
    balances[_to] = balances[_to].add(_value);
    allowed[_from][msg.sender] = allowed[_from][msg.sender].sub(_value);
    Transfer(_from, _to, _value);
    return true;
}

The transferFrom function performs the following:

Checks the _to argument is a valid Ethereum address. If not, it will throw.

Checks that the _value argument is less than or equal to the _from token balance. If not, it will throw

Checks that _value argument is less than or equal to the allowed balance for the msg.sender. If not it will throw.

Removes the _value from the _from token balance. If the balance is insufficient, it will throw

Adds the _value to the _to token balance.

Removes the _value from the allowance for this spender on this address.

Fires the Transfer event

Returns true

Usage¶

The transferFrom function has the following usage syntax and arguments:

	Argument	Type	Details
1	_from	address	Address transfer tokens from
2	_to	address	Address transfer tokens to
3	_value	uint256	Number of tokens to transfer

transferFrom Usage Example¶

transferFrom(0x123456789abcdefghijklmnopqrstuvwxyz98765,
             0x543456789abcdefghijklmnopqrstuvwxyz12234,
             100);

approve¶

Function Name:	approve
Description:	Function to approve a particular allowance to be transferred by that spender address on the target address
Function Type:	N/A
Function Visibility:	Public
Function Modifiers:	N/A
Return Type:	bool
Return Details:	Returns where the approval was successful or not

Code¶

The code for the approve function is as follows:

approve 1.4.0 Code¶

function approve(address _spender, uint256 _value) public returns (bool) {
    allowed[msg.sender][_spender] = _value;
    Approval(msg.sender, _spender, _value);
    return true;
}

The approve function performs the following:

Sets the allowance for the _spender on the msg.sender address to the _value

Fires the Approval event

Returns true

Usage¶

The approve function has the following usage syntax and arguments:

	Argument	Type	Details
1	_spender	address	Address to grant approval to
2	_to	address	Allowance ot grant spender

approve Usage Example¶

 approve(0x123456789abcdefghijklmnopqrstuvwxyz98765,100);

allowance¶

Function Name:	allowance
Description:	Function to approve a particular allowance to be transferred by that spender address on the target address
Function Type:	View
Function Visibility:	Public
Function Modifiers:	N/A
Return Type:	uint256
Return Details:	Returns the Current balance of approved tokens an address can transfer

Code¶

The code for the allowance function is as follows:

allowance 1.4.0 Code¶

function allowance(address _owner, address _spender) public view returns (uint256) {
    return allowed[_owner][_spender];
}

The allowance function performs the following:

Returns true

Usage¶

The allowance function has the following usage syntax and arguments:

	Argument	Type	Details
1	_owner	address	Address subject to allowance
2	_spender	address	Address granted an allowance

allowance Usage Example¶

 allowance(0x123456789abcdefghijklmnopqrstuvwxyz98765,
           0x543456789abcdefghijklmnopqrstuvwxyz12234);

increaseApproval¶

Function Name:	increaseApproval
Description:	Function to increase the existing approved allowance of a spender address on the target address
Function Type:	N/A
Function Visibility:	Public
Function Modifiers:	N/A
Return Type:	bool
Return Details:	Current balance of approved tokens an address can transfer

Code¶

The code for the increaseApproval function is as follows:

increaseApproval 1.4.0 Code¶

function increaseApproval(address _spender, uint _addedValue) public returns (bool) {
    allowed[msg.sender][_spender] = allowed[msg.sender][_spender].add(_addedValue);
    Approval(msg.sender, _spender, allowed[msg.sender][_spender]);
    return true;
}

The increaseApproval function performs the following:

Adds the _addedValue argument to the current allowance

Fires the Approval event

Returns true

Usage¶

The increaseApproval function has the following usage syntax and arguments:

	Argument	Type	Details
1	_spender	address	Address to increase the allowance for
2	_addedValue	address	Amount to add to the allowance

increaseApproval Usage Example¶

 increaseApproval(0x123456789abcdefghijklmnopqrstuvwxyz98765,
                 100);

decreaseApproval¶

Function Name:	decreaseApproval
Description:	Function to increase the existing approved allowance of a spender address on the target address
Function Type:	N/A
Function Visibility:	Public
Function Modifiers:	N/A
Return Type:	bool
Return Details:	Current balance of approved tokens an address can transfer

Code¶

The code for the increaseApproval function is as follows:

decreaseApproval 1.4.0 Code¶

function decreaseApproval(address _spender, uint _subtractedValue) public returns (bool) {
    uint oldValue = allowed[msg.sender][_spender];
    if (_subtractedValue > oldValue) {
        allowed[msg.sender][_spender] = 0;
    } else {
        allowed[msg.sender][_spender] = oldValue.sub(_subtractedValue);
    }
    Approval(msg.sender, _spender, allowed[msg.sender][_spender]);
    return true;
}

The decreaseApproval function performs the following:

Calculates the current approved allowance

If the current value is less than the _subtractedValue argument, the allowance is set to zero

Otherwise it removes the _subtractedValue argument from the allowance

Fires the Approval event

Returns true

Usage¶

The decreaseApproval function has the following usage syntax and arguments:

	Argument	Type	Details
1	_spender	address	Address to decrease the allowance for
2	_subtractedValue	address	Amount to remove from the allowance

decreaseApproval Usage Example¶

 decreaseApproval(0x123456789abcdefghijklmnopqrstuvwxyz98765,
                 100);