solidity语言4
引用类型（Reference Types）
memory 不支持持久保存
storage 保留为变量
复杂类型如arrays和structs，有附加信息，‘data location’，提示存储在'memory'或者'storage'。函数参数默认使用memory，本地变量默认使用storage.
pragma solidity ^0.4.17;
contract C {
uint[] x; // 存储在storage
function f(uint[] memoryArray) public { // memoryArray存储在memory
x = memoryArray; // 复制memoryArray到storage
var y = x; // y 存储在storage
y[7]; // 返回第8字符
y.length = 2; // 通过y修改x
delete x; // 清除数组，同时修改y
g(x); // 调用g，处理到x的引用
h(x); // 调用h，建立依赖，临时复制到memory
}
function g(uint[] storage storageArray) internal {}
function h(uint[] memoryArray) public {}
}
数组
固定长度数组 T[k]
非固定长度数组 T[]
访问方法 x[2][1]
bytes 和 string是特殊数组，string等同于bytes，但不不允许使用成员属性length和使用索引访问。
成员属性
length
push
在内存中建立数组
使用new关键字在内存中建立可变长度数组，相对于stroge中的数组，它不能使用length改变长度
pragma solidity ^0.4.16;
contract C {
function f(uint len) public pure {
uint[] memory a = new uint[] (7);
bytes memory b = new bytes (len);
// a.length == 7, b.length == len
a[6] = 8;
}
}
数组常量
数组常量只能通过表达式声明，不能批派到变量
pragma solidity ^0.4.16;
contract C {
function f() public pure {
g([uint(1), 2, 3]);
}
function g(uint[3] _data) public pure {
// ...
}
}
以下是错误的
pragma solidity ^0.4.0;
contract C {
function f() public {
// The next line creates a type error because uint[3] memory cannot be converted to uint[] memory.
uint[] x = [uint(1), 3, 4];
}
}
完整例子
pragma solidity ^0.4.16;
contract ArrayContract {
uint[2**20] m_aLotOfIntegers;
// Note that the following is not a pair of dynamic arrays but a
// dynamic array of pairs (i.e. of fixed size arrays of length two).
bool[2][] m_pairsOfFlags;
// newPairs is stored in memory - the default for function arguments
2function setAllFlagPairs(bool[2][] newPairs) public {
// assignment to a storage array replaces the complete array
m_pairsOfFlags = newPairs;
}
function setFlagPair(uint index, bool flagA, bool flagB) public {
// access to a non-existing index will throw an exception
m_pairsOfFlags[index][0] = flagA;
m_pairsOfFlags[index][1] = flagB;
}
function changeFlagArraySize(uint newSize) public {
// if the new size is smaller, removed array elements will be cleared
m_pairsOfFlags.length = newSize;
}
function clear() public {
// these clear the arrays completely
delete m_pairsOfFlags;
delete m_aLotOfIntegers;
// identical effect here
m_pairsOfFlags.length = 0;
}
bytes m_byteData;
function byteArrays(bytes data) public {
// byte arrays ("bytes") are different as they are stored without padding,
// but can be treated identical to "uint8[]"
m_byteData = data;
m_byteData.length += 7;
m_byteData[3] = byte(8);
delete m_byteData[2];
}
function addFlag(bool[2] flag) public returns (uint) {
return m_pairsOfFlags.push(flag);
}
function createMemoryArray(uint size) public pure returns (bytes) {
// Dynamic memory arrays are created using `new`:
uint[2][] memory arrayOfPairs = new uint[2][](size);
// Create a dynamic byte array:
bytes memory b = new bytes(200);
for (uint i = 0; i < b.length; i++)
b[i] = byte(i);
return b;
}
}
posted on
2018-02-27 17:01
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转载于:https://www.cnblogs.com/liujitao79/p/8479824.html
