solidity整型溢出举例分析

这篇文章主要讲解了"solidity整型溢出举例分析"，文中的讲解内容简单清晰，易于学习与理解，下面请大家跟着小编的思路慢慢深入，一起来研究和学习"solidity整型溢出举例分析"吧！

什么是整型溢出呢？在solidity编写合约时，定义整型一般是用uint8, uint256。一个变量如果定义为uint8表示的无符号的8位整型，即取值范围为0-255。当给这个变量赋值256时，即整型溢出变成了0，以此类推257变成了1。

pragma solidity ^0.4.24;//author: netkiller //homepage: http://www.netkiller.cncontract NetkillerOverflowTest{        function add(uint8 a, uint8 b) pure public returns (uint8){                uint8 result = a + b;                return result;            }        function sub(uint8 a, uint8 b) pure public returns (uint8){                uint8 result = a - b;                return result;            }        function mul(uint8 a, uint8 b) pure public returns (uint8){                uint8 result = a * b;                return result;            }        function div(uint8 a, uint8 b) pure public returns (uint8){                uint8 result = a / b;                return result;            }    }

调用上面合约，运行结果

254 + 1 = 255254 + 2 = 0254 + 3 = 1

减法运行结果

10 - 20 = 246

乘法运行结果

51 * 5 = 25551 * 6 = 50

再来测试乘法

255 / 10 = 25

这有点想千年虫问题，即99年变成00年后，你无法区分1900年还是2000年。

现在测试一下uint256，uint256支持的取值范围是0到2^256-1

pragma solidity ^0.4.24;//author: netkiller //homepage: http://www.netkiller.cncontract TestUint256Overflow {    // (2**256 - 1) + 1 = 0 向上溢出测试    function overflow() pure public returns (uint256 _overflow) {        uint256 max = 2 ** 256 - 1;        return max + 1;    }    // 0 - 1 = 2**256 - 1 向下溢出测试    function underflow() pure public returns (uint256 _underflow) {        uint256 min = 0;        return min - 1;    }}

运行结果

_overflow : 0_underflow : 115792089237316195423570985008687907853269984665640564039457584007913129639935

第一个函数溢出为 0，第二个函数 0 - 1 = 115792089237316195423570985008687907853269984665640564039457584007913129639935

解决溢出问题使用SafeMath库

pragma solidity ^0.4.24;//author: netkiller //homepage: http://www.netkiller.cnlibrary SafeMath {  function mul(uint256 a, uint256 b) internal pure returns (uint256 c) {    if (a == 0) {      return 0;    }    c = a * b;    assert(c / a == b);    return c;  }  function div(uint256 a, uint256 b) internal pure returns (uint256) {    return a / b;  }  function sub(uint256 a, uint256 b) internal pure returns (uint256) {    assert(b <= a);    return a - b;  }  function add(uint256 a, uint256 b) internal pure returns (uint256 c) {    c = a + b;    assert(c >= a);    return c;  }}contract NetkillerSafeMath {     using SafeMath for uint256;            function add(uint256 a, uint256 b) pure public returns (uint256){        uint256 result = a.add(b);        return result;    }    function sub(uint256 a, uint256 b) pure public returns (uint256){        uint256 result = a.sub(b);        return result;    }    function mul(uint256 a, uint256 b) pure public returns (uint256){        uint256 result = a.mul(b);        return result;    }    function div(uint256 a, uint256 b) pure public returns (uint256){        uint256 result = a.div(b);        return result;    }}

测试 SafeMath

add(115792089237316195423570985008687907853269984665640564039457584007913129639934,1)  => 115792089237316195423570985008687907853269984665640564039457584007913129639935add(115792089237316195423570985008687907853269984665640564039457584007913129639935,1)  => 抛出异常

感谢各位的阅读，以上就是"solidity整型溢出举例分析"的内容了，经过本文的学习后，相信大家对solidity整型溢出举例分析这一问题有了更深刻的体会，具体使用情况还需要大家实践验证。这里是，小编将为大家推送更多相关知识点的文章，欢迎关注！