solidity基础-类型转换

隐式转换

发生场景

• 赋值
• 函数的传参
• 运算符

转换的标准

• 必须是值类型
• 源类型必须是目标类型的子集

显式转换

• uint / int

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.17;

contract Demo {

    /*
    * uint / int 从小转大，在二进制左侧补零
    * uint / int 从大转小，从右开始保留数据
    */
    uint16 public u1 = 300;
    uint32 public u2 = uint32(u1); // 300
    uint8 public u3 = uint8(u1); // 44
    
    int16 public u1 = 300;
    int32 public u2 = int32(u1); // 300
    int8 public u3 = int8(u1); // 44
    
}

• bytesN

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.17;

contract Demo {

    /*
     * bytes 从小转大，在二进制右侧补零
     * bytes 从大转小，从左开始保留数据
     */
    bytes3 public b1 = 0x616263; // 0x616263
    bytes4 public b2 = bytes4(b1); // 0x61626300
    bytes1 public b3 = bytes1(b1); // 0x61
    
}

• bytesN 与 uint 转换

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.17;

contract Demo {

    bytes2 public b1 = 0x6162; // 0x6162

    // 0x6162 => 110000101100010 => 01100010 => 98
    uint8 public u1 = uint8(uint16(b1)); // 98
    // 0x6162 => 0110000101100010 => 24930
    uint32 public u2 = uint32(uint16(b1)); // 24930
    // 0x6162 => 0x61 => 97
    uint8 public u3 = uint8(bytes1(b1)); // 97
    // 0x6162 => 0x61620000 => 1633812480
    uint32 public u4 = uint32(bytes4(b1)); // 1633812480


    uint16 public u5 = 24930;

    // 24930 => 100100100100110000 => 01100010 => 0x62
    bytes1 public b2 = bytes1(uint8(u5)); // 0x62
    // 24930 => 0x6162 => 0x61
    bytes1 public b3 = bytes1(bytes2(u5)); // 0x61
    // 24930 => 100100100100110000 => 0...0100100100100110000 => 0x00006162
    bytes4 public b4 = bytes4(uint32(u5)); // 0x00006162
    // 24930 => 0x6162 => 0x61620000
    bytes4 public b5 = bytes4(bytes2(u5)); // 0x61620000

}

• bytes / bytesN 转换

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.17;

contract Demo {

    bytes public b1 = hex"6162";

    bytes1 public bn1 = bytes1(b1); // 0x61
    bytes4 public bn4 = bytes4(b1); // 0x61620000

    function test() external pure returns (bytes memory) {
        bytes2 bn2 = 0x6162;
        bytes memory tmp = new bytes(2);
        for (uint8 i = 0; i < 2; i++) {
            tmp[i] = bn2[i];
        }
        return tmp; // 0x6162
    }

}

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