ethereum - Solidity Remix 简单问题

Question

我是 Solidity 新手，这是我正在测试和重新混合的代码

browser/Untitled.sol:1:1: : 源文件未指定所需的编译器版本!考虑添加“pragma Solidity ^0.4.12契约(Contract) C {^跨越多行。

希望有人能指导一下。

contract C {
    function bytes32ToString(bytes32 x) constant returns (string) {
        bytes memory bytesString = new bytes(32);
        uint charCount = 0;
        for (uint j = 0; j < 32; j++) {
            byte char = byte(bytes32(uint(x) * 2 ** (8 * j)));
            if (char != 0) {
                bytesString[charCount] = char;
                charCount++;
            }
        }
        bytes memory bytesStringTrimmed = new bytes(charCount);
        for (j = 0; j < charCount; j++) {
            bytesStringTrimmed[j] = bytesString[j];
        }
        return string(bytesStringTrimmed);
    }

    function bytes32ArrayToString(bytes32[] data) returns (string) {
        bytes memory bytesString = new bytes(data.length * 32);
        uint urlLength;
        for (uint i=0; i<data.length; i++) {
            for (uint j=0; j<32; j++) {
                byte char = byte(bytes32(uint(data[i]) * 2 ** (8 * j)));
                if (char != 0) {
                    bytesString[urlLength] = char;
                    urlLength += 1;
                }
            }
        }
        bytes memory bytesStringTrimmed = new bytes(urlLength);
        for (i=0; i<urlLength; i++) {
            bytesStringTrimmed[i] = bytesString[i];
        }
        return string(bytesStringTrimmed);
    }     }

Answer 1

在源文件的最顶部包含版本编译指示以消除警告。

pragma solidity ^0.4.0;

contract MyContract {

}

来自Solidity documentation :

Version Pragma

Source files can (and should) be annotated with a so-called version pragma to reject being compiled with future compiler versions that might introduce incompatible changes. We try to keep such changes to an absolute minimum and especially introduce changes in a way that changes in semantics will also require changes in the syntax, but this is of course not always possible. Because of that, it is always a good idea to read through the changelog at least for releases that contain breaking changes, those releases will always have versions of the form 0.x.0 or x.0.0.

The version pragma is used as follows:

pragma solidity ^0.4.0;

Such a source file will not compile with a compiler earlier than version 0.4.0 and it will also not work on a compiler starting from version 0.5.0 (this second condition is added by using ^). The idea behind this is that there will be no breaking changes until version 0.5.0, so we can always be sure that our code will compile the way we intended it to. We do not fix the exact version of the compiler, so that bugfix releases are still possible.