# 十六進制字面量 十六進制字面量，以關鍵字`hex`打頭，后面緊跟用單或雙引號包裹的字符串。如`hex"001122ff"`。在內部會被表示為二進制流。通過下面的例子來理解下是什么意思： ``` pragma solidity ^0.4.0; contract HexLiteral{ function test() returns (string){ var a = hex"001122FF"; //var b = hex"A"; //Expected primary expression return a; } } ``` 由于一個字節是8位，所以一個`hex`是由兩個`[0-9a-z]`字符組成的。所以`var b = hex"A";`不是成雙的字符串是會報錯的。 ## 轉換 十六進制的字面量與字符串可以進行同樣的類似操作： ``` pragma solidity ^0.4.0; contract HexLiteralBytes{ function test() returns (bytes4, bytes1, bytes1, bytes1, bytes1){ bytes4 a = hex"001122FF"; return (a, a[0], a[1], a[2], a[3]); } } ``` 可以發現，它可以隱式的轉為`bytes`，上述代碼的執行結果如下： ``` Result: "0x001122ff00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000011000000000000000000000000000000000000000000000000000000000000002200000000000000000000000000000000000000000000000000000000000000ff00000000000000000000000000000000000000000000000000000000000000" Transaction cost: 21857 gas. Execution cost: 585 gas. Decoded: bytes4: 0x001122ff bytes1: 0x00 bytes1: 0x11 bytes1: 0x22 bytes1: 0xff ```