ES.45: Avoid "magic constants"; use symbolic constants
ES.45:避免“魔法常數”,使用符號化常量
Reason(原因)
Unnamed constants embedded in expressions are easily overlooked and often hard to understand:
表達式中的無名常量很容易被忽視,通常也難於理解。
Example(示例)
for (int m = 1; m <= 12; ++m) // don't: magic constant 12
cout << month[m] << '\n';
No, we don't all know that there are 12 months, numbered 1..12, in a year. Better:
不是所有人都知道都理解數字1...12指的是一年中的12個月。好一點的寫法是:
// months are indexed 1..12
constexpr int first_month = 1;
constexpr int last_month = 12;
for (int m = first_month; m <= last_month; ++m) // better
cout << month[m] << '\n';
Better still, don't expose constants:
不暴露常量也是比較好的做法:
for (auto m : month)
cout << m << '\n';
Enforcement(實施建議)
Flag literals in code. Give a pass to 0, 1, nullptr, \n, "", and others on a positive list.
標記代碼中的字面量。但是允許0,1,nullptr,\n,“”,還有其他包括在正面清單中的字面量。
原文鏈接
https://github.com/isocpp/CppCoreGuidelines/blob/master/CppCoreGuidelines.md#es45-avoid-magic-constants-use-symbolic-constants
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