C++核心准则ES.41: 如果对操作符的优先级有疑问，使用括号明确运算次序

ES.41: If in doubt about operator precedence, parenthesize

ES.41: 如果对操作符的优先级有疑问，使用括号明确运算次序

Reason（原因）

Avoid errors. Readability. Not everyone has the operator table memorized.

避免错误。可读性。不是所有人都记住操作符表。

Example（示例）

const unsigned int flag = 2;
unsigned int a = flag;

if (a & flag != 0)  // bad: means a&(flag != 0)

Note: We recommend that programmers know their precedence table for the arithmetic operations, the logical operations, but consider mixing bitwise logical operations with other operators in need of parentheses.

注意：我们建议程序员记住数学运算，逻辑运算的优先级（而不适用括号，译者注）。但认为位操作和其他操作符混用时应该使用括号。

if ((a & flag) != 0)  // OK: works as intended

Note（注意）

You should know enough not to need parentheses for:

你应该可以理解下面的代码不需要括号。

if (a < 0 || a <= max) {
    // ...
}

Enforcement（实施建议）

• Flag combinations of bitwise-logical operators and other operators.
• 标记将位操作和其他操作混用的情况。
• Flag assignment operators not as the leftmost operator.
• 标记赋值运算符不在最左侧的情况。
• ???

链接

https://github.com/isocpp/CppCoreGuidelines/blob/master/CppCoreGuidelines.md#es40-avoid-complicated-expressions