C++核心准则ES.10:每次只定义一个名称

ES.10: Declare one name (only) per declaration

ES.10:每次只定义一个名称

Reason（原因）

One declaration per line increases readability and avoids mistakes related to the C/C++ grammar. It also leaves room for a more descriptive end-of-line comment.

每行一个声明的做法可以提高可读性，避免C/C++语法相关的错误。也可以为描写性行末注释留出空间。

Example, bad（反面示例）

char *p, c, a[7], *pp[7], **aa[10];   // yuck!Exception

A function declaration can contain several function argument declarations.

函数声明可以包含多个参数声明。

Exception（例外）

A structured binding (C++17) is specifically designed to introduce several variables:

结构化绑定（C++17）是为引入多个变量而特别设计的。

auto [iter, inserted] = m.insert_or_assign(k, val);
if (inserted) { /* new entry was inserted */ }

Example（示例）

template <class InputIterator, class Predicate>
bool any_of(InputIterator first, InputIterator last, Predicate pred);

or better using concepts:

更好的选择是使用concepts：

bool any_of(InputIterator first, InputIterator last, Predicate pred);

Example（示例）

double scalbn(double x, int n);   // OK: x * pow(FLT_RADIX, n); FLT_RADIX is usually 2

or（或者）:

double scalbn(    // better: x * pow(FLT_RADIX, n); FLT_RADIX is usually 2
    double x,     // base value
    int n         // exponent
);

or（又或者）:

// better: base * pow(FLT_RADIX, exponent); FLT_RADIX is usually 2
double scalbn(double base, int exponent);

Example（示例）

int a = 7, b = 9, c, d = 10, e = 3;

In a long list of declarators it is easy to overlook an uninitialized variable.

如果是一长串声明，很容易漏掉某个没有初始化的变量。

Enforcement（实施建议）

Flag variable and constant declarations with multiple declarators (e.g., int* p, q;)

标记包含多个变量和常数的声明语句。

原文链接

https://github.com/isocpp/CppCoreGuidelines/blob/master/CppCoreGuidelines.md#es10-declare-one-name-only-per-declaration