C++核心准则ES.26: 不要将一个变量用于两个无关的用途

ES.26: Don't use a variable for two unrelated purposes

ES.26: 不要将一个变量用于两个无关的用途

Reason（原因）

Readability and safety.

可读性和安全性。

Example, bad（反面示例）

void use()
{
    int i;
    for (i = 0; i < 20; ++i) { /* ... */ }
    for (i = 0; i < 200; ++i) { /* ... */ } // bad: i recycled
}

Note（注意）

As an optimization, you may want to reuse a buffer as a scratch pad, but even then prefer to limit the variable's scope as much as possible and be careful not to cause bugs from data left in a recycled buffer as this is a common source of security bugs.

作为一种优化，你可能将buffer用作告诉暂存区，即使是这种用情况最好还是尽可能限定变量的作用域，而且注意不要因为留在循环使用的buffer中的数据引发错误。这是安全错误的一个常见来源。

void write_to_file() {
    std::string buffer;             // to avoid reallocations on every loop iteration
    for (auto& o : objects)
    {
        // First part of the work.
        generate_first_string(buffer, o);
        write_to_file(buffer);

        // Second part of the work.
        generate_second_string(buffer, o);
        write_to_file(buffer);

        // etc...
    }
}

Enforcement（实施建议）

Flag recycled variables.

标记循环使用的变量。

原文链接

https://github.com/isocpp/CppCoreGuidelines/blob/master/CppCoreGuidelines.md#es26-dont-use-a-variable-for-two-unrelated-purposes