C++核心准则ES.77:循环中尽量少用break和continue-技术圈

ES.77: Minimize the use of break and continue in loops

ES.77：循环中尽量少用break和continue

Reason（原因）

In a non-trivial loop body, it is easy to overlook a break or a continue.

A break in a loop has a dramatically different meaning than a break in a switch-statement (and you can have switch-statement in a loop and a loop in a switch-case).

在不规整的循环体中，很容易忽略掉break和continue。循环中的break和switch语句中的break存在显著的不同（同时你还可以将在循环体内放入switch语句或者在switch语句中放入循环。）

Example（示例）

switch(x) {
case 1 :
    while (/* some condition */) {
        //...
    break;
    } //Oops! break switch or break while intended?
case 2 :
    //...
    break;
}

Alternative（可选项）

Often, a loop that requires a break is a good candidate for a function (algorithm), in which case the break becomes a return.

需要break的循环通常很适合做成函数（算法），这是break可以变成return。

//Original code: break inside loop
void use1()
{
    std::vector vec = {/* initialized with some values */};
    T value;
    for (const T item : vec) {
        if (/* some condition*/) {
            value = item;
            break;
        }
    }
    /* then do something with value */
}

//BETTER: create a function and return inside loop
T search(const std::vector &vec)
{
    for (const T &item : vec) {
        if (/* some condition*/) return item;
    }
    return T(); //default value
}

void use2()
{
    std::vector vec = {/* initialized with some values */};
    T value = search(vec);
    /* then do something with value */
}

Often, a loop that uses continue can equivalently and as clearly be expressed by an if-statement.

通常，使用continue的循环可以等价地，清晰地表示为if语句。

for (int item : vec) { //BAD
    if (item%2 == 0) continue;
    if (item == 5) continue;
    if (item > 10) continue;
    /* do something with item */
}

for (int item : vec) { //GOOD
    if (item%2 != 0 && item != 5 && item <= 10) {
        /* do something with item */
    }
}

Note（注意）

If you really need to break out a loop, a break is typically better than alternatives such as modifying the loop variable or a goto:

如果你确实需要终端一个循环，break通常会优于修改循环变量或goto语句。

Enforcement（实施建议）

???

原文链接

https://github.com/isocpp/CppCoreGuidelines/blob/master/CppCoreGuidelines.md#es77-minimize-the-use-of-break-and-continue-in-loops

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