C++核心准则ES.77：循环中尽量少用break和continue
C++核心准则ES.77：循环中尽量少用break和continue
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<T> 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<T> &vec)
{
for (const T &item : vec) {
if (/* some condition*/) return item;
}
return T(); //default value
}
void use2()
{
std::vector<T> 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