bool found = false;
    
    for(int i=0; i < m; ++i){
        for(int j=0; j < n; ++j)
            if(grid[i][j] == '*'){
                q.push(make_pair(i,j));
                found = true;
                break;
            }
        if(found)
            break;
    }

Breaking out of a for-loop is a little strange to me, since the semantics of a for-loop typically indicate that it will execute a specified number of times. However, it's not bad in all cases; if you're searching for something in a collection and want to break after you find it, it's useful. Breaking out of nested loops, however, isn't possible in C++; it is in other languages through the use of a labeled break. You can use a label and a goto, but that might give you heartburn at night..? Seems like the best option though.

我的建议是使用一个检查变量来打破一个期望的循环。结果代码可能不那么令人愉快。 您可以使用预处理器，以便在引擎盖下进行所需的破坏。这种方法可以隐藏丑陋的代码和额外的复杂性。 例如，我创建了自定义中断机制，如下所示:

想要的代码:

for (int i = 0; i < 100; i++) {
    for (int j = 0; j < 100; j++) {
        for (int k = 0; k < 100; k++) {
            //do something
            if (desiredCondition) {
                breakToLevel = 0;
            }
            if (breakToLevel < 3) {
                break;
            }
        }
        if (breakToLevel < 2) {
            break;
        }
    }
    if (breakToLevel < 1) {
        break;
    }
}

宏定义:

#define BREAK_TO(L) breakToLevel = (L); 
#define CHECK_BREAK(L) if (breakToLevel < (L)) break; 

和结果:

for (int i = 0; i < 100; i++) {
    for (int j = 0; j < 100; j++) {
        for (int k = 0; k < 100; k++) {
            //do something
            if (desiredCondition) {
                BREAK_TO(0)
            }
            CHECK_BREAK(3)
        }
        CHECK_BREAK(2)
    }
    CHECK_BREAK(1)
}

break语句终止它出现的最近的封闭do、for、switch或while语句的执行。控制权转移到终止语句后面的语句。

从msdn。

打破几个嵌套循环的一个好方法是将代码重构为一个函数:

void foo()
{
    for(unsigned int i=0; i < 50; i++)
    {
        for(unsigned int j=0; j < 50; j++)
        {
            for(unsigned int k=0; k < 50; k++)
            {
                // If condition is true
                return;
            }
        }
    }
}

你可以用try…catch。

try {
    for(int i=0; i<10; ++i) {
        for(int j=0; j<10; ++j) {
            if(i*j == 42)
                throw 0; // this is something like "break 2"
        }
    }
}
catch(int e) {} // just do nothing
// just continue with other code

如果必须同时跳出几个循环，通常会出现异常。