blocks|key|1558071|text|break会中断一个循环，但您可以向外部循环添加检查，该检查会在内部循环中断时中断。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1558072|bool+dobreak+=+false;
for+(+..;+!dobreak+&&+..;+..+)+{
+++for+(+...+)+{
++++++if+(...)+{
+++++++++dobreak+=+true;
+++++++++break;
++++++}
+++}
}|code-block|syntax|javascript|1558073|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

break breaks out of one loop, but you can add a check to the outer loop which breaks when the inner breaks.

<pre><code>bool dobreak = false;
for ( ..; !dobreak &amp;&amp; ..; .. ) {
 for ( ... ) {
 if (...) {
 dobreak = true;
 break;
 }
 }
}
</code></pre>

blocks|key|1342879|text|如果使用goto简化了代码，那么它将是合适的。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1342880|for+(;;)+
{
++++for+(;;)+
++++{
++++++++break;+/*+breaks+inner+loop+*/
++++}+
++++for+(;;)+
++++{
++++++++goto+outer;+/*+breaks+outer+loop+*/
++++}
}+
outer:;|code-block|syntax|javascript|1342881|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

If using goto simplifies the code, then it would be appropriate.

<pre><code>for (;;) 
{
 for (;;) 
 {
 break; /* breaks inner loop */
 } 
 for (;;) 
 {
 goto outer; /* breaks outer loop */
 }
} 
outer:;
</code></pre>

blocks|key|1558389|text|break语句只能让您跳出最内层的循环。如果您不希望在代码、内存和专用状态变量的性能方面增加额外的开销，我建议将代码重构为它自己的函数或方法，并使用return来摆脱所有循环：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1558390|void+do_lots_of_work(void)
{
++int+i,+j;

++for(i=0;+i<10+;+i%2B%2B)
++{
++++for(j=0;j<+10;+j%2B%2B)
++++{
+++++..
+++++..
+++++if(disaster_struck())
++++++return;+/*+Gets+us+out+of+the+loops,+and+the+function+too.+*/
++++}
++}
}|code-block|syntax|javascript|1558391|entityMap^0|0|5|22|6|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@$9|N|A|O|B|C]|$9|P|A|Q|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|R|8|@]|D|@]|E|$I|J]]|$1|K|3|-4|5|6|7|S|8|@]|D|@]|E|$]]]|L|$]]

The <code>break</code> statement only gets you out of the innermost loop. If you don't want the added overhead in code, memory and performance of a dedicated state variable, I recommend refactoring the code out into a function or method of its own, and using <code>return</code> to get out of all the loops:

<pre><code>void do_lots_of_work(void)
{
 int i, j;

 for(i=0; i&lt;10 ; i++)
 {
 for(j=0;j&lt; 10; j++)
 {
 ..
 ..
 if(disaster_struck())
 return; /* Gets us out of the loops, and the function too. */
 }
 }
}
</code></pre>

blocks|key|1342940|text|除了前面提到的标志变量或goto之外，你还可以throw一个Objective-C异常：|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1342941|@try+{
++for()+{
++++for()+{
+++++++@throw+...
++++}
++}
}
@catch{
++...
}|code-block|syntax|javascript|1342942|entityMap|0|LINK|mutability|MUTABLE|url|http://developer.apple.com/documentation/Cocoa/Conceptual/Exceptions/Tasks/RaisingExceptions.html^0|N|5|0|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@$A|R|B|S|1|T]]|C|$]]|$1|D|3|E|5|F|7|U|8|@]|9|@]|C|$G|H]]|$1|I|3|-4|5|6|7|V|8|@]|9|@]|C|$]]]|J|$K|$5|L|M|N|C|$O|P]]]]

Other than the already mentioned flag variable or goto you could <a href="http://developer.apple.com/documentation/Cocoa/Conceptual/Exceptions/Tasks/RaisingExceptions.html" rel="noreferrer">throw</a> an Objective-C exception:

<pre><code>@try {
 for() {
 for() {
 @throw ...
 }
 }
}
@catch{
 ...
}
</code></pre>

blocks|key|1342912|text|其他人提到了如何设置标志或使用goto，但我建议重构代码，以便将内部循环转换为单独的方法。然后，该方法可以返回一些标志，以指示外部循环应该break。如果您适当地命名您的方法，这将更具可读性。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1342913|for+(int+i+=+0;+i+<+10;+i%2B%2B)+{
+++if+(timeToStop(i))+break;
}

-(bool)+timeToStop:+(int)+i+{
++++for+(int+j+=+0;+j+<+10;+j%2B%2B)+{
++++++++if+(somethingBadHappens)+return+true;
++++}

++++return+false;
}|code-block|syntax|javascript|1342914|伪代码，未经过测试，但您已经明白了。|1342915|entityMap^0|F|4|1X|5|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@$9|P|A|Q|B|C]|$9|R|A|S|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|T|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|U|8|@]|D|@]|E|$]]|$1|M|3|-4|5|6|7|V|8|@]|D|@]|E|$]]]|N|$]]

Others have mentioned how you can set a flag or use a <code>goto</code>, but I'd recommend refactoring your code so that the inner loop is turned into a separate method. That method can then return some flag to indicate that the outer loop should <code>break</code>. If you name your methods appropriately, this is much more readable.

<pre><code>for (int i = 0; i &lt; 10; i++) {
 if (timeToStop(i)) break;
}

-(bool) timeToStop: (int) i {
 for (int j = 0; j &lt; 10; j++) {
 if (somethingBadHappens) return true;
 }

 return false;
}
</code></pre>

Pseudocode, not tested, but you get the idea.

blocks|key|1342781|text|break语句只会中断作用域中的循环，这是父循环。如果您也想跳出第二个循环，您可以使用一个布尔变量，该变量位于两个循环的范围内|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1342782|bool+isTerminated+=+false;

for+(...)
{
++++if+(!isTerminated)
++++{
++++++++for(...)
++++++++{
++++++++++++...

++++++++++++isTerminated+=+true;
++++++++++++break;
++++++++}
++++}
++++else
++++{
++++++++break;
++++}
}|code-block|syntax|javascript|1342783|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

The break statement will only break out of the loop in scope, which is the parent loop. If you want to break out of the second loop as well you could use a boolean variable which is in scope of both loops

<pre><code>bool isTerminated = false;

for (...)
{
 if (!isTerminated)
 {
 for(...)
 {
 ...

 isTerminated = true;
 break;
 }
 }
 else
 {
 break;
 }
}
</code></pre>

blocks|key|1342813|text|可能最简单的方法是使用"flag“变量|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1342814|for(i=0;+i<10+&&+(done==false);+i%2B%2B)
++for(j=0;j<+10;+j%2B%2B){
+++++..
+++++..
+++++if(...){done=true;+break;}
++}|code-block|syntax|javascript|1342815|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

Probably the easiest way is to use a "flag" variable 

<pre><code>for(i=0; i&lt;10 &amp;&amp; (done==false); i++)
 for(j=0;j&lt; 10; j++){
 ..
 ..
 if(...){done=true; break;}
 }
</code></pre>

blocks|key|1342833|text|在中断前更改顶部循环的计数器|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1342834|for(i=0;+i<10+;+i%2B%2B)
++for(j=0;j<+10;+j%2B%2B){
+++++..
+++++..
+++++i+=+10;+
+++++break;
++}|code-block|syntax|javascript|1342835|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

Change top loop's counter before break

<pre><code>for(i=0; i&lt;10 ; i++)
 for(j=0;j&lt; 10; j++){
 ..
 ..
 i = 10; 
 break;
 }
</code></pre>

blocks|key|1558502|text|另一种解决方案是分解函数中的第二个循环：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1558503|int+i;

for(i=0;+i<10+;+i%2B%2B){
++++if+!innerLoop(i)+{
++++++++break;
++++}
}

bool+innerLoop(int+i)
++++int+j;
++++for(j=0;j<+10;+j%2B%2B){
++++++++doSomthing(i,j);
++++++++if(endcondtion){
++++++++++++return+false;
++++++++}
++++}
}|code-block|syntax|javascript|1558504|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

Another solution is to factor out the second loop in a function:

<pre><code>int i;

for(i=0; i&lt;10 ; i++){
 if !innerLoop(i) {
 break;
 }
}

bool innerLoop(int i)
 int j;
 for(j=0;j&lt; 10; j++){
 doSomthing(i,j);
 if(endcondtion){
 return false;
 }
 }
}
</code></pre>

blocks|key|1558328|text|break语句打破了最内层的循环。需要一个额外的test和break语句来中断外部循环。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1558329|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

The break statement breaks out of the innermost loop. An additional test and break statement would be needed to break out of the outer loop.

blocks|key|1342713|text|如果从一组嵌套循环中执行break，则只终止在其中执行break的最内层循环。(就像标准C一样)|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1342714|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

If a break is executed from within a set of nested loops, only the innermost loop in which the break is executed is terminated. (Just like standard C)

blocks|key|1558522|text|和前几个一模一样，大体是这样的：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1558523|for(i=0;i<a;i%2B%2B){++
+for(j=0;j<a;j%2B%2B){
++if(Something_goes_wrong){
+++i=a;
+++break;
+++}
+}
}|code-block|syntax|javascript|1558524|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

Exactly like the last ones are, generally like this:

<pre><code>for(i=0;i&lt;a;i++){ 
 for(j=0;j&lt;a;j++){
 if(Something_goes_wrong){
 i=a;
 break;
 }
 }
}
</code></pre>

blocks|key|1558590|text|只是为了笑一笑，如何将这个真/假检查更改为一个方法并使用return语句：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1558591|-+(bool)+checkTrueFalse:+parameters{

+++for+(+...)+{
++++++for+(+...+)+{

+++++++++if+(...)+{
++++++++++++return+true;
+++++++++}

++++++}
+++}
+++return+false;
}|code-block|syntax|javascript|1558592|entityMap^0|S|6|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@$9|N|A|O|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|P|8|@]|D|@]|E|$I|J]]|$1|K|3|-4|5|6|7|Q|8|@]|D|@]|E|$]]]|L|$]]

Just for grins, how about changing this true/false check into a method and using <code>return</code> statements:

<pre><code>- (bool) checkTrueFalse: parameters{

 for ( ...) {
 for ( ... ) {

 if (...) {
 return true;
 }

 }
 }
 return false;
}
</code></pre>

I have two for loops nested like this:

<pre><code>for(...) {
 for(...) {

 }
}
</code></pre>

I know that there is a <code>break</code> statement. But I am confused about if it breaks both loops or just the one in which it was called? I need to break both ones as soon as I see that it doesn't make sense to iterate more times over.

How can I break out of two nested for loops in Objective-C?

Objective-C

我有两个这样嵌套的for循环：for(...) {    for(...) {    }}我知道有一个break语句。但我搞不懂它是中断了两个循环，还是只中断了被调用的那个循环？一旦我发现迭代更多的次数是没有意义的，我就需要同时打破这两种方法。

问如何在Objective-C中打破两个嵌套的for循环？
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回答 13

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问如何在Objective-C中打破两个嵌套的for循环？EN

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问如何在Objective-C中打破两个嵌套的for循环？
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