blocks|key|1446643|text|C没有foreach，但是宏经常被用来模拟它：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1446644|#define+for_each_item(item,+list)+\
++++for(T+*+item+=+list->head;+item+!=+NULL;+item+=+item->next)|code-block|syntax|javascript|1446645|并且可以像这样使用|1446646|for_each_item(i,+processes)+{
++++i->wakeup();
}|1446647|数组上的迭代也是可能的：|1446648|#define+foreach(item,+array)+\
++++for(int+keep+=+1,+\
++++++++++++count+=+0,\
++++++++++++size+=+sizeof+(array)+/+sizeof+*(array);+\
++++++++keep+&&+count+!=+size;+\
++++++++keep+=+!keep,+count%2B%2B)+\
++++++for(item+=+(array)+%2B+count;+keep;+keep+=+!keep)|1446649|1446650|int+values[]+=+{+1,+2,+3+};
foreach(int+*v,+values)+{
++++printf("value:+%25d\n",+*v);
}|1446651|编辑:如果您对C%2B%2B解决方案也感兴趣，C%2B%2B有一个原生的for-each语法，称为"range+based+for“。|1446652|entityMap^0|0|0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|V|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|W|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|X|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|Y|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|Z|8|@]|9|@]|A|$]]|$1|M|3|N|5|D|7|10|8|@]|9|@]|A|$E|F]]|$1|O|3|H|5|6|7|11|8|@]|9|@]|A|$]]|$1|P|3|Q|5|D|7|12|8|@]|9|@]|A|$E|F]]|$1|R|3|S|5|6|7|13|8|@]|9|@]|A|$]]|$1|T|3|-4|5|6|7|14|8|@]|9|@]|A|$]]]|U|$]]

C doesn't have a foreach, but macros are frequently used to emulate that:

<pre><code>#define for_each_item(item, list) \
 for(T * item = list-&gt;head; item != NULL; item = item-&gt;next)
</code></pre>

And can be used like

<pre><code>for_each_item(i, processes) {
 i-&gt;wakeup();
}
</code></pre>

Iteration over an array is also possible:

<pre><code>#define foreach(item, array) \
 for(int keep = 1, \
 count = 0,\
 size = sizeof (array) / sizeof *(array); \
 keep &amp;&amp; count != size; \
 keep = !keep, count++) \
 for(item = (array) + count; keep; keep = !keep)
</code></pre>

And can be used like

<pre><code>int values[] = { 1, 2, 3 };
foreach(int *v, values) {
 printf("value: %d\n", *v);
}
</code></pre>

Edit: In case you are also interested in C++ solutions, C++ has a native for-each syntax called "range based for"

blocks|key|1446700|text|以下是C99中for-each宏的完整程序示例：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1446701|#include+<stdio.h>

typedef+struct+list_node+list_node;
struct+list_node+{
++++list_node+*next;
++++void+*data;
};

#define+FOR_EACH(item,+list)+\
++++for+(list_node+*(item)+=+(list);+(item);+(item)+=+(item)->next)

int
main(int+argc,+char+*argv[])
{
++++list_node+list[]+=+{
++++++++{+.next+=+&list[1],+.data+=+"test+1"+},
++++++++{+.next+=+&list[2],+.data+=+"test+2"+},
++++++++{+.next+=+NULL,+++++.data+=+"test+3"+}
++++};

++++FOR_EACH(item,+list)
++++++++puts((char+*)+item->data);

++++return+0;
}|code-block|syntax|javascript|1446702|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|$]]

Here is a full program example of a for-each macro in C99:

<pre><code>#include &lt;stdio.h&gt;

typedef struct list_node list_node;
struct list_node {
 list_node *next;
 void *data;
};

#define FOR_EACH(item, list) \
 for (list_node *(item) = (list); (item); (item) = (item)-&gt;next)

int
main(int argc, char *argv[])
{
 list_node list[] = {
 { .next = &amp;list[1], .data = "test 1" },
 { .next = &amp;list[2], .data = "test 2" },
 { .next = NULL, .data = "test 3" }
 };

 FOR_EACH(item, list)
 puts((char *) item-&gt;data);

 return 0;
}
</code></pre>

blocks|key|1446517|text|在C中没有foreach。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1446518|您可以使用for循环遍历数据，但需要知道长度或数据需要由已知值终止(例如，空)。|1446519|char*+nullTerm;
nullTerm+=+"Loop+through+my+characters";

for(;nullTerm+!=+NULL;nullTerm%2B%2B)
{
++++//nullTerm+will+now+point+to+the+next+character.
}|code-block|syntax|javascript|1446520|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|L|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|M|8|@]|9|@]|A|$G|H]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

There is no foreach in C.

You can use a for loop to loop through the data but the length needs to be know or the data needs to be terminated by a know value (eg. null).

<pre><code>char* nullTerm;
nullTerm = "Loop through my characters";

for(;nullTerm != NULL;nullTerm++)
{
 //nullTerm will now point to the next character.
}
</code></pre>

blocks|key|1661517|text|这是一个相当古老的问题，但我想我应该把这个贴出来。这是一个用于GNU+C99的foreach循环。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1661518|#include+<stdio.h>
#include+<stdlib.h>
#include+<string.h>
#include+<stdbool.h>

#define+FOREACH_COMP(INDEX,+ARRAY,+ARRAY_TYPE,+SIZE)+\
++__extension__+\
++({+\
++++bool+ret+=+0;+\
++++if+(__builtin_types_compatible_p+(const+char*,+ARRAY_TYPE))+\
++++++ret+=+INDEX+<+strlen+((const+char*)ARRAY);+\
++++else+\
++++++ret+=+INDEX+<+SIZE;+\
++++ret;+\
++})

#define+FOREACH_ELEM(INDEX,+ARRAY,+TYPE)+\
++__extension__+\
++({+\
++++TYPE+*tmp_array_+=+ARRAY;+\
++++&tmp_array_[INDEX];+\
++})

#define+FOREACH(VAR,+ARRAY)+\
for+(void+*array_+=+(void*)(ARRAY);+array_;+array_+=+0)+\
for+(size_t+i_+=+0;+i_+&&+array_+&&+FOREACH_COMP+(i_,+array_,+\
++++++++++++++++++++++++++++++++++++__typeof__+(ARRAY),+\
++++++++++++++++++++++++++++++++++++sizeof+(ARRAY)+/+sizeof+((ARRAY)[0]));+\
++++++++++++++++++++++++++++++++++++i_%2B%2B)+\
for+(bool+b_+=+1;+b_;+(b_)+?+array_+=+0+:+0,+b_+=+0)+\
for+(VAR+=+FOREACH_ELEM+(i_,+array_,+__typeof__+((ARRAY)[0]));+b_;+b_+=+0)

/*+example's+*/
int
main+(int+argc,+char+**argv)
{
++int+array[10];
++/*+initialize+the+array+*/
++int+i+=+0;
++FOREACH+(int+*x,+array)
++++{
++++++*x+=+i;
++++++%2B%2Bi;
++++}

++char+*str+=+"hello,+world!";
++FOREACH+(char+*c,+str)
++++printf+("%25c\n",+*c);

++return+EXIT_SUCCESS;
}|code-block|syntax|javascript|1661519|这段代码已经过测试，可以在GNU/Linux上与gcc、icc和clang一起使用。|1661520|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|L|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|M|8|@]|9|@]|A|$]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

This is a fairly old question, but I though I should post this. It is a foreach loop for GNU C99.

<pre><code>#include &lt;stdio.h&gt;
#include &lt;stdlib.h&gt;
#include &lt;string.h&gt;
#include &lt;stdbool.h&gt;

#define FOREACH_COMP(INDEX, ARRAY, ARRAY_TYPE, SIZE) \
 __extension__ \
 ({ \
 bool ret = 0; \
 if (__builtin_types_compatible_p (const char*, ARRAY_TYPE)) \
 ret = INDEX &lt; strlen ((const char*)ARRAY); \
 else \
 ret = INDEX &lt; SIZE; \
 ret; \
 })

#define FOREACH_ELEM(INDEX, ARRAY, TYPE) \
 __extension__ \
 ({ \
 TYPE *tmp_array_ = ARRAY; \
 &amp;tmp_array_[INDEX]; \
 })

#define FOREACH(VAR, ARRAY) \
for (void *array_ = (void*)(ARRAY); array_; array_ = 0) \
for (size_t i_ = 0; i_ &amp;&amp; array_ &amp;&amp; FOREACH_COMP (i_, array_, \
 __typeof__ (ARRAY), \
 sizeof (ARRAY) / sizeof ((ARRAY)[0])); \
 i_++) \
for (bool b_ = 1; b_; (b_) ? array_ = 0 : 0, b_ = 0) \
for (VAR = FOREACH_ELEM (i_, array_, __typeof__ ((ARRAY)[0])); b_; b_ = 0)

/* example's */
int
main (int argc, char **argv)
{
 int array[10];
 /* initialize the array */
 int i = 0;
 FOREACH (int *x, array)
 {
 *x = i;
 ++i;
 }

 char *str = "hello, world!";
 FOREACH (char *c, str)
 printf ("%c\n", *c);

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

This code has been tested to work with gcc, icc and clang on GNU/Linux.

blocks|key|1446948|text|虽然C没有for+each结构，但它总是有一个惯用的表示，表示数组(&arr)[1]的末尾。这允许您为每个循环编写一个简单的惯用法，如下所示：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1446949|int+arr[]+=+{1,2,3,4,5};
for(int+*a+=+arr;+a+<+(&arr)[1];+%2B%2Ba)
++++printf("%25d\n",+*a);|code-block|syntax|javascript|1446950|entityMap^0|X|9|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|$]]

While C does not have a for each construct, it has always had an idiomatic representation for one past the end of an array <code>(&amp;arr)[1]</code>. This allows you to write a simple idiomatic for each loop as follows:

<pre><code>int arr[] = {1,2,3,4,5};
for(int *a = arr; a &lt; (&amp;arr)[1]; ++a)
 printf("%d\n", *a);
</code></pre>

blocks|key|1661348|text|C有“for”和“while”两个关键字。如果像C#这样的语言中的foreach语句看起来像这样...|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1661349|foreach+(Element+element+in+collection)
{
}|code-block|syntax|javascript|1661350|..。那么这个foreach语句在C中的等价物可能如下所示：|1661351|for+(
++++Element*+element+=+GetFirstElement(&collection);
++++element+!=+0;
++++element+=+GetNextElement(&collection,+element)
++++)
{
++++//TODO:+do+something+with+this+element+instance+...
}|1661352|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|N|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|O|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

C has 'for' and 'while' keywords. If a foreach statement in a language like C# looks like this ...

<pre><code>foreach (Element element in collection)
{
}
</code></pre>

... then the equivalent of this foreach statement in C might be be like:

<pre><code>for (
 Element* element = GetFirstElement(&amp;collection);
 element != 0;
 element = GetNextElement(&amp;collection, element)
 )
{
 //TODO: do something with this element instance ...
}
</code></pre>

blocks|key|1446797|text|当你使用"break“或"continue”时，Eric's+answer不起作用。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1446798|这可以通过重写第一行来修复：|1446799|原始行(重新格式化)：|1446800|for+(unsigned+i+=+0,+__a+=+1;+i+<+B.size();+i%2B%2B,+__a+=+1)|code-block|syntax|javascript|1446801|已修复：|1446802|for+(unsigned+i+=+0,+__a+=+1;+__a+&&+i+<+B.size();+i%2B%2B,+__a+=+1)|1446803|如果你将它与约翰斯的循环进行比较，你会发现他实际上也在做同样的事情，只是更复杂，更丑陋。|1446804|entityMap|0|LINK|mutability|MUTABLE|url|https://stackoverflow.com/a/1236910/419^0|O|D|0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|10|8|@]|9|@$A|11|B|12|1|13]]|C|$]]|$1|D|3|E|5|6|7|14|8|@]|9|@]|C|$]]|$1|F|3|G|5|6|7|15|8|@]|9|@]|C|$]]|$1|H|3|I|5|J|7|16|8|@]|9|@]|C|$K|L]]|$1|M|3|N|5|6|7|17|8|@]|9|@]|C|$]]|$1|O|3|P|5|J|7|18|8|@]|9|@]|C|$K|L]]|$1|Q|3|R|5|6|7|19|8|@]|9|@]|C|$]]|$1|S|3|-4|5|6|7|1A|8|@]|9|@]|C|$]]]|T|$U|$5|V|W|X|C|$Y|Z]]]]

<a href="https://stackoverflow.com/a/1236910/419">Eric's answer</a> doesn't work when you're using "break" or "continue". 

This can be fixed by rewriting the first line:

Original line (reformatted):

<pre><code>for (unsigned i = 0, __a = 1; i &lt; B.size(); i++, __a = 1)
</code></pre>

Fixed:

<pre><code>for (unsigned i = 0, __a = 1; __a &amp;&amp; i &lt; B.size(); i++, __a = 1)
</code></pre>

If you compare it to Johannes' loop, you'll see that he's actually doing the same, just a bit more complicated and uglier.

blocks|key|1661604|text|下面是一个简单的for循环：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1661605|#define+FOREACH(type,+array,+size)+do+{+\
++++++++type+it+=+array[0];+\
++++++++for(int+i+=+0;+i+<+size;+i%2B%2B,+it+=+array[i])
#define+ENDFOR++}+while(0);

int+array[]+=+{+1,+2,+3,+4,+5+};

FOREACH(int,+array,+5)
{
++++printf("element:+%25d.+index:+%25d\n",+it,+i);
}
ENDFOR|code-block|syntax|javascript|1661606|允许您访问索引(i)和我们正在迭代的当前项(it)。注在嵌套循环时，您可能会遇到命名问题，您可以将项目和索引名称设置为宏的参数。|offset|length|style|CODE|1661607|编辑:这是accepted+foreach的修改版本。允许您指定start索引，size，以便它在衰减的数组(指针)上工作，不需要int*，并将count+!=+size更改为i+<+size，以防用户意外地将'i‘修改为大于size并陷入无限循环。|1661608|#define+FOREACH(item,+array,+start,+size)\
++++for(int+i+=+start,+keep+=+1;\
++++++++keep+&&+i+<+size;\
++++++++keep+=+!keep,+i%2B%2B)\
++++for+(item+=+array[i];+keep;+keep+=+!keep)

int+array[]+=+{+1,+2,+3,+4,+5+};
FOREACH(int+x,+array,+2,+5)
++++printf("index:+%25d.+element:+%25d\n",+i,+x);|1661609|输出：|1661610|index:+2.+element:+3
index:+3.+element:+4
index:+4.+element:+5|1661611|entityMap^0|0|0|8|1|M|2|0|E|7|W|5|14|4|1T|4|20|D|2G|8|35|4|0|0|0|0^^$0|@$1|2|3|4|5|6|7|W|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|X|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|Y|8|@$I|Z|J|10|K|L]|$I|11|J|12|K|L]]|9|@]|A|$]]|$1|M|3|N|5|6|7|13|8|@$I|14|J|15|K|L]|$I|16|J|17|K|L]|$I|18|J|19|K|L]|$I|1A|J|1B|K|L]|$I|1C|J|1D|K|L]|$I|1E|J|1F|K|L]|$I|1G|J|1H|K|L]]|9|@]|A|$]]|$1|O|3|P|5|D|7|1I|8|@]|9|@]|A|$E|F]]|$1|Q|3|R|5|6|7|1J|8|@]|9|@]|A|$]]|$1|S|3|T|5|D|7|1K|8|@]|9|@]|A|$E|F]]|$1|U|3|-4|5|6|7|1L|8|@]|9|@]|A|$]]]|V|$]]

Here's a simple one, single for loop:

<pre><code>#define FOREACH(type, array, size) do { \
 type it = array[0]; \
 for(int i = 0; i &lt; size; i++, it = array[i])
#define ENDFOR } while(0);

int array[] = { 1, 2, 3, 4, 5 };

FOREACH(int, array, 5)
{
 printf("element: %d. index: %d\n", it, i);
}
ENDFOR
</code></pre>

Gives you access to the index should you want it (<code>i</code>) and the current item we're iterating over (<code>it</code>). Note you might have naming issues when nesting loops, you can make the item and index names be parameters to the macro.

Edit: Here's a modified version of the accepted answer <code>foreach</code>. Lets you specify the <code>start</code> index, the <code>size</code> so that it works on decayed arrays (pointers), no need for <code>int*</code> and changed <code>count != size</code> to <code>i &lt; size</code> just in case the user accidentally modifies 'i' to be bigger than <code>size</code> and get stuck in an infinite loop.

<pre><code>#define FOREACH(item, array, start, size)\
 for(int i = start, keep = 1;\
 keep &amp;&amp; i &lt; size;\
 keep = !keep, i++)\
 for (item = array[i]; keep; keep = !keep)

int array[] = { 1, 2, 3, 4, 5 };
FOREACH(int x, array, 2, 5)
 printf("index: %d. element: %d\n", i, x);
</code></pre>

Output:

<pre><code>index: 2. element: 3
index: 3. element: 4
index: 4. element: 5
</code></pre>

blocks|key|1661746|text|如果您计划使用函数指针|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1661747|#define+lambda(return_type,+function_body)\
++++({+return_type+__fn__+function_body+__fn__;+})

#define+array_len(arr)+(sizeof(arr)/sizeof(arr[0]))

#define+foreachnf(type,+item,+arr,+arr_length,+func)+{\
++++void+(*action)(type+item)+=+func;\
++++for+(int+i+=+0;+i<arr_length;+i%2B%2B)+action(arr[i]);\
}

#define+foreachf(type,+item,+arr,+func)\
++++foreachnf(type,+item,+arr,+array_len(arr),+func)

#define+foreachn(type,+item,+arr,+arr_length,+body)\
++++foreachnf(type,+item,+arr,+arr_length,+lambda(void,+(type+item)+body))

#define+foreach(type,+item,+arr,+body)\
++++foreachn(type,+item,+arr,+array_len(arr),+body)|code-block|syntax|javascript|1661748|用法：|1661749|int+ints[]+=+{+1,+2,+3,+4,+5+};
foreach(int,+i,+ints,+{
++++printf("%25d\n",+i);
});

char*+strs[]+=+{+"hi!",+"hello!!",+"hello+world",+"just",+"testing"+};
foreach(char*,+s,+strs,+{
++++printf("%25s\n",+s);
});

char**+strsp+=+malloc(sizeof(char*)*2);
strsp[0]+=+"abcd";
strsp[1]+=+"efgh";
foreachn(char*,+s,+strsp,+2,+{
++++printf("%25s\n",+s);
});

void+(*myfun)(int+i)+=+somefunc;
foreachf(int,+i,+ints,+myfun);|1661750|但我认为这只适用于gcc+(不确定)。|1661751|entityMap^0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|Q|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|R|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|S|8|@]|9|@]|A|$]]|$1|M|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|N|$]]

If you're planning to work with function pointers

<pre><code>#define lambda(return_type, function_body)\
 ({ return_type __fn__ function_body __fn__; })

#define array_len(arr) (sizeof(arr)/sizeof(arr[0]))

#define foreachnf(type, item, arr, arr_length, func) {\
 void (*action)(type item) = func;\
 for (int i = 0; i&lt;arr_length; i++) action(arr[i]);\
}

#define foreachf(type, item, arr, func)\
 foreachnf(type, item, arr, array_len(arr), func)

#define foreachn(type, item, arr, arr_length, body)\
 foreachnf(type, item, arr, arr_length, lambda(void, (type item) body))

#define foreach(type, item, arr, body)\
 foreachn(type, item, arr, array_len(arr), body)
</code></pre>

Usage:

<pre><code>int ints[] = { 1, 2, 3, 4, 5 };
foreach(int, i, ints, {
 printf("%d\n", i);
});

char* strs[] = { "hi!", "hello!!", "hello world", "just", "testing" };
foreach(char*, s, strs, {
 printf("%s\n", s);
});

char** strsp = malloc(sizeof(char*)*2);
strsp[0] = "abcd";
strsp[1] = "efgh";
foreachn(char*, s, strsp, 2, {
 printf("%s\n", s);
});

void (*myfun)(int i) = somefunc;
foreachf(int, i, ints, myfun);
</code></pre>

But I think this will work only on gcc (not sure).

Almost all languages have a <a href="https://en.wikipedia.org/wiki/Foreach_loop" rel="noreferrer"><code>foreach</code> loop</a> or something similar. Does C have one? Can you post some example code?

Does C have a "foreach" loop construct?

Linux

几乎所有的语言都有或类似的东西。C有吗？你能发布一些示例代码吗？

问C有"foreach“循环结构吗？
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回答 9

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问C有"foreach“循环结构吗？EN

回答 9

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问C有"foreach“循环结构吗？
EN