blocks|key|627657|text|你的第一个问题纯粹是一个语法问题。这是无效的C：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|627658|int+[10]+A;|code-block|syntax|javascript|627659|它应该是：|627660|int+A[10];|627661|pthread_t+[10]+th;也是如此。|offset|length|style|CODE|627662|entityMap^0|0|0|0|0|0|I|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|T|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|U|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|V|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|W|8|@$M|X|N|Y|O|P]]|9|@]|A|$]]|$1|Q|3|-4|5|6|7|Z|8|@]|9|@]|A|$]]]|R|$]]

Your first problem is purely a syntax one. This is not valid C:

<pre><code>int [10] A;
</code></pre>

It should be:

<pre><code>int A[10];
</code></pre>

Similarly for <code>pthread_t [10] th;</code>.

blocks|key|633332|text|除了@Oli+Charlesworth的回答之外，srand不返回任何值，它被声明为void，所以您不能编写srand(time(0))+%25+20。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|633333|entityMap^0|P|5|16|4|1I|J|0^^$0|@$1|2|3|4|5|6|7|H|8|@$9|I|A|J|B|C]|$9|K|A|L|B|C]|$9|M|A|N|B|C]]|D|@]|E|$]]|$1|F|3|-4|5|6|7|O|8|@]|D|@]|E|$]]]|G|$]]

In addition to @Oli Charlesworth's answer, <code>srand</code> does not return any values, it's declared as <code>void</code>, so you can't write <code>srand(time(0)) % 20</code>.

blocks|key|207919|text|在编写int+[10]+A时，看起来您有一个Java背景(或D)。你可以把它理解为A是一个10整型数组对象的变量。但在C中，这些东西有点不同。在C中，只有单独的原始变量，它们可以排列在连续的内存集合中，这就称为一个数组。这就是为什么选择语法int+A[10];的原因，这意味着：A是一个指向整数的指针，指向自动分配给10个整数的存储的开始。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|207920|程序的下一个问题是通过void*类型传递整数，尽管编译器不会报告它。在C中，每个指针都可以转换为某个整数，但并不是所有的整数值都是指针。C中的指针是抽象的东西:大多数实现选择使用内存地址作为其整数表示。但通过内射LUT映射它们也是有效的。因此，一些整数值可能无法映射到指针，因此无法正确传输。你真的应该传递一个真正的指针。|207921|此外，您对线程的使用也是次优的。在您的例子中，您正在像mad一样丢弃缓存线，并且切换开销将吞噬所有的并行化收益。根据经验，您创建的线程数不应超过‘数量’%2B2个线程。考虑到所有这些因素，您可以执行以下操作：|BOLD|207922|#include+<stdio.h>
#include+<stdlib.h>
#include+<pthread.h>

/*+some+prime+number,+so+show+what+happens+with+uneven+work+sizes+*/
#define+ELEMENTS+17

int+M;
int+A[ELEMENTS];

struct+WorkletInfo+{
+++int+*data_base;
+++int+count;
};

void+*worklet(void+*t)
{
+++int+i;
+++struct+WorkletInfo+*wi+=+t;+/*+note:+no+cast+here+*/
+++if(!wi)
+++++++return+0;

+++for(i=0;+i+<+wi->count;+i%2B%2B)
+++++++wi->data_base[i]+*=+M;

+++return+wi;
}

#define+N_CPUS+4
#define+NUM_THREADS+(N_CPUS%2B1)

int+main(int+argc,+char+*argv[])
{
+++int+t,+ec;
+++pthread_t+th[NUM_THREADS];
+++int+remaining_elements;
+++int+const+elements_per_worklet+=+ELEMENTS/NUM_THREADS;

+++srand(time(0));
+++M=rand();

+++/*+you+must+initialize+the+data+a+thread+will+access+before+starting+the+thread+*/
+++for(t+=+0;+t+<+ELEMENTS;+t%2B%2B)
+++++++A[t]=t%2B1;+/*+0+*+x+=+0,+so+give+it+some+nonzero+value+*/

+++remaining_elements+=+ELEMENTS+-+(elements_per_worklet*NUM_THREADS);
+++ec+=+0;
+++for(t+=+0;+t+<+NUM_THREADS;+t%2B%2B)
+++{
+++++++struct+WorkletInfo+*wi+=+malloc(sizeof(*wi));
+++++++wi->data_base+=+&A[ec];

+++++++wi->count+=+elements_per_worklet;
+++++++if(t<remaining_elements)+{
+++++++++++wi->count%2B%2B;
+++++++}
+++++++ec+%2B=+wi->count;

+++++++pthread_create(&th[t],+NULL,+worklet,+wi);
+++}

+++ec+=+0;
+++for(t+=+0;+t+<+NUM_THREADS;+t%2B%2B)
+++{
+++++++int+i;
+++++++struct+WorkletInfo+*wi;
+++++++void+*retval;
+++++++pthread_join(th[t],+&retval);

+++++++if(!retval)
+++++++++++continue;

+++++++wi+=+retval;

+++++++for(i+=+0;+i+<+wi->count;+i%2B%2B,+ec%2B%2B)
+++++++++++printf("worklet+%25d,+worklet+element+%25d+=>+total+element+%25d:++%25d\n",+
++++++++++++++t,+i,+ec,+
++++++++++wi->data_base[i]);

+++++++free(wi);
+++++++}

+++printf("Thread+main\n");

+++return+0;
}|code-block|syntax|javascript|207923|此程序的输出如下所示：|207924|worklet+0,+worklet+element+0+=>+total+element+0:++300787748
worklet+0,+worklet+element+1+=>+total+element+1:++601575496
worklet+0,+worklet+element+2+=>+total+element+2:++902363244
worklet+1,+worklet+element+0+=>+total+element+3:++1203150992
worklet+1,+worklet+element+1+=>+total+element+4:++1503938740
worklet+1,+worklet+element+2+=>+total+element+5:++1804726488
worklet+1,+worklet+element+3+=>+total+element+6:++2105514236
worklet+2,+worklet+element+0+=>+total+element+7:++-1888665312
worklet+2,+worklet+element+1+=>+total+element+8:++-1587877564
worklet+2,+worklet+element+2+=>+total+element+9:++-1287089816
worklet+3,+worklet+element+0+=>+total+element+10:++-986302068
worklet+3,+worklet+element+1+=>+total+element+11:++-685514320
worklet+3,+worklet+element+2+=>+total+element+12:++-384726572
worklet+3,+worklet+element+3+=>+total+element+13:++-83938824
worklet+4,+worklet+element+0+=>+total+element+14:++216848924
worklet+4,+worklet+element+1+=>+total+element+15:++517636672
worklet+4,+worklet+element+2+=>+total+element+16:++818424420
Thread+main+exit|207925|entityMap^0|3|A|15|1|3C|A|3V|1|0|B|5|0|20|7|0|0|0|0^^$0|@$1|2|3|4|5|6|7|V|8|@$9|W|A|X|B|C]|$9|Y|A|Z|B|C]|$9|10|A|11|B|C]|$9|12|A|13|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|14|8|@$9|15|A|16|B|C]]|D|@]|E|$]]|$1|H|3|I|5|6|7|17|8|@$9|18|A|19|B|J]]|D|@]|E|$]]|$1|K|3|L|5|M|7|1A|8|@]|D|@]|E|$N|O]]|$1|P|3|Q|5|6|7|1B|8|@]|D|@]|E|$]]|$1|R|3|S|5|M|7|1C|8|@]|D|@]|E|$N|O]]|$1|T|3|-4|5|6|7|1D|8|@]|D|@]|E|$]]]|U|$]]

It looks like you're having a Java background (or D), as you wrote <code>int [10] A</code>. You may read this as <code>A</code> is a variable to a array of 10 ints type object. But in C those things are a little bit different. In C there are only individual primitive variables, and they may be arranged in sets of continous memory, which is then called an array. That's why the syntax <code>int A[10];</code> was choosen, which means: <code>A</code> is a pointer to integer, pointing the beginning of automatically allocated storage for 10 integers.

The next problem with your program, though the compiler will not report it is passing an integer through a <code>void*</code> type. In C every pointer can be converted to some integer, but not all integer values make pointers. Pointers in C are abstract things: Most implementations choose to use the memory address as their integer representation. But it would be as valid to map them through a injective LUT. So some integer values may not map to a pointer and thus not properly transfer. You should really pass a real pointer.

Also your use of threads is suboptimal. In your case you're trashing cache lines like mad and the switching overhead will eat up any parallelization gain. As a rule of thumb you should create no more than 'number of CPU cores' + 2 threads. Taking all this into account you could do the following:

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

/* some prime number, so show what happens with uneven work sizes */
#define ELEMENTS 17

int M;
int A[ELEMENTS];

struct WorkletInfo {
 int *data_base;
 int count;
};

void *worklet(void *t)
{
 int i;
 struct WorkletInfo *wi = t; /* note: no cast here */
 if(!wi)
 return 0;

 for(i=0; i &lt; wi-&gt;count; i++)
 wi-&gt;data_base[i] *= M;

 return wi;
}

#define N_CPUS 4
#define NUM_THREADS (N_CPUS+1)

int main(int argc, char *argv[])
{
 int t, ec;
 pthread_t th[NUM_THREADS];
 int remaining_elements;
 int const elements_per_worklet = ELEMENTS/NUM_THREADS;

 srand(time(0));
 M=rand();

 /* you must initialize the data a thread will access before starting the thread */
 for(t = 0; t &lt; ELEMENTS; t++)
 A[t]=t+1; /* 0 * x = 0, so give it some nonzero value */

 remaining_elements = ELEMENTS - (elements_per_worklet*NUM_THREADS);
 ec = 0;
 for(t = 0; t &lt; NUM_THREADS; t++)
 {
 struct WorkletInfo *wi = malloc(sizeof(*wi));
 wi-&gt;data_base = &amp;A[ec];

 wi-&gt;count = elements_per_worklet;
 if(t&lt;remaining_elements) {
 wi-&gt;count++;
 }
 ec += wi-&gt;count;

 pthread_create(&amp;th[t], NULL, worklet, wi);
 }

 ec = 0;
 for(t = 0; t &lt; NUM_THREADS; t++)
 {
 int i;
 struct WorkletInfo *wi;
 void *retval;
 pthread_join(th[t], &amp;retval);

 if(!retval)
 continue;

 wi = retval;

 for(i = 0; i &lt; wi-&gt;count; i++, ec++)
 printf("worklet %d, worklet element %d =&gt; total element %d: %d\n", 
 t, i, ec, 
 wi-&gt;data_base[i]);

 free(wi);
 }

 printf("Thread main\n");

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

The output of this program looks like this:

<pre><code>worklet 0, worklet element 0 =&gt; total element 0: 300787748
worklet 0, worklet element 1 =&gt; total element 1: 601575496
worklet 0, worklet element 2 =&gt; total element 2: 902363244
worklet 1, worklet element 0 =&gt; total element 3: 1203150992
worklet 1, worklet element 1 =&gt; total element 4: 1503938740
worklet 1, worklet element 2 =&gt; total element 5: 1804726488
worklet 1, worklet element 3 =&gt; total element 6: 2105514236
worklet 2, worklet element 0 =&gt; total element 7: -1888665312
worklet 2, worklet element 1 =&gt; total element 8: -1587877564
worklet 2, worklet element 2 =&gt; total element 9: -1287089816
worklet 3, worklet element 0 =&gt; total element 10: -986302068
worklet 3, worklet element 1 =&gt; total element 11: -685514320
worklet 3, worklet element 2 =&gt; total element 12: -384726572
worklet 3, worklet element 3 =&gt; total element 13: -83938824
worklet 4, worklet element 0 =&gt; total element 14: 216848924
worklet 4, worklet element 1 =&gt; total element 15: 517636672
worklet 4, worklet element 2 =&gt; total element 16: 818424420
Thread main exit
</code></pre>

the question is:
to write program with global integer one dimensional array A of size N by a factor M. using threads , the main thread initializes A and M with random integers, creates N threads such that the ith thread finds Ai = M * Ai, and finally prints the array A.

my problem i am having an error with array initialization also i am not sure about making the threads in correct way.
i hope i explained my problem clearly. 

<pre><code>#include &lt;stdio.h&gt;
#include &lt;stdlib.h&gt;
#include &lt;pthread.h&gt;
int M;
int [10] A;

void *run(void *t)
{
 A[(int)t]=A[(int)t]*M;
 pthread_exit(NULL);
}


int main()
{
 pthread_t [10] th;
 srand(time(0))%20;
 M=rand();
 int t;
 for(t = 0; t &lt; 10; t++)
 {
 pthread_create(&amp;th[t], NULL, run, (void *)t);
 }

 int j;
 for(j=0;j&lt;10;j++)
 A[j]=j;

 int i;
 for(i = 0; i &lt; 10; i++)
 {
 pthread_join(th[i], NULL);
 printf("%d: %d\n", i,A[i]);
 }

 printf("Thread main\n");
 pthread_exit(NULL);
}
</code></pre>

these are the errors:

<pre><code>que1.c:5: error: expected identifier or ‘(’ before ‘[’ token
que1.c: In function ‘run’:
que1.c:9: error: ‘A’ undeclared (first use in this function)
que1.c:9: error: (Each undeclared identifier is reported only once
que1.c:9: error: for each function it appears in.)
que1.c: In function ‘main’:
que1.c:16: error: expected identifier or ‘(’ before ‘[’ token
que1.c:17: error: void value not ignored as it ought to be
que1.c:22: error: ‘th’ undeclared (first use in this function)
que1.c:27: error: ‘A’ undeclared (first use in this function)
</code></pre>

how to use threads and array in C

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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问题是:编写全局整数大小为N的一维数组A的程序的因子M。使用线程，主线程用随机整数初始化A和M，创建N个线程，使得第i个线程找到Ai =M* Ai，最后打印数组A。我的问题是，我有一个数组初始化的错误，我也不确定以正确的方式制作线程。我希望我已经把我的问题解释清楚了。#include <stdio.h>#include...

问如何在C++中使用线程和数组
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