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POUnix Programming Shared Memory strange results
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  1. POUnix Programming Shared Memory strange results
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    copied!<p>I have been working on semaphores and shared memory for a week now, and have some difficulties yet,so i tried to make this program which the children are supposed to write to a memory shared multidimensional integer array and the father is suppose to read that array from the memory that is shared.</p> <pre><code>#include &lt;stdio.h&gt; #include &lt;stdlib.h&gt; #include &lt;unistd.h&gt; #include &lt;sys/ipc.h&gt; #include &lt;sys/shm.h&gt; #include &lt;stdio.h&gt; #include &lt;sys/fcntl.h&gt; #include &lt;semaphore.h&gt; #include &lt;sys/wait.h&gt; #define MAXCHILDS 1 #define MAX_SIZE 10 #define MAX_WRITES 100 typedef struct{ int m[MAX_SIZE][MAX_SIZE]; }matrix; /*fork variables*/ pid_t child[MAXCHILDS]; /*semphores variables */ sem_t *empty, *full, * mutex; /*share memory id*/ int shmid; /*shared memory array pointer */ matrix * sh_mem; void init(){ /*semaphores unlink and creation */ sem_unlink("EMPTY"); empty=sem_open("EMPTY",O_CREAT|O_EXCL,0700,50); sem_unlink("FULL"); full=sem_open("FULL",O_CREAT|O_EXCL,0700,0); sem_unlink("MUTEX"); mutex=sem_open("MUTEX",O_CREAT|O_EXCL,0700,1); /*initialize shared memory */ shmid = shmget(IPC_PRIVATE,sizeof(matrix),IPC_CREAT|0777); /*map shared memory*/ sh_mem = (matrix*)shmat(shmid,NULL,0); if(sh_mem == (matrix*)(-1)){ perror("shmat"); } } void writer(int m[MAX_SIZE][MAX_SIZE],int n_child){ int i,k; for(i = 0;i&lt;MAX_SIZE;i++){ for(k= 0;k&lt;MAX_SIZE;k++){ m[i][k] = 0; if(i==(k+1)){ m[i][k] = 1; } } } } void reader(int m[MAX_SIZE][MAX_SIZE]){ int i = 0; int k = 0; int sum = 0; for(i = 0;i&lt;MAX_SIZE;i++){ for(k= 0;k&lt;MAX_SIZE;k++){ printf("%d",m[k][i]); } sum++; printf("[i=]%d[k=]%d\n",i,k); } printf("%d",sum); } void terminate() { sem_close(empty); sem_close(full); sem_close(mutex); sem_unlink("EMPTY"); sem_unlink("FULL"); sem_unlink("MUTEX"); shmctl(shmid, IPC_RMID, NULL); } int main(int argc, char **argv) { int i,sum; init(); for(i = 0;i&lt;MAXCHILDS;i++){ if((child[i]= fork()) &lt; 0) // error occured { perror("Fork Failed"); exit(1); } if((child[i] =fork())==0){ writer(sh_mem-&gt;m,i); exit(0); } } /*father*/ sleep(10); sum++; printf("%d\n",sum); reader(sh_mem-&gt;m); wait(NULL); terminate(); return 0; } </code></pre> <p>I have two problems right now ... I need to save the array to a memory mapped file which i dont seem to understand and the output of the father is throwing is very strange ...His output is </p> <pre><code>0000100000[i=]3[k=]10 0000010000[i=]4[k=]10 0000001000[i=]5[k=]10 0100000000[i=]0[k=]10 0000000100[i=]6[k=]10 0010000000[i=]1[k=]10 0000000010[i=]7[k=]10 0001000000[i=]2[k=]10 0000000001[i=]8[k=]10 0000100000[i=]3[k=]10 0000000000[i=]9[k=]10 0000010000[i=]4[k=]10 0000001000[i=]5[k=]10 0000000100[i=]6[k=]10 0000000010[i=]7[k=]10 0000000001[i=]8[k=]10 0000000000[i=]9[k=]10 </code></pre> <p>And it should be something like this:</p> <pre><code>0000100000[i=]0[k=]10 0000010000[i=]1[k=]10 0000001000[i=]2[k=]10 0100000000[i=]3[k=]10 0000000100[i=]4[k=]10 0010000000[i=]5[k=]10 0000000010[i=]6[k=]10 0001000000[i=]7[k=]10 0000000001[i=]8[k=]10 0000100000[i=]9[k=]10 </code></pre>
 

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