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POShared memory program not synchronized - Giving segmentation faults
 

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  1. POShared memory program not synchronized - Giving segmentation faults
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    <p>I am trying to use shared memory with 2 programs which I have shown here. a and b are integer arrays and array1 and array2 are arrays of strings. This is the snippet first program which loads the data in the memory</p> <pre><code>int size = (NUMBER_OF_DATA*(sizeof(int)+sizeof(float))); key_t key1, key2, key3; key1 = ftok("/home/an/Desktop/newww.c", 4); key2 = ftok("/home/an/Desktop/part1.c", 5); key3 = ftok("/home/an/Desktop/part2.c", 6); int shmid = shmget(key1, size, 0777|IPC_CREAT); int shmid1 = shmget(key2, 20*NUMBER_OF_DATA, 0777|IPC_CREAT); int shmid2 = shmget(key3, 20*NUMBER_OF_DATA, 0777|IPC_CREAT); int *a = (int *)shmat(shmid, 0, 0); float *b = (float *)(a + NUMBER_OF_DATA); char **array1 = (char **)shmat(shmid1, 0, 0); printf("array1 %p\n", &amp;array1); char *mempos = (char *)(array1 + NUMBER_OF_DATA); printf("MEMPOS %p\n", &amp;mempos); char **array2 = (char **)shmat(shmid2, 0, 0); char *mempos1 = (char *)(array2 + (NUMBER_OF_DATA)); for(i=0; i&lt;NUMBER_OF_DATA; i++) { a[i] = a[i]; b[i] = b[i]; array1[i] = mempos; strcpy(array1[i], array1[i]); mempos += 20; array2[i] = mempos1; strcpy(array2[i], array2[i]); mempos1 += 20; printf("%p %p %p %p\n", &amp;a[i], &amp;b[i], array1[i], array2[i]); } j = 0; while (j&lt;5) { j++; for (i=0; i&lt;NUMBER_OF_DATA; i++) { printf("%s %s %d %f\n", array1[i], array2[i], a[i], b[i]); } printf("\n"); sleep(2); } </code></pre> <p>I am trying to load some data in the shared memory by the above file and alter the elements in the shared memory by the file below. But as soon as I update a string in the file below, I get garbage values from the program above instead of the altered values. I am totally confused. Have tried debugging with gdb but everything looks okay there. </p> <pre><code>int size = (NUMBER_OF_DATA*(sizeof(int)+sizeof(float))) + (2*(20*NUMBER_OF_DATA)); key_t key1, key2, key3; key1 = ftok("/home/an/Desktop/newww.c", 4); key2 = ftok("/home/an/Desktop/part1.c", 5); key3 = ftok("/home/an/Desktop/part2.c", 6); int shmid = shmget(key1, size, 0777|IPC_CREAT); int shmid1 = shmget(key2, 20*NUMBER_OF_DATA, 0777|IPC_CREAT); int shmid2 = shmget(key3, 20*NUMBER_OF_DATA, 0777|IPC_CREAT); int *a = (int *)shmat(shmid, 0, 0); float *b = (float *)(a + NUMBER_OF_DATA); char **array1 = (char **)shmat(shmid1, 0, 0); printf("array1 %p\n", &amp;array1); char *mempos = (char *)(array1 + NUMBER_OF_DATA); printf("MEMPOS %p\n", &amp;mempos); char **array2 = (char **)shmat(shmid2, 0, 0); char *mempos1 = (char *)(array2 + (NUMBER_OF_DATA)); int i; for(i=0; i&lt;5; i++) { printf("enter\n"); array1[i] = mempos; scanf("%s", array1[i]); mempos += 20; } </code></pre> <p>What is the solution?</p>
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    1. This table or related slice is empty.
    1. PTQuestion
    1. USedgar.holleis
    1. USNidhi Dwivedi
    plurals
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. PO
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      1. PTAnswer
    1. VO
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      1. POShared memory program not synchronized - Giving segmentation faults
      1. This table or related slice is empty.
      1. VTDownMod
    2. VO
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      1. POShared memory program not synchronized - Giving segmentation faults
      1. This table or related slice is empty.
      1. VTUpMod
    1. COwhy are you not using the [boot shared memory library](http://www.boost.org/doc/libs/1_52_0/doc/html/interprocess/sharedmemorybetweenprocesses.html)?
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      1. POShared memory program not synchronized - Giving segmentation faults
      1. USdrone.ah
    2. COI don't see any error checking in your code whatsoever - how do you even know that all your calls to `shmget`, `shmat`, etc are successful ?
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      1. POShared memory program not synchronized - Giving segmentation faults
      1. USPaul R
    3. CO@drone.ah: it's tagged `c`, so boost is presumably not an option (otherwise I'd agree with you - `boost::interprocess` is the way to go for C++)
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      1. POShared memory program not synchronized - Giving segmentation faults
      1. USPaul R
 

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