How to attach an array of strings to shared memory? C

Question

Working with shared memory for the first time, my project is to have readers and writers access shared strings and modify or read them, etc. I know that malloc doesn't work but not sure how to attach a 2d string array to memory, i keep getting this from the compiler:

warning: assignment makes integer from pointer without a cast

    int array_id;                         // id for the shared memory segment
    char records[10][50];                // the shared memory segment array

    // attach the reader to the shared segment
    fread(&newrecord, sizeof(id_record), 1, id_file);
    array_id = newrecord.id;

    printf("%d\n", array_id);

    records[0][0] = (char**) shmat(array_id, (void*) 0, 0);
    if (records[0] == (void*)-1) {
            perror("Array Attachment Reader");
    }

arrayid is correct i've triple checked it don't bring it up.

thanks

Jonathan Leffler · Accepted Answer · 2012-11-11 19:08:36Z

4

You will need to attach the shared memory, but store the pointer:

char (*records)[10][50];   // Pointer to an array

records = shmat(array_id, (void *)0, 0);

if ((void *)records == (void *)-1) ...error...

strcpy((*records)[0], newrecord);

You were trying to change the address at which the records array is stored; C doesn't allow that.

answered Nov 11, 2012 at 19:08

Jonathan Leffler

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1 Comment

caf Over a year ago

You could also just use char (*records)[50] and then strcpy(records[0], newrecord);.

Omkant · Accepted Answer · 2012-11-11 19:13:43Z

1

Don't use like this because records[0][0] is of char type not (char**)

edited Nov 11, 2012 at 19:13

answered Nov 11, 2012 at 19:07

Omkant

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