void pointer arithmetic error [duplicate]

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Pointer arithmetic for void pointer in C (10 answers)

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I am getting the unknown size error from the code below,

    atmel_device_info_t *info;

    int *ptr = row->offset + (void *) info

It is a casting problem, what should I do to fix the error? thank you for your help.

Answer 1

You cannot portably do arithmetic with a void * pointer. This makes sense, since it's a pointer to an unknown type of data, that data has no intrinsic size. The size of the pointed-to data is a central part of doing arithmetic.

usually a "byte" pointer works:

int *ptr = (int *) ((unsigned char *) info + row->offset);

The above assumes that row->offset is a byte offset, not an int offset. If you want the latter, cast accordingly:

int *ptr = (int *) info + row->offset;