c++ - Casting/dereferencing char pointers to a double array -


is there wrong casting double pointer char pointer? goal in following code change 1 element in 3 different ways.

double   vec1[100]; double   *vp = vec1; char     *yp = (char*) vp; vp++; vec1[1] = 19.0; *vp = 12.0; *((double*) (yp + (1*sizeof (vec1[0])))) = 34.0;

casts of type fall category of "ok if know you're doing dangerous if don't".

for example, in case know pointer value of "yp" (it pointing double) technically safe increase value size of double , re-cast double*.

a counter-example: suppose didn't know char* came from...say, given function parameter. now, cast big problem: since char* technically 1-byte-aligned , double 8-byte-aligned, can't sure if given 8-byte-aligned address. if it's aligned, arithmetic produce valid double*; if not, crash when dereferenced.

this 1 example of how casts can go wrong. you're doing (at first glance) looks work in general have pay attention when cast things.


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