first parameter in memset passing array or pointer
gcc 4.4.4 c89
Pointers are not the same as arrays. But arrays can decay into pointers.
I was just using memset which first parameter is a pointer. I would like to initialize my structure array.
i.e.
struct devices
{
char name[STRING_SIZE];
size_t profile;
char catagory;
};
struct devices dev[NUM_DEVICES];开发者_JAVA技巧
memset(dev, 0, (size_t)NUM_DEVICES * sizeof(*dev));
dev == &dev[0]
But should I pass the first parameter has this:
memset(&dev, 0, (size_t)NUM_DEVICES * sizeof(*dev));
Many thanks for any advice,
What you have:
memset(dev, 0, (size_t)NUM_DEVICES * sizeof(*dev));
is fine - you pass a pointer to the first element of the array, and the size of the array. However, the (size_t)
cast is unnecessary (sizeof
has type size_t
, so it will cause the correct promotion) and I find that dev[0]
is clearer than *dev
in this case:
memset(dev, 0, NUM_DEVICES * sizeof dev[0]);
Alternatively, you can use &dev
as the address. In this case, it is probably clearer to use sizeof dev
- the size of the whole array:
memset(&dev, 0, sizeof dev);
I say that this is clearer, because it's generally best to have the first parameter be a pointer to the type that's the subject of sizeof
in the last parameter: the memset()
should look like one of these forms:
memset(p, ..., N * sizeof p[0])
memset(&x, ..., sizeof x)
Note however that this last one only works if dev
really is an array - like it is in this case. If instead you have a pointer to the first element of the array, you'll need to use the first version.
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