Initializing structs with memset

RE: Initializing structs with memset

Sensors — Tue, 30 Jun 2015 14:08:28 GMT

Just did a little experiment with this. There was no change in code size between the two approaches using Keil uVision (armcc).

RE: Initializing structs with memset

Charles Manning — Mon, 02 Mar 2015 02:50:54 GMT

I don't think that is quite true.

The {0} version will create a binary version of the structure and the = will cause a copy.

xx = {0};

is eqivalent to

y = {0};memcpy(&x,&y, sizeof(y));

;

But the result is the same: The code is larger (and slower) since making a large structure needs to make the huge structure then also do a copy. A copy requires reading then writing each word in the structure. That is slower than just setting it to zero.

RE: Initializing structs with memset

RK — Sat, 28 Feb 2015 03:09:58 GMT

Well there's style, and space.

ble_gatts_char_md_t char_md = {};

forces the compiler to emit code to explicitly set each element of the structure to zero when it's created, for large structures that's a fair amount of instructions. memset, which is usually linked in anyway, is just a function call, less code space.