I want to know which one uses less memory, I tried looking for it but didn't get a accurate answer.
Say I have a thousand instances of a C struct, which of the following would be better to sign a state?
orCode:unsigned myvar : 1;
Thank you for your time.Code:bool myvar;
Find out for yourself: sizeof( bool ) or sizeof( unsinged char )
Actually I see you are using a bit field. In either case, you still won't end up smaller than one byte.
Quzah.
Last edited by quzah; 06-23-2011 at 04:46 PM.
Hope is the first step on the road to disappointment.
Ah I see.
Thank you for your time.
'unsigned' without a type is equivalent to 'unsigned int'
Even if you only declare 1 bit of a bit field it still takes up sizeof(underlying type) bytes. In your case sizeof(unsigned int).
The main purpose* of a bit field is to pack multiple smaller variables in to a bigger "container-like" type. For example, you could fit 8 "bool-type" variables in to a single byte to save space or to simplify access to individual bits.
*) as far as I know, there might be other uses I am oblivious to
Edit: Also, isn't bool a C++ type? gcc says "error: ‘bool’ undeclared (first use in this function)" even with --std=c99
Edit2: Apparently it's called _Bool in gcc, and it's valid for all the C standards.. o_O
Last edited by _Mike; 06-23-2011 at 05:14 PM.
It's in C99, but you've got to include the magic header which is <stdbool.h>
Thank you.Originally Posted by tabstop
printf("%d\n", sizeof(bool)); gives a weird warning when compiling with -Wall:
test.c:16:2: warning: format ‘%d’ expects type ‘int’, but argument 2 has type ‘long unsigned int’
So the compiler thinks bool is an long unsigned int, but sizeof(bool) says 1.. hmm, interesting
No. What sizeof produces is a "long unsigned int" in your case. Not what type bool is.Thank you.
printf("%d\n", sizeof(bool)); gives a weird warning when compiling with -Wall:
test.c:16:2: warning: format ‘%d’ expects type ‘int’, but argument 2 has type ‘long unsigned int’
So the compiler thinks bool is an long unsigned int, but sizeof(bool) says 1.. hmm, interesting
Quzah.
Hope is the first step on the road to disappointment.
Actually no mike.... printf("%d\n",sizeof(bool)) will see the return type of sizeof()... not the type of bool.
printf("%u\n",sizeof(bool)); should print 1.
Haha yeah, just ignore my last post. I just realized my mistake and came back to edit it before someone got a chance to see it. I say stupid things without thinking far to often
Mistakes are how we learn. Even if we don't learn from them, someone else might.
Quzah.
Hope is the first step on the road to disappointment.
The size_t format spec in C99 is %zu. Doesn't matter here but if you're printing multiple things and sizeof(size_t) != sizeof(unsigned) weird things'll happen.
Absolutely... I made a mistake once, in 1977... and I'll never forget it!Mistakes are how we learn. Even if we don't learn from them, someone else might.
Quzah.
Interresting... I just looked that up, and it's duly filed under "Ya learns something new everyday"...
This looks like a place for a quote
Or, at the risk of quoting my father...
"I never make the same mistake twice. I'm always too busy making new ones".
