C Initialize Struct with a loop

Question

Below I have the code for a struct in a program I'm writing. I would like to be able to initialize these parameters in some sort of loop, but I can't seem to figure out how to configure the .water/.air/.purge properties to update with the loop. nozzle_count is 16 so I would like to find a way to achieve the code below without having to just copy and paste it 16 times. I'd appreciate any input. Thanks!

static nozzle nozzles[nozzle_count] = {
    {
        .water = C1_WATER, .air = C1_AIR, .purge = C1_PURGE,
        .interval = 15*60*1000, .cycle = 0*3*5*1000, .purge_length = 0*4*1000,
        .state = WAIT
    },
    {
        .water = C2_WATER, .air = C2_AIR, .purge = C2_PURGE,
        .interval = 2*60*1000, .cycle = 1*3*1000, .purge_length = 0*4*1000,
        .state = WAIT
    },
    {
        .water = C3_WATER, .air = C3_AIR, .purge = C3_PURGE,
        .interval = 2*60*1000, .cycle = 0*1*5*1000, .purge_length = 0*4*1000,
        .state = WAIT
    }
    {
        .water = C4_WATER, .air = C4_AIR, .purge = C4_PURGE,
        .interval = 2*60*1000, .cycle = 0*1*5*1000, .purge_length = 0*4*1000,
        .state = WAIT
    }
    {
        .water = C5_WATER, .air = C5_AIR, .purge = C5_PURGE,
        .interval = 2*60*1000, .cycle = 0*1*5*1000, .purge_length = 0*4*1000,
        .state = WAIT
    }
};

It's conceivably possible in C++ with constexpr and/or template magic, but yeah, in C you'd be limited to truly terrible recursive macros, where the cure is worse than the disease. — ShadowRanger
– ShadowRanger, Commented Jul 23, 2018 at 23:06
If some (or all) values are potentially different and irregular then there's no meaningful way to use a loop here. Why would you even want a loop? What would be the point? — AnT stands with Russia
– AnT stands with Russia, Commented Jul 23, 2018 at 23:13
interval and cycle appear to change. Is that by accident? If not, how do you derive those values? — c1moore
– c1moore, Commented Jul 23, 2018 at 23:14
Show the definitions of C1_WATER, C1_AIR, C2_WATER etc. — M.M
– M.M, Commented Jul 23, 2018 at 23:14

Joseph Quinsey · Accepted Answer · 2018-07-23 23:41:56Z

I think your code looks perfectly fine, even if the length of your array is increased from 5 to 16. Two possible suggestions.

If you remove the C99 initialization fluff, then everything can fit into a single line:

static nozzle nozzles[nozzle_count] = {
//    water     air     purge     interval    cycle       purge_length state
//    --------  ------  --------  ----------  ----------  ------------ ----
    { C1_WATER, C1_AIR, C1_PURGE, 15*60*1000, 0*3*5*1000, 0*4*1000,    WAIT },
//  ...
};

This is a simple table, just 16 lines long, which is clear and obvious and which is easy-to-maintain.

Secondly, if you need to keep the per-member initialization, you could enclose it a macro, which helps with DRY:

#define FOO(a, b, c, d, e, f, g)                                 \
    {                                                            \
       .water = (a), .air = (b), .purge = (c),                   \
       .interval = (d), .cycle = (e),  .purge_length = (f),      \
       .state = (b)                                              \
    }

static nozzle nozzles[nozzle_count] = {
//    water     air     purge     interval    cycle       purge_length state
//    --------  ------  --------  ----------  ----------  ------------ ----
 FOO( C1_WATER, C1_AIR, C1_PURGE, 15*60*1000, 0*3*5*1000, 0*4*1000,    WAIT ),
//  ...
};

0___________ · Accepted Answer · 2018-07-23 23:23:54Z

1

The only workaround I can think of is:

const TYPE_OF_CxPURGE PURGE[] = {...};
const TYPE_OF_CxAIR AIR[] = {....};
const TYPE_OF_CxWATER WATER[] = {....};

And somewhere in the code

for(size_t index = 0; index < sizeof(nozzles) / sizeof(nozzles[0]); index ++)
{
    nozzles.water = WATER[index];
    nozzles.air = AIR[index]; 
    nozzles.purge = PURGE[index];
    nozzles.interval = 15*60*1000; 
    nozzles.cycle = 0*3*5*1000; 
    nozzles.purge_length = 0*4*1000,
    nozzles.state = WAIT
}

But I think that the normal initialization is better. Only 16 elements. If you have more just write the script to generate this initialization code

answered Jul 23, 2018 at 23:23

0___________

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Comments

Joy Allen · Accepted Answer · 2018-07-24 02:08:29Z

0

Can you show the definition of *_WATER, *_AIR, *_PURGE?

for (i = 0; i < nozzle_count; i++)
{
    nozzles[i] = (struct nozzle){WATER[i], AIR[i], PURGE[i], 15*60*1000, 0, 0, WAIT};
}

answered Jul 24, 2018 at 2:08

Joy Allen

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