How to initialize automatically an array of pointers to function?

Question

I have a set of functions:

int a1(int x, int, y)
{ do some stuff}

int a2(int x, int, y)
{ do some stuff}

//.........

int a100500(int x, int, y)
{ do some stuff}

Is there is a way to automatically initialize an array of pointers to function via FOR loop instead of explicitly typing a code like

int (*pfunc[100500])(int, int) = {a1, a2, ..., a1005000}

My first idea was to use #define directive in a following way:

#define z(n) a##n

// ..............

for (int i = 1; i< 100501;i++)
{ 
    pfunc[i] = z(i);
}

Unfortunately, z(i) becomes "ai" and not "a1", "a2", etc.

I hope, maybe some C-guru can help me with some advice.

boost has some macros to mock for loops in header; quite "ugly" but may help you if you really need it — OznOg
– OznOg, Commented May 23, 2019 at 14:45
OK, I gotta ask, why do you have 100k functions in the first place? Or rather, what’s your actual use-case? — Konrad Rudolph
– Konrad Rudolph, Commented May 23, 2019 at 14:45
@tenghiz That’s why I was asking (and am still interested in) actual use-cases. — Konrad Rudolph
– Konrad Rudolph, Commented May 23, 2019 at 14:49
10-15 entries can be populated "manually" with much less effort than using some esoteric tricks, which won't probably be much appreciated by your instructor. — Eugene Sh.
– Eugene Sh., Commented May 23, 2019 at 15:00
This is almost certainly an "XY problem". You are most likely using the wrong solution to the original problem you are trying to solve. — Lundin
– Lundin, Commented May 23, 2019 at 15:08

Aviv Goll · Accepted Answer · 2019-05-24 03:57:46Z

2

Expanding @Giacomo Catenazzi's comment, consider the following (not great) python script:

# generate_funcs.py
import sys
with open('funcs.inc', 'w') as f:
    f.write(',\n'.join('a{}'.format(i + 1) for i in range(int(sys.argv[1]))))

Executed with the no. of your functions (python generate_funcs.py 100500), would produce a file called funcs.inc with:

a1,
a2,
...
a100500

You can then include it in your C code:

int (*pfunc[])(int, int) = {
#include "funcs.inc"
}

answered May 24, 2019 at 3:57

Aviv Goll

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1 Comment

tenghiz Over a year ago

Thank you for your answer. Actually, I was sincerely persuaded that this is a trivial problem and I was just lacking a deeper knowledge of the language in order to implement my wish in a couple of lines of code. Your answer suggests that the solution must be different if I work on Windows platform. Heavens...

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