Error: cast to incomplete array type "int []" is not allowed

Question

I want to get the length of VA_ARGS

I used the answer of this question https://stackoverflow.com/a/2124433/7388699 but if doesn't work!

#define PIN_ARRAY_LENGTH(...) ((size_t)(sizeof((int[]){__VA_ARGS__})/sizeof(int)))

size_t c = PIN_ARRAY_LENGTH(1, 5, 7, 9);

I also tried

size_t x = sizeof((int[]){ 1, 6, 8 }) / sizeof(int);

It does not compile, I get the error: cast to incomplete array type "int []" is not allowed

This looks like an XY problem. What are you trying to achieve with this? — NathanOliver
– NathanOliver, Commented Dec 20, 2018 at 16:06
This is trying to create a compound literal, but these only exist in C99 and above, not in C++. — Quentin
– Quentin, Commented Dec 20, 2018 at 16:07
I want to pass CREATE_PIN_ARRAY(1, 6, 8) end then let it expand to new const unsigned int[]{1, 6, 8}, 3 I have problems to pass the size of the array — Tobi G
– Tobi G, Commented Dec 20, 2018 at 16:09
#define CREATE_PIN_ARRAY(...) const unsigned int something[] { __VA_ARGS__ }? Not sure what you're gaining by hiding that behind a macro though. Edit: oh, there's the array size in there too. Hold on. — Quentin
– Quentin, Commented Dec 20, 2018 at 16:10
If you want just get the length of VA_ARGS use this trick stackoverflow.com/a/2124385/10733631 — Dmytro Dadyka
– Dmytro Dadyka, Commented Dec 20, 2018 at 16:12

Quentin · Accepted Answer · 2018-12-20 16:13:46Z

1

Compound literals are out of the question, but you can create the array rvalue you need through a typedef:

using int_c_array = int[];

#define count_args(...) \
    (sizeof(int_c_array {__VA_ARGS__}) / sizeof(int))

answered Dec 20, 2018 at 16:13

Quentin

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Comments

Aconcagua · Accepted Answer · 2018-12-20 16:35:22Z

1

Variation of Quentin's answer:

#define NUM(...) (std::tuple_size<decltype(std::make_tuple(__VA_ARGS__))>::value)

This does not require an alias and works with arbitrary types:

size_t n = NUM(7, 10.12, "hello world");

answered Dec 20, 2018 at 16:35

Aconcagua

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