CODEWITHSUNDEEP
c++arraysc++11struct
Bob
Bob

Reputation: 4970

C++: how to assign static array to a pointer inside a struct

I have C-code that I need to compile to C++ and need to minimally change it.

In C, the following works

typedef struct _type_t
{
    int a;
    int b;
    int c[];
}type_t;

type_t var = {1,2,{1,2,3}};

But in C++11, it gives the error

error: too many initializers for int [0]

But I cannot give type_t.c a constant size because it needs to work for any size array.

So I need to change the struct to 

typedef struct _type_t
    {
        int a;
        int b;
        int *c;
    }type_t;

But then I need to change 

type_t var = {1,2,{1,2,3}};

to something else because current code gives the error

error: braces around scalar initializer for type int*

Casting 3rd element to(int[]) gives error

error: taking address of temporary array

This is from micropython, parse.c:

#define DEF_RULE_NC(rule, kind, ...) static const rule_t rule_##rule = { RULE_##rule, kind, #rule, { __VA_ARGS__ } };

How do I initialize the array and assign it to type_t.c ?

Upvotes: 3

Views: 957

Answers (4)

Massimiliano Janes
Massimiliano Janes

Reputation: 5624

yet another alternative might be

    ...
    int * c;
}type_t;

type_t var = {1,2, []{ static int x[] = {1,2,3}; return x; }() };

PS: yes, I know it's crazy, but it's somewhat more respectful of OP requirements ( it can be incorporated in a dropin replacement macro as given )

Upvotes: 0

DeepakKg
DeepakKg

Reputation: 349

C++ doesn't allow this statement expression. You may use lightweight std::initialiser_list to achieve the objective

#include <initializer_list>
typedef struct _type_t
{
    int a;
    int b;
    std::initializer_list<int> c;
}type_t;

 type_t var = {1,2,{1,2,3,4}};

Upvotes: 1

user7860670
user7860670

Reputation: 37487

In order to do this you need to make your array really static:

typedef struct _type_t
{
    int   a;
    int   b;
    int * c;
}type_t;

int items[3] = {1,2,3};
type_t var = {1,2, static_cast< int * >(items)};

Upvotes: 6

Ron
Ron

Reputation: 15501

Use std::vector and aggregate initialization:

struct type_t
{
    int a;
    int b;
    std::vector<int> c;
};

int main() {
    type_t var = { 1, 2, { 1, 2, 3 } };
}

Upvotes: 7

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