Initialize array of structures

Question

I am having trouble initializing an array of structures in C. Here is my structure :

typedef struct Voie {
    int num;
    int sem_num[3];
    int crois[3];
} Voie;

The two arrays will contain 0, 2 or 3 integers.

I have an array of 12 "Voie" :

Voie voies[12];

And I want each of these to be initialized with these parameters :

{1,{0,16,1},{4,7,8}}
{2,{2,3},{4,5}}
{3,{},{}}
{4,{4,17,5},{7,10,11}}
{5,{6,7},{7,8}}
{6,{},{}}
{7,{8,17,9},{10,1,2}}
{8,{10,11},{10,11}}
{9,{},{}}
{10,{12,16,13},{1,4,5}}
{11,{14,15},{1,2}}
{12,{},{}}

I have tried with a function returning a structure, separating each case with a switch, but got redefinition issues. Then I found what I assume to be the best solution but still can't make it run :

int cas[][] = { {1,{0,16,1},{4,7,8}},
                    {2,{2,3},{4,5}},
                    {3,{},{}},
                    {4,{4,17,5},{7,10,11}},
                    {5,{6,7},{7,8}},
                    {6,{},{}},
                    {7,{8,17,9},{10,1,2}},
                    {8,{10,11},{10,11}},
                    {9,{},{}},
                    {10,{12,16,13},{1,4,5}},
                    {11,{14,15},{1,2}},
                    {12,{},{}}  };

for (i=0 ; i<12 ; i++) {
    voies[i] = cas[i];
}

I'm not even sure that this is possible, since the following works :

Voie v = {1,{0,16,1},{4,7,8}};

But not the following :

int tab[] = {1,{0,16,1},{4,7,8}};
Voie v = tab;

Also : how can I access to each of the elements in my structure once it is initialized ?

Thank you for your help.

This was the solution given on another post. The problem was almost the same as mine. — Scentle5S
– Scentle5S, Commented May 17, 2015 at 13:54
So many duplicates I do not know which one to use for closing this. — alk
– alk, Commented May 17, 2015 at 13:57
Sorry, I just understand what you meant. The answer I'm talking about didn't say int cas[][] but int cas[][9] but since I didn't know what the size was in my case, I let it empty. stackoverflow.com/a/22927133/4403802 — Scentle5S
– Scentle5S, Commented May 17, 2015 at 14:05

Marian · Accepted Answer · 2015-05-17 15:14:10Z

6

You can simply initialize your array with:

EDITED:

Voie voies[12] = { 
                {1,{0,16,1},{4,7,8}},
                {2,{2,3,},{4,5,}},
                {3,{0,},{0,}},
                {4,{4,17,5},{7,10,11}},
                {5,{6,7,},{7,8,}},
                {6,{0,},{0,}},
                {7,{8,17,9},{10,1,2}},
                {8,{10,11,},{10,11,}},
                {9,{0,},{0,}},
                {10,{12,16,13},{1,4,5}},
                {11,{14,15,},{1,2,}},
                {12,{0,},{0,}}  
};

edited May 17, 2015 at 15:14

answered May 17, 2015 at 13:39

Marian

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5 Comments

alk Over a year ago

It might be worth mentioning that all members/elements not being initialised explicitly in this case get initialised to 0 implicitly.

Jens Gustedt Over a year ago

It is also worth mentioning that this is not standard C. Empty {} are not allowed. (They are for C++)

user743382 Over a year ago

Which makes this answer simply wrong. There are enough C compilers out there that will flat out reject this as a syntax error. (Even if it's wrong in the question as well, it should be mentioned.)

user743382 Over a year ago

Thanks for editing, it looks good (to me, anyway) now. One thing that might be worth covering as well is what @alk hints at too: instead of {3,{0,},{0,}},, you can simply write {3}, or {3,},. But if you prefer it the way you have it now, that's fine too.

Scentle5S Over a year ago

Basically I want to do something for each element of the arrays. So currently I'm using a for loop, from 0 to 2, but if the array is empty, I don't want to do anything, and if it only contains 2 elements, I want to do something only 2 times. So I'm initializing the arrays with 3 elements anyway, which leads to some {-1,-1,-1}and {1,2,-1} and I test the value in the for loop and do stuff only if it's different from -1. What is the best way to do this ?

Marcelo Silva · Accepted Answer · 2015-05-17 13:42:30Z

2

You can access the elements like voies[5].sem_num[0].

If Im not wrong, the example value above would be 17.

answered May 17, 2015 at 13:42

Marcelo Silva

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2 Comments

Marian Over a year ago

In the original example, voies[5].sem_num[0] is zero. You probably ment voies[6].sem_num[1] which is 17.

Marcelo Silva Over a year ago

Exactly, Marian. I was just trying to see if everyone was paying attention... :P (JK, my mistake! Thanks for pointing out it!) @Scentle5S, just dont do like me did, ok?

Jens Gustedt · Accepted Answer · 2015-05-17 13:54:13Z

2

Neither your declaration cas[][] nor your initialization with empty {} is standard C.

You may have at most one empty [] in a declaration, and you'd have to put at least one 0 inside the {}.

answered May 17, 2015 at 13:54

Jens Gustedt

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