giving an uninitialized array values in c

Question

My question is very basic, but I couldn't find anything about it. I have an array of pointers. I want to assign it like this

mat* quickAccessMatrices[6] = {&MAT_A,&MAT_B,&MAT_C,&MAT_D,&MAT_E,&MAT_F};

with MAT_A,MAT_B,...,MAT_F being variables of type mat, which is a structure defined elsewhere. this gives a warning when using -pedantic flag, saying

initializer element is not computable at load time

so I think it means I shouldn't do it.

Is there a way to do something like this:

mat* quickAccessMatrices;
quickAccessMatrices = {&MAT_A,&MAT_B,&MAT_C,&MAT_D,&MAT_E,&MAT_F};

just without it giving an error?

Or do I just need to assign it values slot by slot?

By the way, since people were asking, here is how I define mat

typedef struct mat {
        double matrix[4][4];
} mat;

I am well aware this isn't that good, but it is necessary in my case To be clear, I know that I can use normal assignment after the definition, but I'm asking if there is a better way.

How is `mat` declared? How about the variables you're using in the initializer? — dbush, May 19 '22 at 18:12
You are assigning an array to a pointer. What do you expect the result to be? Either you do it in the definition, or you need to do it at runtime later. — Marco Bonelli, May 19 '22 at 18:13
mat is a properly defined structure that works just as intended. I am not getting any errors, just warnings, and the code works fine besides them. — PlainXYZ, May 19 '22 at 18:13
Can't reproduce. Be sure to copy and paste enough code into your question to replicate the problem. — dbush, May 19 '22 at 18:18

Vlad from Moscow · Answer 1 · 2022-05-19T18:13:34.663

1

In this declaration the declared variable is a scalar object

mat* quickAccessMatrices = {&MAT_A,&MAT_B,&MAT_C,&MAT_D,&MAT_E,&MAT_F};

but you are trying to initialize it with a braced list of several initializers as an array.

You could declare an array as

mat* quickAccessMatrices[] = {&MAT_A,&MAT_B,&MAT_C,&MAT_D,&MAT_E,&MAT_F};

Or you could declare a pointer of the type mat ** and initialize it with a compound literal like

mat** quickAccessMatrices = ( mat *[] ) { &MAT_A,&MAT_B,&MAT_C,&MAT_D,&MAT_E,&MAT_F};

As for this warning

initializer element is not computable at load time

when you may not initialize arrays in file scope with non-constant expressions. So declare the array or the pointer to the compound ;literal in a function for example in main.

edited May 19 '22 at 18:13

answered May 19 '22 at 17:54

Vlad from Moscow

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I forgot to add the square brackets in the question, but I did add them in the code. the warning remains – PlainXYZ May 19 '22 at 18:11
@PlainXYZ See my appended answer. – Vlad from Moscow May 19 '22 at 18:13
I don't think I understand what "declare the array or the pointer to the compound; literal" I am already defining the array in main, and it still gives the error – PlainXYZ May 19 '22 at 18:19
@PlainXYZ You shall provide a minimal complete program that reproduces the error. – Vlad from Moscow May 19 '22 at 18:25
I'm currently trying to reproduce the issue on a smaller scale, I will need a minute – PlainXYZ May 19 '22 at 18:26
1

@PlainXYZ Maybe the error is relative to objects MAT_A and so on that also have an array as their data member and that are declared in file scope. – Vlad from Moscow May 19 '22 at 18:28
Yea, I think you're right. I'll just use the method mentioned in some other comments of assigning values after initialization. – PlainXYZ May 19 '22 at 18:31

giving an uninitialized array values in c

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