Assigning multidimensional array in C

Question

I'm trying to assign multidimensional array to unitilized array in struct like this:

typedef struct TestStruct
{
    int matrix[10][10];

} TestStruct;

TestStruct *Init(void)
{
    TestStruct *test = malloc(sizeof(TestStruct));

    test->matrix = {{1, 2, 3}, {4, 5, 6}};

    return test;
}

I got next error:

test.c:14:17: error: expected expression before '{' token
  test->matrix = {{1, 2, 3}, {4, 5, 6}};

What is the best way in C to assign matrix?

Arrays cannot be assigned in C. They can be initialised, but this can only be done on definition. — alk
– alk, Commented Jul 31, 2016 at 17:46

chqrlie · Accepted Answer · 2016-07-31 13:43:01Z

4

You cannot initialize the matrix this way. In C99, you can do this instead:

*test = (TestStruct){{{1, 2, 3}, {4, 5, 6}}};

Before C99, you would use a local structure:

TestStruct *Init(void) {
    static TestStruct init_value = {{{1, 2, 3}, {4, 5, 6}}};

    TestStruct *test = malloc(sizeof(TestStruct));

    if (test)
        *test = init_value;

    return test;
}

Note that structure assignent *test = init_value; is substantially equivalent to using memcpy(test, &init_value, sizeof(*test)); or a nested loop where you copy the individual elements of test->matrix.

You can also clone an existing matrix this way:

TestStruct *Clone(const TestStruct *mat) {

    TestStruct *test = malloc(sizeof(TestStruct));

    if (test)
        *test = *mat;

    return test;
}

edited Jul 31, 2016 at 13:43

answered Jul 31, 2016 at 12:06

chqrlie

152k12 gold badges145 silver badges231 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

jl284 Over a year ago

But I want initialize matrix in Init() function, is there a way to do it via pointers?

chqrlie Over a year ago

@JacobLutin: the various methods described above do initialize the matrix. What do you mean by is there a way to do it via pointers?

Collectives™ on Stack Overflow

Assigning multidimensional array in C

1 Answer 1

2 Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

2 Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related