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?

Answer 1

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;
}