Initializing an array of struct in one line? (in C)

Question

I have a 2d array of structs like this,

MapStruct myMap[50][50];

So we can initialize like this,

myMap[0][0].left = 0;
myMap[0][0].up = 1;
myMap[0][0].right = 5;

I know that I can also use the below example,

MapStruct myMap[50][50] = { {0,1,5}, {2,3,7}, {9,11,8} ... };

But the problem is that there are significant empty spots in this 50x50 structure. So for example maybe from [30][40] up to [40][50] is empty and some other points here and there are empty so with the above bracket notation i have to leave empty brackets like this {},{},{} for those empty spots.

Now my question is is there a way to initialize the like below?

myMap[0][0] = {0, 1, 5}; // gives a syntax error

Saves two lines per point I'd be pretty happy with that.

Ps: I'm using the indices myMap[x][y] as keys like a dictionary object so I can't just get rid of those empty ones in the middle because that changes the indices.

Answer 1

C99 allows

myMap[0][0] = (MapStruct){0, 1, 5};

If you are restricted to C90, you can use an helper function.

mypMap[4][2] = makeStruct(3, 6, 9);

But note that

MapStruct myMap[50][50];

in a function won't initialize the array with 0 values if there are no initializer, so you'll have to use

MapStruct myMap[50][50] = {0};

And also note that one may wonder if it is wize to allocate such big arrays on the stack.

Answer 2

If you try with :

myMap[0][0] = (MapStruct) {.left = 0, .up = 1, .right = 5};

Or

myMap[0][0] = (MapStruct) {0, 1, 5};

Answer 3

如果您正在使用C99，请查找复合文字。

Answer 4

C99 allows initialization like this:

MapStruct myMap[50][50] = {
    [ 0][ 5] = { /* ... */ },
    [10][20] = { /* ... */ },
    /* ... */
};

Or, you can set up the values by assignment, like this:

MapStruct myMap[50][50];
/* ... */
myMap[ 0][ 5] = (MapStruct){ /* ... */ };
myMap[10][20] = (MapStruct){ /* ... */ };
/* ... */

Be aware that the syntax in the second method is not casting. It is notation introduced by C99 that, although it looks the same as a cast, is used to write literals of aggregate types.

Answer 5

This will give you data on the heap rather than the stack but what you want to do could be achieved with calloc from <stdlib.h> . calloc will allocate the memory space and it set initialize it to zero.

MyStruct * myMap = calloc( 50, 50 * sizeof(MyStruct));