Parameterizing type definition at compile time

Question

What is a good way to define this graph data structure:

typedef struct
{
    unsigned short isExists : 1;
    WEIGHT_TYPE weight;
} Weight;

typedef struct
{
    Weight adjacencyMatrix[VERTICES_NUM][VERTICES_NUM];
    VERTEX_TYPE vertices[VERTICES_NUM];
} Graph;

using a value for VERTICES_NUM defined at compile time?

I am looking for a better solution than defining VERTICES_NUM before including the .h file that contains the above, and I do not want to use dynamic allocation.

Answer 1

I would first approach the problem with a macro that will define the types for you.

#define DEFINE_GRAPH(NAME, WEIGHT_TYPE, VERTEX_TYPE, VERTICES_NUM) \
        DEFINE_WEIGHT_TYPE(NAME, WEIGHT_TYPE); \
        DEFINE_GRAPH_TYPE(NAME, VERTEX_TYPE, VERTICES_NUM)

#define DEFINE_WEIGHT_TYPE(NAME, WEIGHT_TYPE) \
        typedef struct { \
            unsigned short isExists : 1; \
            WEIGHT_TYPE weight; \
        } WEIGHT(NAME)

#define DEFINE_GRAPH_TYPE(NAME, VERTEX_TYPE, VERTICES_NUM) \
        typedef struct { \
            WEIGHT(NAME) adjacencyMatrix[VERTICES_NUM][VERTICES_NUM]; \
            VERTEX_TYPE vertices[VERTICES_NUM]; \
        } GRAPH(NAME)

#define WEIGHT(NAME) NAME ## _Weight
#define GRAPH(NAME) NAME ## _Graph

Now, a user could do something like:

DEFINE_GRAPH(Test, char, float, 10);

And in their code, they would use the data structure like this:

int main () {
    GRAPH(Test) g;
    /* ... */
}