CODEWITHSUNDEEP
carraysreturn
hannah
hannah

Reputation: 909

Why can't I return this array?

Why am I getting the following errors?

randmst.c: In function ‘main’:

randmst.c:41: error: variable-sized object may not be initialized

randmst.c: In function ‘createGraph’:

randmst.c:84: warning: return from incompatible pointer type

randmst.c:84: warning: function returns address of local variable

createGraph() creates an array of pointers (called VertexPointer) to structs. Once it's created, I'm having trouble passing it back to main().

int main(int argc, char **argv){

    //command line arguments
    int test = atoi(argv[1]);
    int numpoints = atoi(argv[2]);
    int numtrials = atoi(argv[3]);
    int dimension = atoi(argv[4]);

    //perform trials, put results in an array
    int i;
    int trials[dimension];
    for(i = 0; i < numtrials; i++){
        VertexPointer graph[numpoint= createGraph(numpoints, dimension);

        //testing
        int y;
        int i;
        for(y = 0; y < numpoints; y++){
            for(i = 0; i < dimension; i++){
                printf("%f \n", (*graph[y]).loc[i]);
            }
            printf("\n");
        }
    }


}



//an array of pointers holding the vertices of the graph
VertexPointer
createGraph(int numpoints, int dimension){
    //seed the psuedo-random number generator
    srand(time(NULL));

    //declare an array for the vertices
    VertexPointer graph[numpoints];

    //create the vertices in the array
    int x;
    int z;
    for(x = 0; x < numpoints; x++){
        //create the vertex
        VertexPointer v;
        v = (VertexPointer)malloc(sizeof(Vertex));
        (*v).key = 100;
        //(*v).prev = 0;
        //multiple dimensions
        for(z=0; z < dimension; z++){
            (*v).loc[z] = rand_float();
        }
        //put the pointer in the array
        graph[x] = v;
    }
    return graph;
}

Upvotes: 0

Views: 132

Answers (1)

user2357112
user2357112

Reputation: 282158

C does not allow you to return arrays. Even if it did, your code declares that createGraph returns a VertexPointer, not an array of them. malloc an array of pointers, change your code to return VertexPointer *, and use a pointer instead of an array in main.

VertexPointer *
createGraph(int numpoints, int dimension) {
    ...
    VertexPointer *graph = malloc(numpoints * sizeof(*graph));
    ...
    return graph;
}

int main(int argc, char **argv) {
    ...
    VertexPointer *graph = createGraph(numpoints, dimension);
    ...
}

Upvotes: 1

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