Question

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“Assignment from incompatible pointer type” warning

I have two structures, one which builds off the other. My hope is to use them together to create an adjacency list for a directed weighted graph.

Here are my structures:

typedef struct{
        int v;
        int edgeWeight;
        struct adjEdge * next;
}adjEdge;

typedef struct{
        int v;
        int weight;
        struct  adjEdge *adj;
}vertex;

So basically the vertex adj will be null unless there is a connection to another vertex, which is the adjEdge structures function.

My issue is that when I assign a adjEdge to the vertex structure I am getting an error:

bfs.c:75: warning: assignment from incompatible pointer type 

Here is part of the code. Look to it to see where the errors are actually being thrown

while((fscanf(fp, "%d %d %d", &u, &v, &w)) != EOF)
{
    vertexArray[u-1].v = u;


    adjEdge * newEdge;
    newEdge->v = v;
    newEdge->edgeWeight = w;
    newEdge->next = NULL;

    if(vertexArray[u-1].adj = NULL)
    {
        vertexArray[u-1].adj = newEdge; //error
    }
    else
    {
        adjEdge * traverse = vertexArray[u-1].adj; //error
        while(traverse->next != NULL)
        {
            traverse = traverse->next; //error
        }
        traverse->next = newEdge;  //error
    }
}

I thought once declared in my structures I could utilize assignments like this?

Answer 1

The problem is in the way you have defined structures. Define them as follows and get rid of the warnings.

typedef struct adjEdge_{
        int v;
        int edgeWeight;
        struct adjEdge_ * next;
}adjEdge;

typedef struct vertex_{
        int v;
        int weight;
        struct  adjEdge_ *adj;
}vertex;

Hope this helps!