c - 数组到C程序中的指针问题

Question

这是我正在处理的程序。

void primMST(int graph[N][N])
{
     int parent[N] ; // Array to store constructed MST
     int key[N];   // Key values used to pick minimum weight edge in cut
     bool mstSet[N];  // To represent set of vertices not yet included in MST
     int i, count, v;

     // Initialize all keys as INFINITE
     for (i = 0; i < N; i++)
        key[i] = INT_MAX, mstSet[i] = false;

     // Always include first 1st vertex in MST.
     key[0] = 0;     // Make key 0 so that this vertex is picked as first vertex
     parent[0] = -1; // First node is always root of MST 

     // The MST will have N vertices
     for (count = 0; count < N-1; count++)
     {
        // Pick thd minimum key vertex from the set of vertices
        // not yet included in MST
        int u = minKey(key, mstSet);

        // Add the picked vertex to the MST Set
        mstSet[u] = true;

        // Update key value and parent index of the adjacent vertices of
        // the picked vertex. Consider only those vertices which are not yet
        // included in MST
        for (v = 0; v < N; v++)

           // graph[u][v] is non zero only for adjacent vertices of m
           // mstSet[v] is false for vertices not yet included in MST
           // Update the key only if graph[u][v] is smaller than key[v]
          if (graph[u][v] && mstSet[v] == false && graph[u][v] <  key[v])
             parent[v]  = u, key[v] = graph[u][v];
     }

     // print the constructed MST
     printMST(parent, N, graph);
}



int main()
{
    int i, j;
    int** graph = (int**) malloc(sizeof(int*)*N);
    for(i=0;i<N;i++) 
        graph[i] = (int*) malloc(sizeof(int)*N);
    FILE *fp;
    fp = fopen("AdjacencyMatrix_of_Graph_G_N.txt","r");
    char c;
    for(i=0;i<N;i++) {
        for(j = 0; j < N; j++) {
            fscanf(fp, "%c ", &c);
            graph[i][j] = c-'0';
        }
    }
    for(i=0;i<N;i++) {
        for(j=0;j<N;j++) {
            printf("%d ",graph[i][j]);
        }
        printf("\n");
    }
    primMST(graph);
    fclose(fp);
    return 0;
}

我收到以下警告。

 C:\TURBOC3\BIN\PROJECT\MST.c:125:10: warning: passing argument 1 of 'primMST' from incompatible pointer type
  primMST(graph);
          ^
C:\TURBOC3\BIN\PROJECT\MST.c:59:6: note: expected 'int (*)[30]' but argument is of type 'int **'
 void primMST(int graph[N][N])
      ^


Compilation results...
--------
- Errors: 0
- Warnings: 2
- Output Filename: C:\TURBOC3\BIN\PROJECT\MST.exe
- Output Size: 132.0068359375 KiB
- Compilation Time: 0.48s

Answer 1

正如人们在这里评论的那样，int ** 与 int[][] 不同，这就是编译器提示的原因。

我还可以看到您正在动态分配 N 数组的大小，这有两个缺点:1. malloc 是一个相当昂贵的操作，调用它 N 次似乎没有必要。2.结果不会是连续的内存块。

假设 N 是一个#define，我建议在 main() 的堆栈上分配 graph[N][N] 而不是动态分配它。