Malloc breaks function-CodePudding

I have a problem where my malloc breaks my program. Removing it will make it work but I need it furter on. Can someone please explain what i'm doing wrong. Thanks in advance!!

I have this function in my graph.c

bool graph_initialise(graph_t *graph, unsigned vertex_count)
    {
      assert(graph != NULL);
        graph = (struct graph_s*) malloc(sizeof(struct graph_s));
        if (graph == NULL){return true;}
        graph->vertex_count = vertex_count;

        graph->adjacency_lists = (struct adjacency_list_s*) malloc(vertex_count * sizeof(struct adjacency_list_s));
        if (graph->adjacency_lists == NULL){
        return true;
        }

        int i;
        for (i = 1; i < vertex_count;   i){
        graph->adjacency_lists[i].first = NULL;
        }
      return false;

and this in my graph.h

typedef struct edge_s
{
  /* Points to the next edge when this edge is part of a linked list. */
  struct edge_s *next;

  unsigned tail;    /* The tail of this edge. */
  unsigned head;    /* The head of this edge. */
  unsigned weight;  /* The weight of this edge. */
} edge_t;

typedef struct adjacency_list_s
{
  edge_t *first; /* Pointer to the first element of the adjacency list */
} adjacency_list_t;

/* Type representing a graph */
typedef struct graph_s
{
  unsigned vertex_count; /* Number of vertices in this graph. */
  unsigned edge_count;   /* Number of edges in this graph. */

  /* Pointer to the first element of an array of adjacency lists. The array
   * is indexed by vertex number
   */
  adjacency_list_t *adjacency_lists;
} graph_t;

CodePudding user response：

I suspect this issue is that you are expecting this function to allocate grph for you then operating on the allocated graph from the calling code (you dont show the calling code)

ie you are doing something like

graph *gptr;
graph_initialise(gptr,42);
printf("vc = %d", gptr->vertex_count);

trouble is that grpah_initialize doesnt set gptr. You need instead

bool graph_initialise(graph_t **gptr, unsigned vertex_count)
    {
        *gptr = (struct graph_s*) malloc(sizeof(struct graph_s));
        graph_t *graph = *gptr;
        if (graph == NULL){return true;}
        graph->vertex_count = vertex_count;

        graph->adjacency_lists = (struct adjacency_list_s*) malloc(vertex_count * sizeof(struct adjacency_list_s));
        if (graph->adjacency_lists == NULL){
        return true;
        }

        int i;
        for (i = 1; i < vertex_count;   i){
        graph->adjacency_lists[i].first = NULL;
        }
      return false;

and call it like this

graph *gptr;
graph_initialise(&gptr,42);
printf("vc = %d", gptr->vertex_count);

also that for loop should probably start at 0 not 1