大小为 4 的无效读取

Question

你好，我有以下代码：

struct Edge
{
    Node * nodeA, * nodeB;
    int weight;
};
.
.

这是 typedef'd 以简单地 Edge 其他地方。

.
.

int cmp(const void *b, const void *a)
{
    Edge * e1 = (Edge*)a;
    Edge * e2 = (Edge*)b;
    printf(" %d++", getWeight(e1));
    printf(" %d++", getWeight(e2));
    if (getWeight(e1) != getWeight(e2))
        return (getWeight(e1) < getWeight(e2)) ? -1 : 1;
    return 0;
}

void sortEdges(Edge ** edgeList, int numEdges)
{
    qsort(edgeList, numEdges, sizeof(Edge*), cmp);
}

Valgrind 告诉我，我有一个大小为 4 的无效读取，当我输出边缘权重的值时，我得到了完全出乎意料的结果。我只能得出结论，我对 Edge* 的演员阵容有问题，或者 sizeof 在某种程度上没有按照我的想法进行。如果您需要任何信息，请告诉我。

Answer 1

有两种方法可以更正您的代码。
1.如果edgeList是(Edge *)的数组。

int cmp(const void *b, const void *a)
{
    Edge ** e1 = (Edge**)a;//notice
    Edge ** e2 = (Edge**)b;//notice
    printf(" %d++", getWeight(*e1));//notice
    printf(" %d++", getWeight(*e2));//notice
    if (getWeight(*e1) != getWeight(*e2))//notice
        return (getWeight(*e1) < getWeight(*e2)) ? -1 : 1;//notice
    return 0;
}

void sortEdges(Edge ** edgeList, int numEdges)
{
    qsort(edgeList, numEdges, sizeof(Edge*), cmp);
}

2，如果edgeList是一个Edge数组。

int cmp(const void *b, const void *a)
{
    Edge * e1 = (Edge*)a;
    Edge * e2 = (Edge*)b;
    printf(" %d++", getWeight(e1));
    printf(" %d++", getWeight(e2));
    if (getWeight(e1) != getWeight(e2))
        return (getWeight(e1) < getWeight(e2)) ? -1 : 1;
    return 0;
}

void sortEdges(Edge * edgeList, int numEdges)//notice
{
    qsort(edgeList, numEdges, sizeof(struct Edge), cmp);//notice
}