Graph.h
Vnode结构成员firstarc在定义时赋初值NULL，在Visual Stdio 2013下编译通过，VC6.0就不行(非静态数据成员不能初始化)

#include <stdio.h>
#include <stdlib.h>


#define MAX_VERTEX_NUM 20

typedef int InfoType, VertexType;       //在这里可以设置顶点和弧数据类型
typedef struct ArcNode
{
    int adjvex;                         //弧指向顶点的位置
    struct ArcNode *nextarc;            //指向下一条弧的指针
    InfoType *info;                     //弧相关信息的指针 例如弧长、权重等，这里用不到
}ArcNode;
typedef struct VNode
{
    VertexType data;                    //顶点信息
    ArcNode    *firstarc = NULL;        //指向第一条与该顶点相连的弧
}VNode, AdjList[MAX_VERTEX_NUM];
typedef struct
{
    AdjList vertices;                   //每个图类型中包含一个顶点数组
    int vexnum, arcnum;                 //图的顶点数和弧数
    int kind;                           //图的种类标志
}ALGraph;

void createG(ALGraph *G);
void showG(ALGraph *G);

void DFSTraverse(ALGraph G);
void DFS(ALGraph G,  int i, void(*visit) (VNode v));
inline void Print(VNode v) { printf("%d\n", v.data); }    //访问函数

Graph.cpp

#include "Graph.h"

int vnum[MAX_VERTEX_NUM] = { false };               //vnum为访问标识数组

void createG(ALGraph *G)                        //以邻接表存储方式创建图
{
    //char TemData[64]; //暂时存储顶点数据
    int i, j;                                   //函数局部变量i,j用来记录弧的顶点
    ArcNode *s;                                 //新建的弧

    printf("请输入顶点数和边数:\n");
    scanf("%d%d", &G->vexnum, &G->arcnum);

    for (int i = 0; i < G->vexnum; i++)         //输入顶点信息,这里可以用下标唯一标识每个顶点
    {
        /*scanf("%s", TemData); G->vertices[i].data = (VertexType)TemData[64];*/
        G->vertices[i].data = (VertexType)i;
    }

    for (int k = 0; k < G->arcnum; k++)
    {
        scanf("%d%d", &i, &j);

        s = (ArcNode *)malloc(sizeof(ArcNode));  //将s插入到i顶点的表头
        s->adjvex = j;
        s->nextarc = G->vertices[i].firstarc;
        G->vertices[i].firstarc = s;

        s = (ArcNode *)malloc(sizeof(ArcNode));  //将s插入到j顶点的表头
        s->adjvex = i;
        s->nextarc = G->vertices[j].firstarc;
        G->vertices[j].firstarc = s;
    }
}

void showG(ALGraph *G)                          //输出表的信息
{
    ArcNode* Tem;
    for (int i = 0; i < G->vexnum; i++)
    {
        printf("%d->", i);
        Tem = G->vertices[i].firstarc;
        while (Tem != NULL)
        {
            printf("%d->", Tem->adjvex);
            Tem = Tem->nextarc;
        }
        printf("\n");
    }
}

void DFSTraverse(ALGraph G)
{                                     
    for (int i = 0; i < G.vexnum; i++)
        if (!vnum[i]) 
            DFS(G, i, Print);
}

void DFS(ALGraph G, int i, void(*visit) (VNode v))              //对表G从顶点i开始做深度优先遍历
{
    vnum[i] = true;   visit(G.vertices[i]);
    for (ArcNode *w = G.vertices[i].firstarc; w != NULL; w = w->nextarc)
    if (!vnum[w->adjvex]) 
        DFS(G, w->adjvex, Print);
}

main.cpp

#include "Graph.h"
void main()
{
    ALGraph G;

    createG(&G);
    showG(&G);
    DFSTraverse(G);
}