c - 我在图中添加顶点的 C 实现失败

Question

这是我的玩具程序，用于将顶点添加到图中:

#include <stdio.h>
#include <ctype.h>
#include <stdlib.h>
#include <string.h>
#include <limits.h>
typedef  struct EdgeNode{
     int adjvex;
     struct EdgeNode *nextarc;
 }ENode, *PENode;
typedef struct VertexNode{
     char *data; 
     ENode *firstarc; 
 }VNode;

typedef  struct MyGraph{
     VNode vertices[INT_MAX];

}Graph;



/**void make_node(Graph *G, char *first){
     int i = 0;
     G.vertices[i++].data = first;
     G.vertices[i].firstarc = NULL;
     while(i--){
        printf("the node is %s\n",G.vertices[i].data);
     }                                     
}**/

int main (){                                                                                        
    size_t sz1;
    char *line = NULL;
    //char line[1024];
    char make_nodes[] = "@n";
    char make_edges[] = "@e";
    char check_edges[] = "@q";
    static int  i = 0;
    int  is_make_node = 0;
    //Graph* pGraph;
    Graph* pGraph = malloc(sizeof(Graph));
    if (pGraph == NULL){
        fprintf(stderr, "Unable to allocate memory for new node\n");
        exit(1);
    }


    while(getline(&line, &sz1, stdin) > 0){
        char cmd[3],n1[65],n2[65],dummy[2];
        int num_args;
        num_args = sscanf(line,"%3s%64s%64s%2s",cmd,n1,n2,dummy);
        if (strcmp(cmd,make_nodes) == 0){
            if(num_args != 2){
                printf("error\n");
            }else{
                pGraph->vertices[i].data = n1;
                pGraph->vertices[i].firstarc = NULL;
                printf("the node is %s\n",pGraph->vertices[0].data);
                i++;
            }
        }
    }
        printf("---");
        printf("the node is %s\n",pGraph->vertices[0].data);
        printf("the node is %s\n",pGraph->vertices[1].data);
        printf("the node is %s\n",pGraph->vertices[2].data);
     return 0;
}

现在奇怪的事情发生了，我想一一添加顶点，当我运行代码时，它给出了这样的结果:

@n hey
the node is hey
@n jude
the node is jude
---
the node is jude
the node is jude
the node is (null)

@n(某物)意味着添加一个名为某物的节点，而我的预期输出应该是:

@n hey
the node is hey
@n jude
the node is jude
---
the node is hey
the node is jude
the node is (null)

有人发现问题了吗？我不知道为什么当我读取一个新顶点时，前一个顶点被新顶点“覆盖”。

Answer 1

使用pGraph->vertices[i].data = n1;，您可以让.data指向具有 block 作用域的(局部)变量，该变量的生命周期将结束一旦超出范围。因此，当您随后访问 vertices[x].data 时(即在循环之后，实际上甚至在循环中的第二次运行时，这会使第一次运行的局部变量无效)，您会得到未定义的行为。

要解决这个问题，请分配内容的副本:

pGraph->vertices[i].data = malloc(strlen(n1)+1);
strcpy(pGraph->vertices[i].data, n1);

或者简而言之(如果您的平台上可用):

pGraph->vertices[i].data = strdup(n1);