Question

我正在尝试从文本文件中读取信息并使用info为我的struct变量赋值。我的文本文件如下：

A 2 B C  
B 1 D NULL  
C 0 NULL NULL  
D 0 NULL NULL

我的源代码如下：

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

struct tree_node
{
    char *node_name;    
    int children_no;
    char *child_Name1;
    char *child_Name2;
};

struct tree_node nodes[4];

int main()
{
    char nodeName[10];
    int noChildren;
    char childNames1[10];
    char childNames2[10];       
    int i = 0;

    FILE *f = fopen("inputFile.txt", "r");
    if(f == NULL)
    {
        fprintf(stderr, "Can't open input file.\n");
        exit(1);
    }
    while (fscanf(f, "%s %d %s %s", nodeName, &noChildren, childNames1,childNames2) != EOF)
    {
        nodes[i].node_name = nodeName;
        nodes[i].children_no = noChildren;
        nodes[i].child_Name1 = childNames1;
        nodes[i].child_Name2 = childNames2;
        printf("Node name = %s; Number of children = %d; child 1 = %s; child 2 = %s\n", nodes[i].node_name, nodes[i].children_no, nodes[i].child_Name1, nodes[i].child_Name2);
        i = i+1;
    }

    printf("INNCORECT PRINT:\n");
    for(int j = 0; j<4; j=j+1)
    {
        printf("Node name = %s; Number of children = %d; child 1 = %s; child 2 = %s\n", nodes[j].node_name, nodes[j].children_no, nodes[j].child_Name1, nodes[j].child_Name2); 
    }
}

while循环中的printf打印正确，但是当我尝试在下面的for循环中的while循环外打印时，我的struct数组的所有4个元素似乎都是文本文件的最后一个输入。控制台输出如下：

Node name = A; Number of children = 2; child 1 = B; child 2 = C
Node name = B; Number of children = 1; child 1 = D; child 2 = NULL
Node name = C; Number of children = 0; child 1 = NULL; child 2 = NULL
Node name = D; Number of children = 0; child 1 = NULL; child 2 = NULL
INNCORECT PRINT:
Node name = D; Number of children = 2; child 1 = NULL; child 2 = NULL
Node name = D; Number of children = 1; child 1 = NULL; child 2 = NULL
Node name = D; Number of children = 0; child 1 = NULL; child 2 = NULL
Node name = D; Number of children = 0; child 1 = NULL; child 2 = NULL

对于为什么会发生这种情况的任何帮助都会非常感激，因为我已经坚持了一段时间了。如果我的问题格式错误，请提前道歉，这是我第一次在这里发帖。提前谢谢！

Answer 1

使用strdup（）

while (fscanf(f, "%s %d %s %s", nodeName, &noChildren, childNames1,childNames2) != EOF) {
    nodes[i].node_name = strdup(nodeName);
    // should check strdup() for failure since its malloc() may fail

    nodes[i].children_no = noChildren;
    nodes[i].child_Name1 = strdup(childNames1);
    nodes[i].child_Name2 = strdup(childNames2);
    printf("Node name = %s; Number of children = %d; child 1 = %s; child 2 = %s\n", nodes[i].node_name, nodes[i].children_no, nodes[i].child_Name1, nodes[i].child_Name2);
    i = i+1;
}

使用malloc（）和strcpy（）

while (fscanf(f, "%s %d %s %s", nodeName, &noChildren, childNames1,childNames2) != EOF) {
    nodes[i].node_name = malloc(strlen(nodeName) + 1);
    nodes[i].child_Name1 =  malloc(strlen(childNames1) + 1);
    nodes[i].child_Name2 =  malloc(strlen(childNames2) + 1);
    // be sure to check these for failure via == NULL

    strcpy(nodes[i].node_name, nodeName);
    nodes[i].children_no = noChildren;
    strcpy(nodes[i].child_Name1, childNames1);
    strcpy(nodes[i].child_Name2, childNames2);
    printf("Node name = %s; Number of children = %d; child 1 = %s; child 2 = %s\n", nodes[i].node_name, nodes[i].children_no, nodes[i].child_Name1, nodes[i].child_Name2);
    i = i+1;
}

在这两种情况下，完成后都应释放node_name，child_Name1和childName2的内存。

无法在C中为struct分配正确的值

1 个答案: