无法在C中为struct分配正确的值

Question

I am trying to read information off of a text file and use the info to assign values to my struct variables. My text file is as follows:

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

My source code is as follows:

#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); 
    }
}

The printf inside the while loop prints correctly, but when I try to print outside the while loop in the for loop below, it seems all 4 elements of my struct array are the last input from the text file. The console output is as follows:

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

Any help at all on why this is happening would be greatly appreciated, as I have been stuck with this for a while now. Apologies in advance if my question format is wrong, this is my first time posting here. Thanks in advance!

Answer 1

With 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;
}

With malloc() and 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;
}

In both cases, you should free the memory for node_name , child_Name1 and childName2 when you are finished with them.