无法解决 C 中队列列表的“循环”问题

Question

我正在使用指针、列表和结构。我有一个从 txt 文件中读取数据并将其保存在结构中的程序。将所有数据转换为节点后，我尝试打印列表。控制台中的输出就好像程序陷入了循环，永远只打印最后一个节点。

这是我的初始代码。我使用 initFromText() 打开 txt 文件并将每一行保存为一个节点。 在这个函数中，我调用了 enqueue()，它应该将新节点添加到列表的末尾，指向 NULL。

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

#define MAX_LINE_LENGTH 35

typedef struct temperature{
    float temperature;
    struct temperature *next;
} Temperature;

typedef struct patient{
    char name[25];
    int age;
    int room;
    Temperature *firstTemp;
    struct patient *next;
} Patient;

void initFromText(Patient **first);
void enqueue(Patient **first, Patient *newP);
void printPatients(Patient *first);

int main(){
    Patient *first = NULL;
    initFromText(&first);
    printPatients(first);
    return 0;
}

void initFromText(Patient **first){
    FILE *file = fopen("data.txt", "r");
    if (file == NULL) return;

    char line[MAX_LINE_LENGTH];
    Patient *newP = (Patient*)malloc(sizeof(Patient));
    Temperature *newT = (Temperature*)malloc(sizeof(Temperature));

    while(fgets(line, MAX_LINE_LENGTH, file)){
        char *name = strtok(line, ",");
        strcpy(newP->name, name);
        newP->age = atoi(strtok(NULL, ","));
        newP->room = atoi(strtok(NULL, ","));
        newT->temperature = atof(strtok(NULL, ","));
        newT->next = NULL;
        newP->firstTemp = newT;
        newP->next = NULL;
        enqueue(first, newP);
    }
    fclose(file);
}

void enqueue(Patient **first, Patient *newP){
    if (*first == NULL) *first = newP;
    else{
        Patient *current = *first;
        while (current->next != NULL) current = current->next;
        current->next = newP;
    }
}

void printPatients(Patient *first){
    if (first == NULL) printf("\n\n *No hay pacientes ingresados.\n");
    else{
        Patient *current = first;
        do{
            printf("\n********************");
            printf("\n  %s", current->name);
            printf("\nEdad: %d", current->age);
            printf("\nHabitacion: %d", current->room);
            printf("\nTemperaturas:");
            Temperature *currentTemp = current->firstTemp;
            do{
                printf("\n\t%.1f", currentTemp->temperature);
                currentTemp = currentTemp->next;
            }while(currentTemp != NULL);
            current = current->next;
            printf("\n********************");
        }while(current != NULL);
    }
}

在执行中，程序卡在了我提到的循环中。 我发现问题出在 enqueue() 函数中。我做了以下事情：

在 main() 中注释了 printPatients() 函数。

int main(){
    Patient *first = NULL;
    initFromText(&first);
    //printPatients(first);
    return 0;
}

注释了enqueue()函数，并在每次迭代中打印了newP的信息。每个节点都正确创建，指向 NULL。

void initFromText(Patient **first){
    FILE *file = fopen("data.txt", "r");
    if (file == NULL) return;

    char line[MAX_LINE_LENGTH];
    Patient *newP = (Patient*)malloc(sizeof(Patient));
    Temperature *newT = (Temperature*)malloc(sizeof(Temperature));

    while(fgets(line, MAX_LINE_LENGTH, file)){
        char *name = strtok(line, ",");
        strcpy(newP->name, name);
        newP->age = atoi(strtok(NULL, ","));
        newP->room = atoi(strtok(NULL, ","));
        newT->temperature = atof(strtok(NULL, ","));
        newT->next = NULL;
        newP->firstTemp = newT;
        newP->next = NULL;
        printf("\n********************");
        printf("\n  %s", newP->name);
        printf("\nEdad: %d", newP->age);
        printf("\nHabitacion: %d", newP->room);
        printf("\nTemperatura: %.1f", newP->firstTemp->temperature);
        printf("\nSiguiente: %s", newP->next->name);
        printf("\n********************");
        //enqueue(first, newP);
    }
    fclose(file);
}

然后，我在 enqueue() 函数中重复了这个过程。结果是第一个节点被正确创建，指向 null，但是随后，每个节点都指向自己（2nd->next = 2nd，3rd->next = 3rd，等等）。显然，“第一个”指针最终指向最后一个节点。这样，程序末尾的循环将永远打印最后一个节点。

void enqueue(Patient **first, Patient *newP){
    if (*first == NULL) *first = newP;
    else{
        Patient *current = *first;
        while (current->next != NULL) current = current->next;
        current->next = newP;
    }
    printf("\n********************");
    printf("\n  %s", newP->name);
    printf("\nEdad: %d", newP->age);
    printf("\nHabitacion: %d", newP->room);
    printf("\nTemperatura: %.1f", newP->firstTemp->temperature);
    printf("\nSiguiente: %s", newP->next->name);
    printf("\n********************");
}

我已经尝试了很多东西，但无法理解问题所在。

Answer 1

我只需要移动以下两行代码：

Patient *newP = (Patient*)malloc(sizeof(Patient));
Temperature *newT = (Temperature*)malloc(sizeof(Temperature));

从这里 (initFromText())

char line[MAX_LINE_LENGTH];
Patient *newP = (Patient*)malloc(sizeof(Patient));
Temperature *newT = (Temperature*)malloc(sizeof(Temperature));

while(fgets(line, MAX_LINE_LENGTH, file)){

到这里

char line[MAX_LINE_LENGTH];

while(fgets(line, MAX_LINE_LENGTH, file)){
    Patient *newP = (Patient*)malloc(sizeof(Patient));
    Temperature *newT = (Temperature*)malloc(sizeof(Temperature));

这解决了我只创建 1 个节点并递归地将数据保存在其中的事实。现在它为 txt 文件的每一行创建一个节点。