【发布时间】：2017-07-07 00:09:57
【问题描述】：
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define MAX_MODEL 25
#define MAX_LINE 50
typedef struct car{
char* model;
char* color;
int year;
struct car* next;
}car;
car* readFromFile(FILE*);
car* insertInSortedOrder(car*, char*, char*, int);
car* createCar(char*, char*, int);
void printCars(car*);
int main(int argc, char** argv){
//creating a file pointer, opening file
FILE* fptr;
fptr = fopen(*(argv+1), "r");
car* head = NULL;
//this first reads cars from files, puts it into linked list and prints
head = readFromFile(fptr);
puts("do we get here");
printCars(head);
return 0;
}
///this function reads information from a text file, sends it to insertInSortedOrder function
car* readFromFile(FILE* fptr){
char *M, *C, *year;
char *readLine= malloc(sizeof(car)*MAX_MODEL);
int yr;
car *head=NULL;
while(fgets(readLine,MAX_LINE,fptr)!= NULL){
M = strtok(readLine,"|");
C = strtok(NULL,"|");
year = strtok(NULL,"|");
yr = atoi(year);
head = insertInSortedOrder(head,M,C,yr);
}
return head;
}
//this function sends new info to createCar to put it into a list, gets it and puts it
//into sorted order according to alphabetical order by model
car* insertInSortedOrder(car* head, char* model, char* color, int year){
//if list is emppty
if(head == NULL){
head = createCar(model,color,year);
}
else{
car *new = createCar(model,color,year);
car *current,*previous;
current = head;
previous = NULL;
puts("here?");
//compares new car model to next model, if next is greater than new, move onto next pair
while(strcmp(new->model,current->model) < 0){
puts("here2");
previous = current;
current = current->next;
puts("here2.5");
}
puts("here3");
//if only one thing in the list
if(previous->next == NULL){
//new car is next on list
if(strcmp(previous->model,new->model) > 0){
previous->next = new;
}
//new car goes into top of list
else{
head = new;
head->next = previous;
}
}
//doing stuff at middle or end
//if new is greater than current
else{
puts("here4");
previous->next = new;
new->next = current;
}
}
return head;
}
//this function creates a new "node" for the list, returns pointer
car* createCar(char* model, char* color, int year){
car *newCar = malloc(sizeof(car));
newCar->color = malloc(sizeof(char)*MAX_MODEL);
newCar->model = malloc(sizeof(char)*MAX_MODEL);
strcpy(newCar->model,model);
strcpy(newCar->color,color);
newCar->year = year;
newCar->next = NULL;
return newCar;
}
//this function prints out all of things in linked list
void printCars(car* head){
if(head == NULL)
printf("List is empty\n");
else{
printf("The list of cars in inventory are:\n");
while(head!=NULL){
printf("%-5d %-25s %-13s",head->year,head->model,head->color);
printf("\n");
head = head->next;
}
}
}
该程序的目的是读入一个文件，其中包含汽车的型号名称、颜色名称和年份。读入后，将按照汽车型号升序放入链表中。这是正在读取的文件：
Tesla S|royal|2015|
GMC Yukon|white|2005|
Dodge Charger|lime|2010|
Honda Civic|cobalt|1996|
Nissan Titan|saddlewood|2008|
Chevrolet Silverado|saddlewood|1999|
Ford Focus|lime|2000|
Toyota Tacoma|gunmetal|2009|
Tesla X|black|2016|
Nissan Maxima|white|2013|
Ford Explorer|forest|1996|
Chevrolet Corvette|cherry|1982|
Tesla 3|cherry|2017|
Nissan 370Z|royal|2011|
Ford F150|cherry|2006|
Honda Accord|white|2004|
Mitsubishi Eclipse|black|2002|
Toyota Tundra|cobalt|2017|
Dodge Challenger|lemon|1970|
Chevrolet Camaro|black|1966|
将“./a.out cars.txt”放入命令提示符后，输出为
here?
here2
here2.5
Segmentation fault
由于我的 puts 语句，我知道 seg 错误发生在我的 while 循环中的“insertInSortedOrder”函数中的某处。任何有关使此功能正常工作的帮助将不胜感激，谢谢
好的，我已经将插入函数更改为：
car* insertInSortedOrder(car* head, char* model, char* color, int year){
//if list is emppty
if(head == NULL){
head = createCar(model,color,year);
}
else{
car *new = createCar(model,color,year);
car *current,*previous;
current = head;
previous = NULL;
//compares new car model to next model, if next is greater than new, move onto next pair
while( strcmp(new->model,current->model) < 0){
//if current is only node in list or end of list
if(current->next == NULL){
current->next = new;
return head;
}
else{
//move forward to compare new
previous = current;
current = current->next;
}
}
//when new is greater than current, put new on top of it
previous = new;
previous->next = current;
}
return head;
}
现在打印出来了：
The list of cars in inventory are:
2015 Tesla S royal
2005 GMC Yukon white
2010 Dodge Charger lime
1999 Chevrolet Silverado saddlewood
1982 Chevrolet Corvette cherry
1966 Chevrolet Camaro black
所以耶！没有更多的段错误，但现在我认为我只是没有好的算法
【问题讨论】：
-
1)
char *readLine= malloc(sizeof(car)*MAX_MODEL);-->char *readLine= malloc(sizeof(car)*MAX_LINE); -
2)
while(strcmp(new->model, current->model) < 0){ previous = current; current = current->next; }：在第二次循环中current是NULL。所以NULL->model发生了seg-fault。 -
还是同样的错误，我认为读取信息没有问题，因为我在 creatCar 函数中放置了一个 printf 函数来打印新节点中的数据，并将完整列表打印出来
-
您是否正在使用Valgrind 可用的平台？如果是这样，请使用它。它将非常简洁地报告您的代码在哪里滥用内存。 （请记住在启用调试的情况下进行编译。在 Unix 上，这意味着在编译到对象和链接时都使用
-g选项。）您已经确定了崩溃发生的位置。正如@BLUEPIXY 所说，您需要保护循环不访问空指针，因此while条件需要更像while (current != NULL && strcmp(new->model, current->model) < 0) { … }。崩溃通常与取消引用 NULL 相关。 -
编写代码时，尽可能独立开发新功能。在这种情况下，请先使用
int列表进行排序顺序插入，然后再尝试处理如此复杂的货物。
标签： c linked-list nodes