c - 链表分段错误
问题描述
我编写的这个 LinkedList Checkbook 程序不断出现分段错误，并且不会显示我的支票日期？我一直在尝试调试，但找不到出错的地方。程序正常运行，除非它显示支票簿中的支票，它不显示用户在创建新支票时输入的日期。选择查看特定检查的选项时，程序会获取分段故障。
#include<stdio.h>
#include<stdlib.h>
/*
* The purpose of this program is to use a linked list in a C program.
* Date Created: 8 March 2020
*/
/*
* Variable to track items and clear the buffer
*/
char temp [50];
/* Check structure */
struct check {
int num;
char date[30];
char to[30];
float amount;
char descrip[30];
struct check *next;
};
/* Linked list of checks (checkbook) */
struct check *checkbook = NULL;
/* Keep track of last node, last check in the book */
struct check *last = NULL;
/* Function declarations */
void addCheck(); //Add a check to the checkbook
void deleteCheck(int chkNum); //Delete a check from the checkbook
void showCheck(struct check *thisCheck); //show the desired check
void showCheckbook(); //show the entire checkbook
void showSpecificCheck(int chkNum); //show a specific check to the user
/** FUNCTIONS **/
/* Adds a check to the checkbook */
void addCheck() {
/* Creates new node and memory for the node. */
struct check *newNode = (struct check *)malloc(sizeof(struct check));
/* Sets the number of the check */
if (last == NULL) {
newNode -> num = 1;
} else {
newNode -> num = last -> num + 1;
}
/* Get user input for the check */
printf("Enter the number of the check: ");
scanf("%d", &newNode -> num);
printf("Enter the date in dd/mm/yy format: ");
fgets(newNode -> date, 30, stdin);
/* Removes extra newline */
fgets(temp, 50, stdin);
printf("Enter the recipient: ");
fgets(newNode -> to, 30, stdin);
printf("Enter the amount in decimal form: ");
scanf("%f", &newNode -> amount);
/* Removes extra newline */
fgets(temp, 50, stdin);
printf("Enter a description: ");
fgets(newNode -> descrip, 30, stdin);
/* Print check info */
printf("--------------------\n");
printf("Check Number: %d\n", newNode -> num);
printf("Date: %s", newNode -> date);
printf("To: %s", newNode -> to);
printf("Amount: %.2f\n", newNode -> amount);
printf("Description: %s", newNode -> descrip);
printf("--------------------\n");
if (checkbook == NULL) {
checkbook = newNode;
last = newNode;
} else {
last -> next = newNode;
last = newNode;
}
}
/* Deleting a check */
void deleteCheck(int chkNum) {
struct check *temp = checkbook;
struct check *del = NULL;
if (temp == NULL) {
printf("Check %d was not found. \n", chkNum);
}
if(chkNum == 1) {
checkbook = temp -> next;
free(temp);
return;
}
for (int i = 0;i < chkNum-2;i++)
temp = temp -> next; //temp points to the n-1th node in the list
del = temp -> next; //nth node
temp -> next = del -> next; //n-1th node
free(del); //delete del
}
/* Show a specific check */
void showSpecificCheck(int chkNum) {
struct check *temp = checkbook;
struct check *del = NULL;
/* Empty list */
if (temp = NULL) {
printf("Check %d was not found. \n", chkNum);
}
/* First node */
else if (temp -> num == chkNum) {
showCheck(temp);
}
/* Other node */
else {
while (temp != NULL) {
/* Number is not in list */
if (temp -> next == NULL) {
printf("Check %d was not found. \n", chkNum);
break;
}
/* if number is found */
else {
showCheck(temp -> next);
}
}
}
}
/*
* Show Check Function
* @param the check to diplay
*/
void showCheck(struct check *thisCheck) {
printf("--------------------\n");
printf("Check #: %d\n", thisCheck -> num);
printf("Date: %s\n", thisCheck -> date);
printf("To: %s\n", thisCheck -> to);
printf("Amount: %.2f\n", thisCheck -> amount);
printf("Description: %s\n", thisCheck -> descrip);
printf("--------------------\n");
}
/*
* Show Checkbook Function
*/
void showCheckbook() {
struct check *current = checkbook;
while (current != NULL) {
showCheck(current);
current = current -> next;
}
}
/*
* Main function
*/
int main() {
/* Keeps the user choice displayed */
char choice = ' ';
/* Displays greeting */
printf("Aloha and welcome to your checkbook! Please select one of the options below: \n");
/* Continues to run program while user does not want to exit */
while ( choice != 'e') {
/* Display selection options to the user */
printf("Press 'a' to add a new check \n");
printf("Press 'v' to view your checkbook \n");
printf("Press 'c' to view a specific check \n");
printf("Press 'd' to delete a specific check \n");
printf("Press 'e' to exit the program \n\n");
printf("Enter your choice: \n");
/* Gets the user choice */
scanf("%c", &choice);
if (choice == 'a' ) {
addCheck();
}
else if (choice == 'v') {
showCheckbook();
/* Removes extra newline */
fgets(temp, 50, stdin);
}
else if (choice == 'c') {
int i;
printf("Enter the check number: \n");
scanf(" %d", &i);
showSpecificCheck(i);
/* Removes extra newline */
fgets(temp, 50, stdin);
}
else if (choice == 'd') {
int j;
printf("Enter the number of the check you want to delete: \n");
scanf(" %d", &j);
deleteCheck(j);
/* Removes extra newline */
fgets(temp, 50, stdin);
}
else if (choice == 'e') {
printf("Mahalo for using your checkbook. Have a great day!");
}
else {
printf("You must enter one of the selected options above.");
}
}
return(0);
}
解决方案
在函数showSpecificCheckIn()中，一段代码
//...
if (temp = NULL) {
^
printf("Check %d was not found. \n", chkNum)
//...
条件将始终评估为真，您需要的是
if (temp == NULL) {
^^
printf("Check %d was not found. \n", chkNum);
这将修复段错误。
日期问题是因为当您读取日期输入时，缓冲区中有一个挥之不去的'\n'字符stdin，所以fgets()会捕获它并将输入的日期留在缓冲区中，下一个fgets()等会读取，从而使您的所有读取脱轨，这就是为什么您觉得有必要使用
/* Removes extra newline */
fgets(temp, 50, stdin);
清除缓冲区。
但是，这并不能解决日期字段保持为空（即带有一个'\n'字符）的事实，以解决此问题getchar();，fgets(newNode->date, 30, stdin);然后您可以删除fgets(temp, 50, stdin);
您的日期将被正确读取，缓冲区将被清空。
除此之外，del您的函数中有一个未使用的变量deleteCheck()，您可能需要检查一下。