鉴于我在下面创建的结构,如何更改代码以使其从insert(student)读取而不是从现在的方式读取。基本上,目前的代码以学生的形式输入:
student guy,23
,输出结果为:
student guy (23)
到目前为止这部分工作正在进行中。插入(以及之前)代码的作用是当输入多个学生时,按字母顺序对它们进行排序 - 或者如果它们具有相同的名称,则按年龄排序。我已经完成了执行此操作的代码,但似乎无法确定如何正确调用它。
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>
#include <stdbool.h>
#include <assert.h>
#define MAX_LINE_LENGTH 80 // The longest line this program will accept
#define MAX_NUM_STUDENTS 500 // The maximum number of students this program can handle
#define MAX_NAME_SIZE 50 // The maximum allowable name length
// The declaration of the student record (or struct). Note that
// the struct contains the name as an array of characters, rather than
// containing just a pointer to the name as before.
typedef struct student_s Student;
struct student_s {
char name[MAX_NAME_SIZE];
int age;
Student* next; // Pointer to next student in a list
};
bool comesBefore(const Student* student1, const Student* student2) {
int name_compare = strcmp(student1->name, student2->name);
if (name_compare < 0) {
return true;
}
else if (name_compare == 0) {
int age1 = student1->age;
int age2 = student2->age;
if (age1 < age2) {
return true;
}
}
return false;
}
Student* insert(Student* student, Student* list) {
Student* curr = NULL;
Student* prev = NULL;
if (list == NULL)
return student;
if (comesBefore(student, list)) {
student->next = list;
return student;
}
for (curr = list, prev = NULL;
curr != NULL && comesBefore(student, curr) != true;
prev = curr, curr = curr->next);
assert(prev != NULL);
student->next = curr;
prev->next = student;
return list;
}
// Create a pool of student records to be allocated on demand
Student studentPool[MAX_NUM_STUDENTS]; // The student pool
int firstFree = 0;
// Return a pointer to a new student record from the pool, after
// filling in the provided name and age fields. Returns NULL if
// the student pool is exhausted.
Student* newStudent(const char* name, int age) {
Student* student = NULL;
if (firstFree < MAX_NUM_STUDENTS) {
student = &studentPool[firstFree];
firstFree += 1;
strncpy(student->name, name, MAX_NAME_SIZE);
student->name[MAX_NAME_SIZE - 1] = '\0'; // Make sure it's terminated
student->age = age;
student->next = NULL;
}
return student;
}
// Read a single student from a csv input file with student name in first column,
// and student age in second.
// Returns: A pointer to a Student record, or NULL if EOF or an invalid
// student record is read. Blank lines, or lines in which the name is
// longer than the provided name buffer, or there is no comma in the line
// are considered invalid.
Student* readOneStudent(FILE* file)
{
char buffer[MAX_LINE_LENGTH]; // Buffer into which we read a line from stdin
Student* student = NULL; // Pointer to a student record from the pool
// Read a line, extract name and age
char* cp = fgets(buffer, MAX_LINE_LENGTH, file);
if (cp != NULL) { // Proceed only if we read something
char* commaPos = strchr(buffer, ',');
if (commaPos != NULL && commaPos > buffer) {
int age = atoi(commaPos + 1);
*commaPos = '\0'; // null-terminate the name
student = newStudent(buffer, age);
}
}
return student;
}
// Reads a list of students from a given file. Input stops when
// a blank line is read, or an EOF occurs, or an illegal input
// line is encountered.
// Returns a pointer to the first student in the list or NULL if no
// valid student records could be read.
Student* readStudents(FILE *file)
{
Student* first = NULL; // Pointer to the first student in the list
Student* last = NULL; // Pointer to the last student in the list
Student* student = readOneStudent(file);
while (student != NULL) {
if (first == NULL) {
first = last = student; // Empty list case
}
else {
last->next = student;
last = student;
}
student= readOneStudent(file);
}
return first;
}
// printOneStudent: prints a single student, passed by value
void printOneStudent(Student student)
{
printf("%s (%d)\n", student.name, student.age);
}
// printStudents: print all students in a list of students, passed
// by reference
void printStudents(const Student* student)
{
while (student != NULL) {
printOneStudent(*student);
student = student->next;
}
}
// Main program. Read a linked list of students from a csv file, then display
// the contents of that list.
int main(void)
{
FILE* inputFile = stdin;
if (inputFile == NULL) {
fprintf(stderr, "File not found\n");
}
else {
Student* studentList = readStudents(inputFile);
printStudents(studentList);
// The program could now do various things that make use of
// the linked list, like deleting students and adding new ones,
// but the program is already quite long enough!
}
}
我认为它需要对readStudents进行某种编辑,但无论我阅读的源材料如何,都无法确定要进行的调用更改。
答案 0 :(得分:2)
关键的想法是你需要调整它:
if (first == NULL) {
first = last = student; // Empty list case
}
else {
last->next = student;
last = student;
}
目前,您正在将新学生放在列表的末尾。相反,您将按排序顺序保留列表。在概念上你有
Arthur -> Bill -> Dave
查尔斯和新纪录。所以你首先与查尔斯比较,发现查尔斯更大,所以继续比尔,然后最终击中戴夫,现在知道在比尔和戴夫之前插入查尔斯。
现在看一下insert()函数。你能看出这就是它在做什么吗?走在列表中并最终插入记录 - 注意它如何调整&#34; Bill&#34;指向新记录,并将新记录指向戴夫。