我一直在编写一个小程序，允许用户读取文件，创建一个小的“数据库”以及创建/删除条目等的能力。当我尝试使用
realloc()
功能，它崩溃了。
我不确定我做错了什么，可能是因为我对C.很新。
所以，我尝试这样做：
StudentDB database;
//More code in between, that does include malloc()
database->students = realloc(database->students, (database->numberOfStudents + 1) * sizeof(Student));
//It crashes when it gets to that part.
我想要做的是使用realloc（）函数作为结构内部的指针。
这是到目前为止的整个程序：
#include <stdio.h>
#include <stdlib.h>
typedef struct Lesson {
char *name;
int semester;
float grade;
} Lesson;
typedef struct Student {
char *name;
char *surname;
int id;
int numberOfLessons;
Lesson *lesson;
} Student;
typedef struct Database {
int numberOfStudents;
Student *student;
} StudentDB;
static int maxNameSize = 100;
static int autoclear = 1;
void addStudent(FILE *studentFile, StudentDB *database) {
database->numberOfStudents++;
printf("\nAdded +1 to number of students");
database->student = realloc(&database->student, 10);
//
// printf("Name of the student: ");
// scanf("%s", database.student[database.numberOfStudents].name);
}
void clear() {
if(autoclear) {
system("cls");
}
}
Lesson getNextLesson(FILE *studentFile) {
Lesson lesson;
lesson.name = malloc(maxNameSize * sizeof(char));
if(!lesson.name) { printf("Memory Allocation has failed. Exiting the program!"); exit(0); }
fscanf(studentFile, "%s", lesson.name);
fscanf(studentFile, "%d", &lesson.semester);
fscanf(studentFile, "%f", &lesson.grade);
printf("\n\t%s %d || %.2f\n", lesson.name, lesson.semester, lesson.grade);
return lesson;
}
Student getNextStudent(FILE *studentFile) {
Student student;
student.name = malloc(maxNameSize * sizeof(char));
if(!student.name) { printf("Memory Allocation has failed. Exiting the program!"); exit(0); }
fscanf(studentFile, "%s", student.name);
student.surname = malloc(maxNameSize * sizeof(char));
if(!student.surname) { printf("Memory Allocation has failed. Exiting the program!"); exit(0); }
fscanf(studentFile, "%s", student.surname);
fscanf(studentFile, "%d", &student.id);
fscanf(studentFile, "%d", &student.numberOfLessons);
printf("%d || %s %s || %d\n", student.id, student.name, student.surname, student.numberOfLessons);
int lesson;
student.lesson = malloc(student.numberOfLessons * sizeof(Lesson));
for(lesson = 0; lesson < student.numberOfLessons; lesson++) {
student.lesson[lesson] = getNextLesson(studentFile);
}
return student;
}
void loadStudents() {
}
void run(FILE *studentFile, StudentDB *database) {
int answer;
do {
clear();
answer = menu();
switch(answer) {
case 1: {
break;
}
case 2: {
break;
}
case 3: {
addStudent(studentFile, &database);
break;
}
case 4: {
break;
}
}
} while(answer < 0 || answer > 9);
}
int menu() {
int answer;
printf("1. Load students records from file\n");
printf("2. Save students records to file\n");
printf("3. Add a student record\n");
printf("4. Delete a student record by student id\n");
printf("5. Display a student record by student id\n");
printf("6. Display a student record by student surname\n");
printf("7. Display all student records\n");
printf("8. Find the lesson average for all students\n");
printf("9. Exit\n");
printf("Enter the number of the thing you would like to do: ");
// scanf("%d", &answer);
return 3;
}
void programInfo() {
printf("\n\n====================================================\n\tProgram Info\n\n This program was created by KKosyfarinis\n\n [email protected]\n====================================================\n\n");
}
void readData(FILE *studentFile, StudentDB *db) {
int i;
printf("Running the loop\n");
for(i = 0; i < db->numberOfStudents; i++) {
printf("=====================\n\n\tStudent #%d\n", i);
db->student[i] = getNextStudent(studentFile);
printf("\n\tCompleted\n\n=====================\n");
}
clear();
}
void saveStudents() {
}
void main() {
system("color 02");
system("@echo off");
FILE *studentFile;
StudentDB database;
studentFile = fopen("students.txt", "r+w");
int numberOfStudents;
//Set the number of students
fscanf(studentFile, "%d", &database.numberOfStudents);
//Prints the number of students
printf("Number of students: %d\n", database.numberOfStudents);
//Set the memory allocation
database.student = malloc(database.numberOfStudents * sizeof(Student));
if(!database.student) {
printf("The memory allocation has failed. Exiting the program!");
exit(0);
}
//Read the students
readData(studentFile, &database);
programInfo();
run(studentFile, &database);
}
在此先感谢您的帮助！
这条线怎么样？
addStudent(studentFile, &database);
在run功能？指向局部变量的指针并传递给addStudent函数
void run(FILE *studentFile, StudentDB *database) {
...
case 3: {
addStudent(studentFile, &database); // <-- get pointer to local variable
我认为即使没有这种修改，尼克的改变也无法使用此代码
addStudent(studentFile, database);
你有两个代码块有不同的行。其中一个（较大的一个）是不正确的。你是否正在引用student指针？这不是必需的，只需传递指针本身即可。
database->student = realloc(&database->student, 10);
应该：
database->student = realloc(database->student, 10);
你也没有传递一个真实的大小，但你的第一个代码示例是。以下行不起作用吗？
database->students = realloc(database->students, (database->numberOfStudents + 1) * sizeof(Student));
这只是从你的问题中复制而来。我很困惑你有什么/没有尝试过，哪一个给你错误。
此外，在未来提供更多仍然产生错误的minimal example。在剥离代码的同时，你也有可能找出问题所在。