Question

名为readStudents的函数应该：

读取文件顶部到正式参数条目大小（在下面的函数签名中）的条目数。条目大小是文件的第一行，它是我已经扫描的某个整数
使用大小正确的malloc创建学生类型的数组
继续从文件中读取学生条目到该学生数组中
返回指向学生数组的指针。

文件格式如下：

   Name Surname ID Grade
   Name Surname ID Grade
   ...

我执行的任务是：

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

typedef struct {
   char firstName[30], secondName[30];
   int ID;
   int grade;
} student;

student *readStudents(char *fileName, int* entry_size, int all_ids[], int* studentSize){ 
/*
all_ids is an array for counting the amount of grades per student. studentSize is the actual number of students (for example, in students1.txt it is 2)
*/
    FILE *openedFile = fopen(fileName, "r");

    if(openedFile == NULL){
       printf("A problem occured with opening of file");
       return 0;
    }

    char entrySize[10];
    fscanf(openedFile, "%[^\n]", entrySize);

    int numberOfEntries = atoi(entrySize);
    *entry_size = numberOfEntries;
    int i;
    student *students[i];
    *students = malloc(numberOfEntries * sizeof *students);
    for(i=1; !feof(openedFile); i++){
        fscanf(openedFile, "%s %s %i %i", students[i]->firstName, students[i]->secondName, 
        &(students[i]->ID), &(students[i]->grade));
    }

    return students;
}

int main(){
   int entrySize = 0;
   int allIds = 0;
   int studentSize = 0;
   student *studentsArray[entrySize];
   *studentsArray = readStudents("students1.txt", &entrySize, &allIds, &studentSize);

   int k;
   for(k=0; k<entrySize; k++){
      printf("%s %s %i %i \n", studentsArray[k]->firstName, studentsArray[k]->secondName, studentsArray[k]->ID, studentsArray[k]->grade);
   }    
}

编译并运行它后，它显示“分段错误：11”。

Answer 1

应该使用指针而不是指针数组。
malloc将为可以使用数组表示法[i]访问的结构数量分配内存。
feof通常不能很好地读取文件。而是将循环限制为分配的结构数，并确保fscanf可以读取4个项目。

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

typedef struct {
    char firstName[30], secondName[30];
    int ID;
    int grade;
} student;

student *readStudents(char *fileName, int* entry_size, int *all_ids, int* studentSize){
/*
all_ids is an array for counting the amount of grades per student. studentSize is the actual number of students (for example, in students1.txt it is 2)
*/
    FILE *openedFile = fopen(fileName, "r");

    if(openedFile == NULL){
        perror ( fileName);
        exit ( 0);
    }

    char entrySize[10];
    fscanf(openedFile, " %9[^\n]", entrySize);

    int numberOfEntries = atoi(entrySize);
    *entry_size = numberOfEntries;
    int i;
    student *students;
    if ( NULL == ( students = malloc(numberOfEntries * sizeof *students))) {
        perror ( "malloc students");
        exit ( 0);
    }
    for(i=0; i < numberOfEntries; i++){
        if ( 4 != fscanf(openedFile, "%29s %29s %d %d"
        , students[i].firstName
        , students[i].secondName
        , &students[i].ID
        , &students[i].grade)) {
            exit ( 0);
        }
    }
    fclose ( openedFile);
    return students;
}

int main(){
    int entrySize = 0;
    int allIds = 0;
    int studentSize = 0;
    student *studentsArray;
    studentsArray = readStudents("students1.txt", &entrySize, &allIds, &studentSize);

    int k;
    for(k=0; k<entrySize; k++){
        printf("%s %s %d %d \n"
        , studentsArray[k].firstName
        , studentsArray[k].secondName
        , studentsArray[k].ID
        , studentsArray[k].grade);
    }
    free ( studentArray);
}

为什么会出现错误“细分故障11”，以及如何在C中修复它？

1 个答案: