在C中列印結構的問題

我對此非常陌生，并且有一項學校作業，我必須撰寫一個成績簿程式，該程式使用自定義結構來保存學生 ID 和成績。幾天來我一直在嘗試不成功地弄清楚為什么它不能正確列印，或者當它列印時（經過大量轉移之后）它只列印第二組輸入。我無計可施。任何人都可以幫忙嗎？

Gradebook.h 部分是自定義結構。

// gradebook.h

struct gradeID
{
    int id;
    char grades[25];
};

// Gradebook.h is a header file to define
// a global structure.
    
#include "gradebook.h"
#include <stdio.h>
#include <stdlib.h>
    
void sort(struct gradeID *, int);
    
int main(void)
{
    // Variables and structure definitions
    int ctr;
    char contInput;
    int i;
    struct gradeID grade;
    struct gradeID *identifier;
    int *temps;
    
    // Allocates 10 integers worth of memory for the program to use.
    // If there is not enough memory, the program will print an error
    // statement and terminate the program.
    temps = (int *) malloc(10 * sizeof(int));
    if (temps == 0)
    {
        printf("Not enough memory!\n");
        exit(1);
    }
    
    // Prints basic instructions for the program
    printf("\t\tGradebook Recorder\n");
    printf("Input student IDs and grades.\n");
    printf("These will be sorted by ID and printed.\n");
    
    
    /* Creates a for loop that will continue until the program
       hits the designated number of array elements. For the sake
       of expediency, I have set this amount to 10, but it can be
       changed as necessary.*/
    for(i = 0; i < 10; i  )
    {
        printf("Input student ID:\n");
        scanf(" %d", &grade.id);
        printf("Input grade:\n");
        scanf(" %s", grade.grades);
    
        // This allows early exit of the program
        printf("Do you have more grades to enter?\n");
        printf("Y/N\n");
        scanf(" %c", &contInput);
    
        if(contInput == 'N' || contInput == 'n')
        {
            printf("Finalizing and printing input-\n\n");
            break;
        }
    
        ctr  ;
    }
    
    printf("Grades Sorted by Student ID:\n\n");
    printf("\tStudent ID: Student Grade: \n");
    
    for(i = 0; i < ctr; i  )
    {
        printf("\t%d", grade.id );
        printf("\t%s", grade.grades);
    }
    
    identifier[i] = grade;
    
    return(0);
    
    free(temps);
}
    
void sort(struct gradeID identifier[], int counter)
{
    int inner;
    int outer;
    struct gradeID temp;
    
    // Loops for sorting
    for(outer = 0; outer < counter - 1;   outer)
    {
        for(inner = outer   1; inner < counter;   inner)
        {
            if(identifier[inner].id < identifier[outer].id)
            {
                temp = identifier[inner];
                identifier[inner] = identifier[outer];
                identifier[outer] = temp;
            }
        }
    
    }
    return;
}

uj5u.com熱心網友回復：

指標identifier未初始化

struct gradeID *identifier;

所以這個說法

identifier[i] = grade;

獨立于i呼叫未定義行為的值。

在這個 for 回圈中

for(i = 0; i < 10; i  )
{
    printf("Input student ID:\n");
    scanf(" %d", &grade.id);
    printf("Input grade:\n");
    scanf(" %s", grade.grades);

    // This allows early exit of the program
    printf("Do you have more grades to enter?\n");
    printf("Y/N\n");
    scanf(" %c", &contInput);

    if(contInput == 'N' || contInput == 'n')
    {
        printf("Finalizing and printing input-\n\n");
        break;
    }

    ctr  ;
}

grade您正在結構型別的同一物件中輸入新資料。因此，新資料會覆寫物件中存盤的先前資料。

此外，變數ctr未初始化

int ctr;

所以上面for回圈中的這個陳述句

ctr  ;

還呼叫未定義的行為。

temps指向動態分配陣列的變數

temps = (int *) malloc(10 * sizeof(int));

未使用。

這個說法

free(temps);

永遠不會獲得控制權，因為在它之前有 return 陳述句

return(0);

free(temps);

您需要定義一個型別的陣列，struct gradeID例如

struct gradeID grades[10];

并用值填充它。

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