Возвращаемое значение пропущено fscanf ошибка

That’s a nice warning, since ignoring the return value of fscanf() could lead to undefined behavior. I suppose you can’t silence that warning unless you handle the return value, that’s very easy

if (fscanf(fp, "%*d%*d%d%d%d", &z, &e, &a) == 3)
    usevalues(z, e, a);
else
    reportproblem_do_not_use_z_e_or_a();

Warnings are good teachers of how to correctly use functions, you should never ignore fscanf()‘s return value, and more importantly you should never ignore/silence a warning. If the compiler is warning about something, it must be because you are doing something wrong¹.

In this case, if you don’t check the value and proceed to use z, e or a their content might be undefined at the moment of reading them and some unexpected things will occur.

The worst part is that it will be very difficult to find out that, these unexpected things (calculations for example) are happening because you DID NOT CHECK fscanf()‘s return value.

¹_{Except in very few situations, where you intentionally do something that will trigger a warning. But those kinds of situations only happen when you are a very experienced c programmer.}

That’s a nice warning, since ignoring the return value of fscanf() could lead to undefined behavior. I suppose you can’t silence that warning unless you handle the return value, that’s very easy

if (fscanf(fp, "%*d%*d%d%d%d", &z, &e, &a) == 3)
    usevalues(z, e, a);
else
    reportproblem_do_not_use_z_e_or_a();

Warnings are good teachers of how to correctly use functions, you should never ignore fscanf()‘s return value, and more importantly you should never ignore/silence a warning. If the compiler is warning about something, it must be because you are doing something wrong¹.

In this case, if you don’t check the value and proceed to use z, e or a their content might be undefined at the moment of reading them and some unexpected things will occur.

The worst part is that it will be very difficult to find out that, these unexpected things (calculations for example) are happening because you DID NOT CHECK fscanf()‘s return value.

¹_{Except in very few situations, where you intentionally do something that will trigger a warning. But those kinds of situations only happen when you are a very experienced c programmer.}

Мне жаль, что я задаю этот вопрос (потому что в Интернете так много об этом), но я должен спросить об этом:

Упражнение включает чтение из файла со списком студентов (запись содержит: имя, фамилию и серийный номер). Я уже создал документ и состоял из 13 строк, но когда я пишу на терминале ./a.out, вывод представляет собой список из 13 строк этого типа: (null) (null) (null)

Код:

#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#define EOF (-1)
#define BUF 100

typedef struct stud{
    char *surname;
    char *name;
    char *serial;
} student;

int main(void){
    FILE *fd;
    int n = BUF;
    int k = 0;
    int i = 0;
    int ret;
    char *s = malloc(BUF * sizeof(char));
    if((fd = fopen("registry_office_students.txt","r")) == NULL){
        perror("error opening file");
        return -1;
    }
    while(fgets(s,n,fd)!=NULL){
        k++;
    }
    student *a = malloc(k*sizeof(student));
    rewind(fd);
    ret = fscanf(fd, "%s, %s, %s", a[i].surname, a[i].name, a[i].serial);
    while(fscanf(fd, "%s, %s, %s", a[i].surname, a[i].name, a[i].serial) == ret){
        i++; 
    }
    for(i=0;i<k;i++){
        printf("%s, %s, %s n", a[i].surname, a[i].name, a[i].serial);
    }
    fclose(fd);
    return 0;
}

Я снова прошу прощения и надеюсь на правильный ответ, спасибо.

The man page say:

The value EOF is returned if the end of input is reached before
either the first successful conversion or a matching failure occurs.
EOF is also returned if a read error occurs, in which case the error
indicator for the stream (see ferror(3)) is set, and errno is set to
indicate the error.

This means that you can check against EOF:

#include<stdio.h>

int main(void){
    int a;
    printf("Please give the value of A: ");

    if(scanf("%d",&a) != EOF){
        printf("nThe value of A ist%dn",a);
    }

    return 0;
}

Or:

#include<stdio.h>
#include <errno.h>
#include<string.h>

int main(void){
    int a, errnum = errno;
    printf("Please give the value of A: ");

    if(scanf("%d",&a) == EOF){
        fprintf(stderr, "Value of errno: %dn", errno);
        perror("Error printed by perror");
        fprintf(stderr, "Error opening file: %sn", strerror( errnum ));
    }

    printf("nThe value of A ist%dn",a);
    return 0;
}

This applies for:

scanf, fscanf, sscanf, vscanf, vsscanf, vfscanf — input format con‐
version