How to fill in values in struct using a function?

Question

I want to call a function to fill in the values of a struct in C. I have the following code but I get errors like [Error] request for member 'id' in something not a structure or union.

#include <stdio.h> 

typedef struct {
    int       id;
    float    grades[3];
} student_t;

void scan_student (student_t *s) {
    printf("Please give student's info:\n");
    scanf("%d%f%f%f", s.id, s.grades[0], s.grades[1], s.grades[2]);
}

int main () 
{ 
    student_t stu2;

    scan_student(&stu2);

    printf("Student's info are:\n");
    printf("%6d %5.2f %5.2f %5.2f\n", stu2.id, stu2.grades[0], stu2.grades[1], stu2.grades[2]);

    return 0; 
}

And... you should have tons of warnings here. The rule says: warnings are not to be ignored (at least unless you understand why the warning and why you can ignore it in that special use case) — Serge Ballesta
– Serge Ballesta, Commented Nov 15, 2018 at 13:37
Another thing is... use English, at least English identifiers (if your audience really does not know "grade"). As you realize right here, this is a global world. In modern languages like C# I suppose you could even use Greek identifiers, and certainly Greek strings (this web application allows me to write βαθμός) -- don't do that. Stick to 7 bit ASCII, English and 80 character lines unless there is a compelling reason not to. — Peter - Reinstate Monica
– Peter - Reinstate Monica, Commented Nov 15, 2018 at 14:44
@PeterA.Schneider Yes, you are absolutely right! I'm sorry. I fixed the text. — zinon
– zinon, Commented Nov 16, 2018 at 9:20

melpomene · Accepted Answer · 2018-11-15 13:33:21Z

9

s is a pointer, not a struct. That means you can't use . on it.

Instead you have to write (*s).id (dereference, then access struct member) or s->id (same thing, but shorter).

Also, scanf %d takes a pointer, so that should be &s->id, etc.

answered Nov 15, 2018 at 13:33

melpomene

86.2k8 gold badges96 silver badges155 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

zinon · Accepted Answer · 2018-11-16 09:21:48Z

0

I also post an example without using pointers:

#include <stdio.h> 

typedef struct {
    int       id;
    float    grades[3];
} student_t;

student_t scan_student () {
    student_t s;
    printf("Please give patient's info:\n");
    scanf("%d%f%f%f", &s.id, &s.grades[0], &s.grades[1], &s.grades[2]);
    return s;
}

int main () 
{ 
    student_t stu2;

    stu2= scan_student();

    printf("Student's info are:\n");
    printf("%6d %5.2f %5.2f %5.2f\n", stu2.id, stu2.grades[0], stu2.grades[1], stu2.grades[2]);

    return 0; 
}

edited Nov 16, 2018 at 9:21

answered Nov 15, 2018 at 13:48

zinon

4,70417 gold badges77 silver badges125 bronze badges

3 Comments

Fiddling Bits Over a year ago

Passing stu2 to scan_student as an argument is pointless in your example.

Peter - Reinstate Monica Over a year ago

@FiddlingBits Has a good point. You can as well return a local variable (note: by value! returning pointers to locals is, of course, wrong); no need to pass anything as a parameter to the function. The way it is now means the following: (1) Create a local copy of the parameter (note: this is why you could as well use a local variable right away); (2) fill that; (3) return a temporary copy of the local variable on the stack; (3) copy that temporary back into stu2, overwriting whatever uninitialized values were present there.

Peter - Reinstate Monica Over a year ago

I realize that I have two third steps in my above comment ;-). Oh well.

Collectives™ on Stack Overflow

How to fill in values in struct using a function?

2 Answers 2

Comments

3 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

3 Comments

Your Answer

Sign up or log in

Post as a guest

Related