C - Access a struct variable from different functions

Question

I'm trying to declare a variable (struct typed) in a function, and manipulate it (read/write) from other functions. However, when I try to use that variable in any function that is not where I declared it, it contains only garbage.

This is my code:

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

    typedef struct
      char name[25];
      int roll;
      float marks;  
    }Student;

    void getInfo(Student student);
    void display(Student student);

    int main(int argc, char *argv[]) {
      Student student;
      getInfo(student);
      display(student);
      return 0;
    }

    void getInfo(Student student){
      printf("Enter student's name: \n");
      scanf("%s", &student.name);
      printf("Enter student's roll: \n");
      scanf("%d", &student.roll);
      printf("Enter student's grade: \n");
      scanf("%f", &student.marks);
    }

    void display(Student student){
      printf("NAME: %s\n", student.name);
      printf("ROLL: %d\n", student.roll);
      printf("GRADE: %.2f\n", student.marks);
    }

You have not initialised the struct. The copy that is passed to the input function does not change the original, and so garbage is printed. — Weather Vane
– Weather Vane, Commented Mar 3, 2019 at 17:21
Whatever book or tutorial you're reading (or class you're taking) it should have told you that function arguments in C are passed by value. That means arguments are copied, and the functions only have a local copy they work on. Modifying a copy will not change the original. Do some research about emulating pass by reference in C. — Some programmer dude
– Some programmer dude, Commented Mar 3, 2019 at 17:21

colxi · Accepted Answer · 2019-03-03 18:11:57Z

2

You should pass your struct by reference ( & operator )

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

typedef struct{
    char name[25];
    int roll;
    float marks;    
} Student;

void getInfo(Student *student);
void display(Student *student);

int main(int argc, char *argv[]) {
    Student student;
    getInfo( &student );
    display( &student );
    return 0;
}

void getInfo(Student *student){
    printf("Enter student's name:");
    scanf("%s", student->name);
    printf("Enter student's roll:");
    scanf("%d", &student->roll);
    printf("Enter student's grade:");
    scanf("%f", &student->marks);
}

void display(Student *student){
    printf("NAME: %s\n", student->name);
    printf("ROLL: %d\n", student->roll);
    printf("GRADE: %.2f\n", student->marks);
}

Demo : https://repl.it/repls/LowNonstopWeb

edited Mar 3, 2019 at 18:11

answered Mar 3, 2019 at 18:05

colxi

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