Passing struct to function

Question

I m a new C programmer and I wanted to know how I can pass a struct through to a function  I m getting an error and can t figure out the correct syntax to do it  Here is the code for it      Struct   struct student      char firstname 30       char surname 30       struct student person    Call   addStudent person     Prototype   void addStudent struct student     and the actual function   void addStudent person        return      Compiler errors      line 21  warning  dubious tag declaration  struct student   line 223  argument  1 is incompatible with prototype

User · Answer

When passing a struct to another function, it would usually be better to do as Donnell suggested above and pass it by reference instead.

A very good reason for this is that it makes things easier if you want to make changes that will be reflected when you return to the function that created the instance of it.

Here is an example of the simplest way to do this:

#include <stdio.h>

typedef struct student {
    int age;
} student;

void addStudent(student *s) {
    /* Here we can use the arrow operator (->) to dereference 
       the pointer and access any of it's members: */
    s->age = 10;
}

int main(void) {

    student aStudent = {0};     /* create an instance of the student struct */
    addStudent(&aStudent);      /* pass a pointer to the instance */

    printf("%d", aStudent.age);

    return 0;
}

In this example, the argument for the addStudent() function is a pointer to an instance of a student struct - student *s. In main(), we create an instance of the student struct and then pass a reference to it to our addStudent() function using the reference operator (&).

In the addStudent() function we can make use of the arrow operator (->) to dereference the pointer, and access any of it's members (functionally equivalent to: (*s).age).

Any changes that we make in the addStudent() function will be reflected when we return to main(), because the pointer gave us a reference to where in the memory the instance of the student struct is being stored. This is illustrated by the printf(), which will output "10" in this example.

Had you not passed a reference, you would actually be working with a copy of the struct you passed in to the function, meaning that any changes would not be reflected when you return to main - unless you implemented a way of passing the new version of the struct back to main or something along those lines!

Although pointers may seem off-putting at first, once you get your head around how they work and why they are so handy they become second nature, and you wonder how you ever coped without them!

User · Answer

You need to specify a type on person   void addStudent struct student person            Also  you can typedef your struct to avoid having to type struct every time you use it   typedef struct student        student t   void addStudent student t person

User · Answer

This is how to pass the struct by reference  This means that your function can access the struct outside of the function and modify its values  You do this by passing a pointer to the structure to the function    include  lt stdio h gt     card structure definition    struct card       int face     define pointer face       end structure card  typedef struct card Card       prototype    void passByReference Card  c     int main void        Card c       c face   1       Card  cptr    amp c      pointer to Card c      printf  The value of c before function passing    d n   c face       printf  The value of cptr before function    d n  cptr- gt face        passByReference cptr        printf  The value of c after function passing    d n   c face        return 0      successfully ran program    void passByReference Card  c        c- gt face   4      This is how you pass the struct by value so that your function receives a copy of the struct and cannot access the exterior structure to modify it  By exterior I mean outside the function    include  lt stdio h gt       global card structure definition    struct card       int face      define pointer face      end structure card  typedef struct card Card       function prototypes    void passByValue Card c    int main void        Card c       c face   1       printf  c face before passByValue      d n   c face        passByValue c        printf  c face after passByValue      d n  c face       printf  As you can see the value of c did not change n        printf   nand the Card c inside the function has been destroyed            n no longer in memory         void passByValue Card c        c face   5

User · Answer

The line function implementation should be   void addStudent struct student person         person is not a type but a variable  you cannot use it as the type of a function parameter   Also  make sure your struct is defined before the prototype of the function addStudent as the prototype uses it

User · Answer

Instead of    void addStudent person        return      try this   void addStudent student person        return      Since you have already declared a structure called  student  you don t necessarily have to specify so in the function implementation as in   void addStudent struct student person        return

[c] Passing struct to function

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