Pass two structs to the same function in C

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Hi, I wanted to know how I can pass two structs to the same function. I'm getting an error

error: incompatible type for argument 1 of fun

if I use two structs as the same type.
Here is the code

What I have tried:

typedef struct First            		
   {
    //members
    ....
   }first;

void fun( first f[size] ){
// some computation on str1 and I want to applay same computation on str2
 ....
 for(i=0;i<3;i++){
    f[i].member +=5;
 }
} 
void cal(first str1[4],first str2[4] ){
// some calculation on str1
for(i=0;iNsomesize;i++){
str2[i].member=str1[i].member;
}
fun(str2[4]);

}

 void main(){
first str1[4]; 
first str2[4];
fun(str1); // I call just str1 because firstly I want to applay fun computation on 
              //str1
}

Posted 10-May-18 0:56am

Lilyanaa

Updated 10-May-18 10:43am

v4

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2 solutions

Solution 1

Firstly, str1 is not a first, it's an array of first objects:

C++

first str1[4];

So your method definition has to match that, as it does with cal.
But there are problems here, as str2 is an array of 4 first objects, so this:

C++

str2[0].member=fun(str2[4]);

Tries to access a fifth element of teh array - C indexes start at zero, remember.
If you are trying to pass a single instance of first to fun, then declare it as

C++

void fun(first f) {
...
}

And call it with an element form one of your arrays:

C++

fun(str1[0]);
fun(str1[1]);
fun(str1[2]);
fun(str1[3]);
fun(str2[0]);
fun(str2[1]);
fun(str2[2]);
fun(str2[3]);

If you want to pass an array of first objects:

C++

void fun(first f[]) {
...
}

And pass it the array:

C++

fun(str1);
fun(str2);

But either way, this won't work:

C++

str2[0].member=fun(str2[4]);

Because fun is a void function - iut cannot return a value, so it can;t be used on the right of an equals sign.

I think you need to sit down and re-read your course notes: you appear to be a little confused as to what you are trying to do here.

Posted 10-May-18 1:22am

OriginalGriff

Comments

Lilyanaa 10-May-18 16:34pm

thanks for your notes, can you see my update please, I do something like that, but the error same incompatible type for argument 1 of fun

OriginalGriff 11-May-18 1:56am

Make your mind up!

fun(str2[4]);
...
fun(str1);

Since str1 and str2 are declared the same way ...

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CPallini · Accepted Answer · 2018-05-10T01:30:00

You need pointers. Let's try a simple example

C

#include <stdio.h>

typedef struct
{
  int x, y;
} Point;

void doubleIt( Point * p )
{
  p->x = p->x * 2;
  p->y = p->y * 2;
}

void printIt( const Point * p)
{
  printf("{%d, %d}\n", p->x, p->y);
}

int main()
{
  Point p1, p2;
  Point pa[4];
  int n;

  p1.x = 1;
  p1.y = 1;

  p2.x = 0;
  p2.y = 2;

  // accessing p1
  printIt( &p1);
  doubleIt(&p1);
  printIt( &p1);

  // accessing p2
  printIt( &p2);
  doubleIt(&p2);
  printIt( &p1);

  // accessing the pa array
  for (n = 0; n<4; ++n)
  {
    pa[n].x = n;
    pa[n].y = -n;
    printIt(&pa[n]);
    doubleIt(&pa[n]);
    printIt(&pa[n]);
  }
}