在函数之间传递结构

Question

I just wrote a small program to play with structures.This program works fine but i just have small doubt in one statement.Can anyone clarify me please?

#include<stdio.h>
#include<string.h>
#include<stdlib.h>
struct mystr
{
    int a;
    float b;
    char a1[10];
};
void fun(struct mystr *ptr1)
{
    struct mystr *ptr;
    ptr=malloc(sizeof(struct mystr));
    ptr->a=10;
    ptr->b=1662.3456;
    strcpy(ptr->a1,"xxxxxx");
    *ptr1=*ptr;  /* <<<<<<<<<<<- This assignment is fine? */
    free(ptr);
}
void main()
{
    struct mystr var1;
    memset(&var1,0,sizeof(struct mystr));
    fun(&var1);
    printf("my data is %4d,%10.3f,%5s\n",var1.a,var1.b,var1.a1);
}

I know that i can just pass a pointer to the fun and print it free it. But i just wanted this program to be this way(passing structure variable address and filling it). Thanks in advance.

Answer 1

This assignment

*ptr1=*ptr;  /* <<<<<<<<<<<- This assignment is fine? */

is fine. Only there is no sense to allocate dynamically one more structure that to initialize the original structure. You could write the function simpler

void fun(struct mystr *ptr1)
{
    ptr1->a = 1 0;
    ptr1->b = 1 662.3456;
    strcpy( ptr1->a1, "xxxxxx" );
}

Also instead of using memset after the structure object definition

struct mystr var1;
memset(&var1,0,sizeof(struct mystr));

you could write simply

struct mystr var1 = { 0 };

Take into account that function main in C shall be declared like

int main( void )

At least it shall have return type int.

Answer 2

in the posted code, this line:

*ptr1=*ptr;

is nonsense.

It does not copy the contents of the two structs.

to copy the contents, use memcpy( pDestination, pSource, numBytesToCopy );

IE

memcpy( ptr1, ptr, sizeof( struct mystr ) );