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simple structure question

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Join Date: Mar 2006

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degamer106 degamer106 is offline

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simple structure question

Aug 22nd, 2006

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 C++ Syntax (Toggle Plain Text) 
#include <stdio.h>
 
struct FUN {
	char x;
	char *y;
	int z[20];
};
 
int main(void) {
 
	struct FUN fn1;
	struct FUN fn2;
	struct FUN fn3[10];
	struct FUN fn4[50];
 
return 0;
}
#include <stdio.h>

struct FUN {
	char x;
	char *y;
	int z[20];
};

int main(void) {

	struct FUN fn1;
	struct FUN fn2;
	struct FUN fn3[10];
	struct FUN fn4[50];

return 0;
}

is an assignment like fn4[23] = fn3[5] invalid?

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Join Date: May 2006

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WaltP

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Posting Sensei

Re: simple structure question

Aug 22nd, 2006

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Originally Posted by degamer106

Help with Code Tags

C++ Syntax (Toggle Plain Text)
#include <stdio.h>
 
struct FUN {
    char x;
    char *y;
    int z[20];
};
 
int main(void) {
 
    struct FUN fn1;
    struct FUN fn2;
    struct FUN fn3[10];
    struct FUN fn4[50];
 
return 0;
}
#include <stdio.h> struct FUN { char x; char *y; int z[20]; }; int main(void) { struct FUN fn1; struct FUN fn2; struct FUN fn3[10]; struct FUN fn4[50]; return 0; }
is an assignment like fn4[23] = fn3[5] invalid?

What happened when you tried it?

Set up a function to move the parts of FUN from one value to another.

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Salem

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Void main'ers are DOOMed

Re: simple structure question

Aug 22nd, 2006

> is an assignment like fn4[23] = fn3[5] invalid?
Well it's fine as far as the syntax is concerned.

However, the pointer inside the structure presents big problems.

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
fn1.y = malloc( 10 * sizeof *fn1.y );
fn2 = fn1;
free( fn1.y );
// fn2.y is now a dangling pointer.
fn1.y = malloc( 10 * sizeof *fn1.y );
fn2 = fn1;
free( fn1.y );
// fn2.y is now a dangling pointer.

Structure assignments in C know nothing about the internals of the struct, it's just a handy wrapper around
memmove( &fn2, &fn1, sizeof fn2 );

In C++, we would use a proper copy constructor to replicate what the pointer pointed to rather than just making a copy of the pointer.

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Join Date: Jul 2006

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himanjim

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Re: simple structure question

Aug 26th, 2006

structures can be copied directly into each other but copying array as such leads to error. In such cases copy the structures using pointers to the strutures.