Pointers to Struct

[lewisforlife]

Here is my code:


#include <stdio.h>

typedef struct
{
int a;
} MYSTRUCTURE;

void indirect (MYSTRUCTURE *ns)
{
MYSTRUCTURE ms = *ns;

ms.a = 10;
}

int main (int argc, char *argv [])
{
MYSTRUCTURE ms;

ms.a = 5;
printf ("%d\n", ms.a);

indirect (&ms);

printf ("%d\n", ms.a);

return 0;
}

I would expect this to output:

5
10

But it instead outputs

5
5

How can I make this work how I want it. My intent was to pass the structure defined in main () to indirect () and be able to change the values of the variables indirectly.

[Zugzwang]

#include <stdio.h>

typedef struct
{
int a;
} MYSTRUCTURE;

void indirect (MYSTRUCTURE *ns)
{
ns->a = 10;
}

int main (int argc, char *argv [])
{
MYSTRUCTURE ms;

ms.a = 5;
printf ("%d\n", ms.a);

indirect (&ms);

printf ("%d\n", ms.a);

return 0;
}

The line "MYSTRUCTURE ms = *ns;" creates a copy of "*ns" and thus "ms.a = ..." only changes the value in this copy.

[lewisforlife]

The line "MYSTRUCTURE ms = *ns;" creates a copy of "*ns" and thus "ms.a = ..." only changes the value in this copy.

I see what you are saying. I have tried:


*ns->a = 10;

and I get the following when compiling:



main.c: In function 'indirect':
main.c:10 error: invlaid type argument of 'unary *' (have 'int')


How can I make this work? I want to access all of the variables in "ms" which is defined in main (). I want to change the variables by pointers in other functions. I don't want "ms" to be defined globally outside of a function. Any help is much appreciated :D

[dwhitney67]

Try


ns->a = 10;

/* OR */

(*ns).a = 10;

[lewisforlife]

Try


ns->a = 10;

/* OR */

(*ns).a = 10;


LOL, things seem so simple in hindsight. I thought I tried everything. I guess I tried everything but your solution. This worked great. Thanks! :D

[dwhitney67]

LOL, things seem so simple in hindsight. I thought I tried everything. I guess I tried everything but your solution. This worked great. Thanks! :D

You should have paid more attention to Zugzwang's post, which came before mine.

Anyhow, you are welcome.

[lewisforlife]

#include <stdio.h>

typedef struct
{
int a;
} MYSTRUCTURE;

void indirect (MYSTRUCTURE *ns)
{
ns->a = 10;
}

int main (int argc, char *argv [])
{
MYSTRUCTURE ms;

ms.a = 5;
printf ("%d\n", ms.a);

indirect (&ms);

printf ("%d\n", ms.a);

return 0;
}

The line "MYSTRUCTURE ms = *ns;" creates a copy of "*ns" and thus "ms.a = ..." only changes the value in this copy.

Thanks zugswang, I missed your solution somehow. I really appreciate the help. Thread Solved!