Print a struct

[arnuld]

I am unable to add anything to this struct> I can't understand why I am
getting a Segfault:



#include <stdio.h>


struct macd
{
int price;
};


void print_combo( struct macd* );


int main(void)
{
struct macd* my_combo = NULL;

my_combo->price = 100;


return 0;
}


void print_combo( struct macd* mc )
{
if( mc )
{
printf("Price = %d\n", mc->price);

}
}

 

[LoYwEnG]

I am unable to add anything to this struct> I can't understand why I am
getting a Segfault:

#include <stdio.h>

struct macd
{
  int price;

};

void print_combo( struct macd* );

int main(void)
{
  struct macd* my_combo = NULL;

Maybe because of this statement.

 

[Martien Verbruggen]

I am unable to add anything to this struct> I can't understand why I am
getting a Segfault:

struct macd
{
int price;
};

int main(void)
{
struct macd* my_combo = NULL;

This is not a struct. It's a pointer to a struct. And it doesn't point
to anywhere where there could be a struct.

my_combo->price = 100;

You're trying to dereference the pointer that you just set to NULL
yourself. You can't do that. Either allocate memory with malloc, or use
a struct.


struct macd *my_combo ;
macd = malloc(sizeof *macd);
my_combo->price = 100;

OR

struct macd my_combo;
my_combo.price = 100;

Just like any other pointer, a struct pointer needs to point to
some memory.

Martien

 

[Lew Pitcher]

I am unable to add anything to this struct> I can't understand why I am
getting a Segfault:



#include <stdio.h>


struct macd
{
int price;
};


void print_combo( struct macd* );


int main(void)
{
struct macd* my_combo = NULL;

my_combo is a pointer to a structure. The pointer is set to NULL. There is
no space allocated to the structure.

my_combo->price = 100;

Here, you put a value into the structure. Where did this value wind up?
Remember, at this point, the structure only exists in potential, and /not/
as an object that can be modified. So, what did you modify?

Remember also that my_combo is a pointer, which (at the moment) points to
(the official) nowhere. So, again, where did your value of 100 go?

return 0;
}

[snip]

--
Lew Pitcher

Master Codewright & JOAT-in-training | Registered Linux User #112576
http://pitcher.digitalfreehold.ca/ | GPG public key available by request
---------- Slackware - Because I know what I'm doing. ------

 

[santoshsy]

I am unable to add anything to this struct> I can't understand why I am
getting a Segfault:

#include <stdio.h>

struct macd
{
  int price;

};

void print_combo( struct macd* );

int main(void)
{
  struct macd* my_combo = NULL;

my_combo = malloc(sizeof(struct macd)); // Allocating Memory

This should work fine.