pointers, structures, and strings

Code:

---

// This is just a basic description (representation) of what I'm trying
// to do and what is happening.  I haven't programmed in C in a
// long time and I'm trying to refresh my skills.  I understand that
// things change and memory fails.  I'm using gcc 11.3 on a win10
// machine.  This file should be fully compliable.


#include <stdio.h>
#include <string.h>


struct x {
char *y;
};

#define MAX 100
struct x *z[MAX], *zz;


int main ()
{
char a[100];
int n=15;


// I'm using fgetc to read one char at a time into a[] from a datafile
// and parse as I go.


// My "sample" input:
a[0] = 'X'; a[1] = 'X'; a[2] = 'X'; a[3] = '\0';
printf("a = %s\n",a);


// So I use *zz to build the "local record" and this is where my
// problem is:


// Three main versions to do the same thing?? (only using one at
// a time):
//zz->y = &a[0];
//*zz->y = a[0]; *(++zz->y) = a[1]; *(++zz->y) = a[2]; *(++zz->y) = a[3];
strcpy(zz->y,&a[0]);


printf("zz->y = %s\n",zz->y);  // This doesn't print because I believe
                                            // the previous statements cause a
                                            // segmentation fault and the run
                                            // terminates.


// When done with building the local record, I want to assign it to
// the next location in *z[]:
z[n] = zz;
printf("z[%i]->y = %s\n",n,z[n]->y);


//I would also like to zero out *zz and a[] after every iteration.
}
// Where am I being slopy?  What changes are needed to make this
// work?  I would prefer using strcpy.
// -- Ravenhawk

---

You declare zz as a struct pointer, but don't ever initialize it.

I suggest you just declare a new instance of the struct inside your function or inside your loop, and use that as your zz value.

That appears to have worked - thank you.

Code:

---

/*
The previous code and solution has evolved into a different issue now.  When this program is run,
it produces this output:
zzz.y = Hello <> zzz.y2 = (null)
zzz.y = World - zzz.y2 = World
z[15]->y = World ->y2 = World

When I add the 'a1' variable, in place of the 2nd instance of the 'a' variable, I get this output:
zzz.y = Hello <> zzz.y2 = (null)
zzz.y = Hello - zzz.y2 = World
z[15]->y = Hello ->y2 = World

This is a pointer issue that I can't really comphrend.  I see what is happening, but I don't understand
it.  The 2nd iteration is what I am looking for but I do not want to have to use a different string
variable for each new 'word'.  I thought that strcpy made a new copy of the source, pointed to by
only destination, but it appears that destination is still pointing to source (not just a copy). 
Therefore, when 'a1' gets a new value in the second instance, .y points to it too and not the first word.

How can this be fixed?

*/
#include <stdio.h>
#include <string.h>

struct x {
char *y;
char *y2;
};

#define MAX 100
struct x *z[MAX], zzz;

int main ()
{
char a[100];
//char a1[100];
int n=15;

strcpy(a,"Hello\0");
zzz.y = &a[0];
printf("zzz.y = %s <> zzz.y2 = %s\n",zzz.y,zzz.y2);

strcpy(a,"World\0");
zzz.y2 = &a[0];
//strcpy(a1,"World\0");
//zzz.y2 = &a1[0];
printf("zzz.y = %s - zzz.y2 = %s\n",zzz.y,zzz.y2); 

z[n] = &zzz;
printf("z[%i]->y = %s ->y2 = %s\n",n,z[n]->y,z[n]->y2);


}

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What are you trying to achieve?

This, without the need to specify an array size for the struct members?

Code:

---

struct x {
    char y[10];
    char y2[20];
};
 
#define MAX 100
struct x *z[MAX];

---

> strcpy(a,"Hello\0");
There's no need to put a \0 on the end of strings, you get one for free anyway.