Explorations in Structs and sorting.

**jimtuv** · 06-14-2010

I couldn't help myself. I quickly skimmed over structs and was so thrilled with the idea that I had to try and incorporate this into what I have just learned about sorting. So I built a struct array and populated it with a couple records then did a swap. the first step to sorting.

I know it's a bit ugly but I will clean that up tomorrow. I just had to get my ideas down and give it a shot to see if I got the gist of structs and if I could apply that to my recent studies.

So heres the code and output.

Code:

/* 
 * File:   Structplay.c
 * Author: jim
 *
 * Created on June 14, 2010, 10:50 PM
 */

#include <stdio.h>
#include <stdlib.h>
#include <errno.h>


 typedef struct{
        int feet;
        double inches;
    }Height;

typedef struct{
    char *name;
    Height height;
    int weight;
    int age;
}personal_info;

void SwapClient(personal_info *clientA,personal_info *clientB);

int main(void) {

    personal_info client [10];
    int i;
    i = 1;

    client[0].name = "Wilson, Bob";
    client[0].height.feet = 5;
    client[0].height.inches = 10.5;
    client[0].weight = 185;
    client[0].age = 46;

    client[1].name = "Jones Shirley";
    client[1].height.feet = 5;
    client[1].height.inches = 2.25;
    client[1].weight = 121;
    client[1].age = 29;

    printf("before the swap ---------------------------\n\n");
    printf("Client:%s, height %d foot %.2f inches, weight = %d, age = %d\n",
    client[0].name, client[0].height.feet,client[0].height.inches,
    client[0].weight, client[0].age);

    printf("Client:%s, height %d foot %.2f inches, weight = %d, age = %d\n\n",
    client[1].name, client[1].height.feet,client[1].height.inches,
    client[1].weight, client[1].age);



    SwapClient(client,client+1);



    printf("after the swap ---------------------------\n\n");
    printf("Client:%s, height %d foot %.2f inches, weight = %d, age = %d\n",
    client[0].name, client[0].height.feet,client[0].height.inches,
    client[0].weight, client[0].age);

    printf("Client:%s, height %d foot %.2f inches, weight = %d, age = %d\n\n",
    client[1].name, client[1].height.feet,client[1].height.inches,
    client[1].weight, client[1].age);

    return 0;
}
void SwapClient(personal_info *clientA,personal_info *clientB){
    personal_info tempClient;  

    tempClient = *clientA;
    *clientA = *clientB;
    *clientB = tempClient;    
}
/*
 * Sample output------------------------------------

 before the swap ---------------------------

Client:Wilson, Bob, height 5 foot 10.50 inches, weight = 185, age = 46
Client:Jones Shirley, height 5 foot 2.25 inches, weight = 121, age = 29

after the swap ---------------------------

Client:Jones Shirley, height 5 foot 2.25 inches, weight = 121, age = 29
Client:Wilson, Bob, height 5 foot 10.50 inches, weight = 185, age = 46

Press [Enter] to close the terminal ...

 */

I know I shouldn't skim through a subject like structs and just start coding but I couldn't help my excitement. I will do a more thorough examination of the references in the next few days.

**zacs7** · 06-14-2010

Erm, what's your question?

Why not define a "print struct" function? You seem to be copy & pasting.

**jimtuv** · 06-15-2010

Originally Posted by zacs7

Erm, what's your question?

Why not define a "print struct" function? You seem to be copy & pasting.

I don't have a question yet other then did I do anything stupid?? I am exploring new ground here and have no place for feed back. So I hope that anyone that has experience might be kind enough to check what I have done and add there ideas and comments so that I may learn from their experience on the subject.

The lack of a print function was the ugliness I mentioned in my first post. I also need to add a way to populate the array. I am debating if I should do that from a file to learn something new or stick to what I know and just use user input.

**MK27** · 06-15-2010

Just keep in mind these:

Code:

    client[0].name = "Wilson, Bob";
    client[1].name = "Jones Shirley";

Are string literals and so cannot be modified.

You might want to look into "linked lists" soon. There's another issue here too, just a minute...

**Bayint Naung** · 06-15-2010

You might probably want to learn/master array,pointer and dynamic memory allocation,variable scope, type promotion, etc.

**MK27** · 06-15-2010

Nevermind -- this is just slightly unorthodox to my eye, but it does work:

Code:

void SwapClient(personal_info *clientA,personal_info *clientB){
    personal_info tempClient;  
    tempClient = *clientA;
    *clientA = *clientB;
    *clientB = tempClient;    
}

Maybe someone else will have an opinion about that.

Originally Posted by Bayint Naung

You might probably want to learn/master array,pointer and dynamic memory allocation,variable scope, type promotion, etc.

Yeah, I think the "orthodox" method here would involve that (allocated pointers). I think the way it is now may suffer from a lack of flexibility, but I could be wrong since I don't generally do that (I think the structs are being copied here, instead of swapping addresses. Which if that is the case, swapping addresses is definitely more efficient).

**Bayint Naung** · 06-15-2010

Also why not define init function.

Code:

void init_person(personal_info *person,char *name, Height height,int weight,int age);

init_person(&client[0],"MK27",height,140,99);   // eg usage

**MK27** · 06-15-2010

Originally Posted by Bayint Naung

Also why not define init function.

That would simplify things. Writing functions is very important -- it avoids duplication of code, improves "modularity" and keeps everything better organized.

Code that involves a lot of duplication and not enough modularity is sometimes called "spaghetti".

**jimtuv** · 06-15-2010

Originally Posted by MK27

Just keep in mind these:

Code:

    client[0].name = "Wilson, Bob";
    client[1].name = "Jones Shirley";

Are string literals and so cannot be modified.

You might want to look into "linked lists" soon. There's another issue here too, just a minute...

Yea I do understand they are string literals. I will look into linked lists today. Thanks for the heads up.

Originally Posted by Bayint Naung

You might probably want to learn/master array,pointer and dynamic memory allocation,variable scope, type promotion, etc.

I have been studying arrays and pointers and have a basic understanding of memory allocation. I understand pretty well variable scope and have studied type promotion but wouldn't call myself and expert on it.

Master array I will have to look up as I haven't studied that yet.

Originally Posted by MK27

Yeah, I think the "orthodox" method here would involve that (allocated pointers). I think the way it is now may suffer from a lack of flexibility, but I could be wrong since I don't generally do that (I think the structs are being copied here, instead of swapping addresses. Which if that is the case, swapping addresses is definitely more efficient).

LOL yep unorthodox is not surprising. I tend to want to try things out first then find the (normal) way of doing it. Might not be the best idea but it is funner for me that way.

You are right I copied the structs and I was pretty aware it wasn't going to be super efficient. Mainly I wanted to see how to copy a struct so that is why I did it that way.

Originally Posted by Bayint Naung

Also why not define init function.

Code:

void init_person(personal_info *person,char *name, Height height,int weight,int age);

init_person(&client[0],"MK27",height,140,99);   // eg usage

Again this was part of the ugliness. I just ran out of steam last night and thought it best to sleep a little before trying anything else. Not going to have a lot of time today. I cleaned up a little adding the print function. I will try to get more done tonight.

Thanks again everyone you are all so much help. I am learning much faster then I anticipated and I know I owe that to all the input I have received here.

Here is the code so far with the print function.

Code:

/* 
 * File:   Structplay.c
 * Author: jim
 *
 * Created on June 14, 2010, 10:50 PM
 */

#include <stdio.h>
#include <stdlib.h>
#include <errno.h>


typedef struct{
    int feet;
    double inches;
}Height;

typedef struct{
    char *name;
    Height height;
    int weight;
    int age;
}personal_info;

void SwapClient(personal_info *clientA,personal_info *clientB);
void PrintClients(personal_info *client,int a, int n);


int main(void) {

    personal_info client [10];
    int i;
    i = 1;

    client[0].name = "Wilson, Bob";
    client[0].height.feet = 5;
    client[0].height.inches = 10.5;
    client[0].weight = 185;
    client[0].age = 46;

    client[1].name = "Jones Shirley";
    client[1].height.feet = 5;
    client[1].height.inches = 2.25;
    client[1].weight = 121;
    client[1].age = 29;

    printf("before the swap ---------------------------\n\n");

    PrintClients(client,0,2);

    SwapClient(client,client+1);

    printf("after the swap ---------------------------\n\n");

    PrintClients(client,0,2);

    return 0;
}
/*
 * SwapClient                       swaps two client records
 * parameters:
 *      personal_info *clientA:     The first client record to swap
 *      personal_info *clientB:     The second client record to swap
 * prints:                          nothing
 * returns:                         nothing
 */
void SwapClient(personal_info *clientA,personal_info *clientB){
    personal_info tempClient;
    int i;
    i = 0;

    tempClient = *clientA;
    *clientA = *clientB;
    *clientB = tempClient;    
}
/*
 * PrintClients     prints out n number of client records
 * parameters:
 *      personal_info *client:  is the pointer to the client array
 *      int a:                  the record to begin with
 *      int n:                  the number of records to print from a
 * prints:                      client records
 * returns:                     nothing
 */
void PrintClients(personal_info *client,int a, int n){
    int i;

    for ( i = 0 ; i < n ; i++){
        printf("Client:%s, height %d foot %.2f inches, weight = %d, age = %d\n\n",
        client[a+i].name, client[a+i].height.feet,client[a+i].height.inches,
        client[a+i].weight, client[a+i].age);
    }
}

**nonoob** · 06-15-2010

Nothing wrong with copying entire structs that way. But as others have hinted at, data movement can become the slow part of the code. Once you've done the sorting algorithm you can start thinking about allocating a new array of pointers that point to the structs. Then only swap the pointers during sorting.

**jimtuv** · 06-15-2010

Originally Posted by nonoob

Nothing wrong with copying entire structs that way. But as others have hinted at, data movement can become the slow part of the code. Once you've done the sorting algorithm you can start thinking about allocating a new array of pointers that point to the structs. Then only swap the pointers during sorting.

That is brilliant! by pointing the pointers to the data then sorting the pointers by dereferencing you end up with an array of pointers that can be searched the same as you would if you had actually moved the data structure. So the idea is move only the pointer and not the data. I can see why that would be so much more efficient. Would you then set up an array of pointers for each member of the struct to allow searches by any data that would be desired such as by age, height or weight?? Once you have sorted an array of pointers and new data record and pointer were added then to place the pointer in the sorted array would be a matter of finding the place where it should go and shifting the pointers up in the array to make space. That then would require an dynamic array correct? Would that involve using calloc? Or am I completely off the wall on this I am pretty new to all this and maybe misunderstanding the concepts?

**MK27** · 06-16-2010

Originally Posted by jimtuv

That is brilliant! by pointing the pointers to the data then sorting the pointers by dereferencing you end up with an array of pointers that can be searched the same as you would if you had actually moved the data structure. So the idea is move only the pointer and not the data. I can see why that would be so much more efficient. Would you then set up an array of pointers for each member of the struct

In fact it is not very different than your existing code:

Code:

/* 
 * File:   Structplay.c
 * Author: jim
 *
 * Created on June 14, 2010, 10:50 PM
 */

#include <stdio.h>
#include <stdlib.h>
#include <errno.h>


typedef struct{
    int feet;
    double inches;
}Height;

typedef struct{
    char *name;
    Height height;
    int weight;
    int age;
}personal_info;

void SwapClient(personal_info **clientA,personal_info **clientB);
void PrintClients(personal_info **client, int n);


int main(void) {

    personal_info *client[10];
    int i;

	for (i=0;i<10;i++) {
		client[i] = malloc(sizeof(personal_info));
	/* error handling */
		if (!client[i]) {
			puts("OUT OF MEMORY!");
			return -1;
		}
	}

    i = 1;

    client[0]->name = "Wilson, Bob";
    client[0]->height.feet = 5;
    client[0]->height.inches = 10.5;
    client[0]->weight = 185;
    client[0]->age = 46;

    client[1]->name = "Jones Shirley";
    client[1]->height.feet = 5;
    client[1]->height.inches = 2.25;
    client[1]->weight = 121;
    client[1]->age = 29;

    printf("before the swap ---------------------------\n\n");

    PrintClients(client,2);

    SwapClient(&client[0],&client[1]);

    printf("after the swap ---------------------------\n\n");

    PrintClients(client,2);

	for (i=0;i<10;i++) free(client[i]);

    return 0;
}
/*
 * SwapClient                       swaps two client records
 * parameters:
 *      personal_info *clientA:     The first client record to swap
 *      personal_info *clientB:     The second client record to swap
 * prints:                          nothing
 * returns:                         nothing
 */
void SwapClient(personal_info **clientA,personal_info **clientB){
    personal_info *tempClient;
    int i;
    i = 0;

    tempClient = *clientA;
    *clientA = *clientB;
    *clientB = tempClient;    
}
/*
 * PrintClients     prints out n number of client records
 * parameters:
 *      personal_info *client:  is the pointer to the client array
 *      int a:                  the record to begin with
 *      int n:                  the number of records to print from a
 * prints:                      client records
 * returns:                     nothing
 */
void PrintClients(personal_info **client, int n){
    int i;

    for ( i = 0 ; i < n ; i++){
        printf("Client:%s, height %d foot %.2f inches, weight = %d, age = %d\n\n",
        client[i]->name, client[i]->height.feet,client[i]->height.inches,
        client[i]->weight, client[i]->age);
    }
}

I did not change any of the comments. If you want to get a look at all the differences on linux, run:

diff yourcode.c thiscode.c

Diff's pretty handy, the first time you use it notice the > vs. < arrows on the left.

Originally Posted by Elysia

You don't necessarily have to use malloc/calloc. So long as the data is still valid when you're searching, you can just have the actual data on the stack. Pointers can point anywhere - it just has to be a valid memory location.

Yes, but generally they might as well be on the heap (that is, malloc'd). Eg, in this case you would need to have two arrays to use the stack:

Code:

    personal_info client[10];   
    personal_info *clientptrs[10];
    for (i=0;i<10;i++) clientptrs[i] = client[i];

And then the swapping would be in the clientptrs array, which is kind of messy.

**Elysia** · 06-16-2010

You don't necessarily have to use malloc/calloc. So long as the data is still valid when you're searching, you can just have the actual data on the stack. Pointers can point anywhere - it just has to be a valid memory location.
You only need a pointer to the actual struct. Then you implement some semantics on how the structs are actually sorted. You would only move the pointers around, so no data is copied anyway if you use pointers to the structs only.

**Elysia** · 06-16-2010

But malloc/free are inefficient anyway. Plus they add bugs. So best avoid them if you can

**MK27** · 06-16-2010

Originally Posted by Elysia

But malloc/free are inefficient anyway. Plus they add bugs. So best avoid them if you can

Well, this is the "C" forum, Elysia, not the C++ forum, or the Fortran forum, et. al. Malloc/free are fundamental to C programming -- you are unlikely to get very far without them. They do not "add bugs" unless you use them incorrectly, which every programming command in every programming language ever could be used to "add bugs". You might as well "avoid C programming" if this is how you feel.

Vis, efficiency, I'm surprised to hear this coming from an STL advocate.

If you wanted to use one malloc/free call above instead of ten, you could implement a simple mempool. However, I'm not too sure how critical that is for the OP right now, and to do so you first need to learn and understand the basics. C is a minimalist language, for better or worse: we do not just hand everyone everything on a ready-made platter here.

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