Thread: Array of pointers to a struct

I am working on an assignment identical to another post from a couple years ago, for reference here is the thread:

array of pointers to structures sorting addresses by zip code

They way it is written on that thread is almost identical to the way the teacher implied to have it done (only wrote part of the input block) and that thread helped me understand a lot more what was actually going on. But I am having an error:

When it gets to the output section it outputs then next name along with the zip code... I tried strncpy and strxfrm but both cause more problems than they did help.

The last part of the project is to have the output put out in order of least zip code to most zip code (00000<99999), so this is causing me a real problem and I do not see what exactly is making this happen.

Here is my code (we dont HAVE to use gets but professor suggested using it for this assignment, next lab is to rewrite this using files and fgets rather than I/O redirection):

header.h

Code:

#ifndef lab_6b_7b_Header_h
#define lab_6b_7b_Header_h

//header file intiating other headers
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

typedef struct{
    char name[25];
    char street[25];
    char state[25];
    char zip[5];
}INFORMATION;

typedef INFORMATION *INFOPTR;

//function prototypes
void INPUT(INFORMATION *work[], int *);
void OUTPUT(INFORMATION *work[], int *);

#endif

main.c

Code:

#include "header.h"

int main(void)
{
    //Intiate program
    int count=0;
    INFORMATION *work[50];

    //call input function
    INPUT(work, &count);
    
    //sort files
    //call function
    
    //call output function
    OUTPUT(work, &count);
    
    //end program
    return 0;
}

input.c

Code:

#include "header.h"

void INPUT(INFORMATION *work[], int *count)
{
    //initiate struct pointer and a blank sting for reading position]
    char location[25];
    *count=0;
    INFOPTR INFO;

    //while loop to get persons information and move it into a malloc array via pointers
    while ((gets(location)!=NULL)&&(*count<50)) {
        INFO=(INFOPTR)malloc(sizeof(INFORMATION));
        strcpy(INFO->name,location);
        getchar();
        gets(INFO->street);
        getchar();
        gets(INFO->state);
        getchar();
        gets(INFO->zip);
        getchar();
        //counter for array position
        work[(*count)++]=INFO;
    }
    return;
}

output.c

Code:

#include "header.h"

void OUTPUT(INFORMATION *work[], int *count)
{
    int i=0;
    for (i=0;i<(*count);i++) {
        printf("%s\n%s\n%s\n%s\n", work[i]->name, work[i]->street, work[i]->state, work[i]->zip);
    }
}

And here is my input:

A1, A2
20294 Lorenzana Dr
Woodland Hills, CA
91364
B1, B2
19831 Henshaw St
Culver City, CA
94023
C1, C2
5142 Dumont Pl
Azusa, CA
91112
D1, D2
20636 De Forest St
Woodland Hills, CA
91364
A1, A2
20294 Lorenzana Dr
Woodland Hills, CA
91364
E1, E2
4851 Poe Ave
Woodland Hills, CA
91364
F1, F2
20225 Lorenzana Dr
Los Angeles, CA
91111
G1, G2
20253 Lorenzana Dr
Los Angeles, CA
90005
H1, H2
5241 Del Moreno Dr
Los Angeles, CA
91110
I1, I2
5332 Felice Pl
Stevenson Ranch, CA
94135
J1, J2
5135 Quakertown Ave
Thousand Oaks, CA
91362
K1, K2
720 Eucalyptus Ave 105
Inglewood, CA
89030
L1, L2
5021 Dumont Pl
Woodland Hills, CA
91364
M1, M2
4819 Quedo Pl
Westlake Village, CA
91362
I1, I2
5332 Felice Pl
Stevenson Ranch, CA
94135
I1, I2
5332 Felice Pl
Stevenson Ranch, CA
94135
N1, N2
20044 Wells Dr
Beverly Hills, CA
90210
O1, O2
7659 Mckinley Ave
Los Angeles, CA
90001

And here is what I get back:

A1, A2
20294 Lorenzana Dr
Woodland Hills, CA
91364B1, B2
B1, B2
19831 Henshaw St
Culver City, CA
94023C1, C2
C1, C2
5142 Dumont Pl
Azusa, CA
91112D1, D2
D1, D2
20636 De Forest St
Woodland Hills, CA
91364A1, A2
A1, A2
20294 Lorenzana Dr
Woodland Hills, CA
91364E1, E2
E1, E2
4851 Poe Ave
Woodland Hills, CA
91364F1, F2
F1, F2
20225 Lorenzana Dr
Los Angeles, CA
91111G1, G2
G1, G2
20253 Lorenzana Dr
Los Angeles, CA
90005H1, H2
H1, H2
5241 Del Moreno Dr
Los Angeles, CA
91110I1, I2
I1, I2
5332 Felice Pl
Stevenson Ranch, CA
94135J1, J2
J1, J2
5135 Quakertown Ave
Thousand Oaks, CA
91362K1, K2
K1, K2
720 Eucalyptus Ave 105
Inglewood, CA
89030L1, L2
L1, L2
5021 Dumont Pl
Woodland Hills, CA
91364M1, M2
M1, M2
4819 Quedo Pl
Westlake Village, CA
91362I1, I2
I1, I2
5332 Felice Pl
Stevenson Ranch, CA
94135I1, I2
I1, I2
5332 Felice Pl
Stevenson Ranch, CA
94135N1, N2
N1, N2
20044 Wells Dr
Beverly Hills, CA
90210O1, O2
O1, O2
7659 Mckinley Ave
Los Angeles, CA
90001

I have not started the sorting code because I cannot get past this, but once I have proper zip codes I am sure I can make a sort function no problem.

I am using xcode with some breaks to read variables as various points and do not notice anything wrong until it makes it to the output functions, although this page briefly pops up between input and output functions when the breaks are up:



Any help will be much appreciated...

Originally Posted by Salem

Creating typedef's for just a pointer seldom adds any clarity to the code. Also by convention, uppercase names are used for #defines only

This is common in the case of microsoft and windows, (especially when "Hungarian" style was popular), as seen in this example from windows.h:

Code:

typedef struct _FILETIME {
    DWORD dwLowDateTime;
    DWORD dwHighDateTime;
} FILETIME, *PFILETIME, *LPFILETIME;

If this is for a class, I would recommend using the coding style preferred by the instructor. If this is just for yourself, then it doesn't matter.

Originally Posted by rcgldr

If this is just for yourself, then it doesn't matter.

Originally Posted by grumpy

That is only true if you're willing to accept the possibility of causing yourself confusion in future when you read your own code.

I seriously doubt that whether or not typedefs are in upper or lower case is going to cause confusion. There are already inconsistencies depending on the environment, for example, BYTE and DWORD in upper case while size_t is in lower case. Most Windows functions are mixed case, like CreateFile(), ... while std stuff is lower case, printf(), vector, ... .

Originally Posted by Salem

Code:

typedef struct{
    char name[25];
    char street[25];
    char state[25];
    char zip[5];
}INFORMATION;

The first thing to realise is that if you have a 5 character string like "12345", is that you need 6 characters (say your ZIP code) to store it as a string.
All C-strings are followed by a \0 character to mark the end of the string.

Of course! I, for some reason, convinced myself zip[5] would give me 0,1,2,3,4,5 but to get that I need to put [6], this was causing he next malloc to overwrite the NULL at the end of zip with the name of the next struct so without the NULL i was getting all the information until the next NULL (the one at the end of name). I cant believe I over looked this. Still learning...

Originally Posted by Salem

> typedef INFORMATION *INFOPTR;
Creating typedef's for just a pointer seldom adds any clarity to the code.
The only useful exception is typedefs for function pointers.

Professor wants us to throw a typedef in there -_-

Originally Posted by Salem

Also by convention, uppercase names are used for #defines only, such as
#ifndef LAB_HEADER_H
#define LAB_HEADER_H

I typically make a habit of trying to make functions and such all capitals to see easier..
If you mean what you quoted specifically that is there by default in xcode (macs ) so I did not even write it.
I will keep that in mind though!

Originally Posted by Salem

> INFO=(INFOPTR)malloc(sizeof(INFORMATION));
If you're compiling this as a C program, there is no need to cast the return result of malloc.
There is no positive benefit to the cast, but there is one bug made hard to find by having the cast (which would be obvious without the cast).
See the FAQ for more details.

Will reference the FAQ and such and start reading around the site, I just found this place working on this assignment, I am behind on it (due next week) and kinda rushing thus probably not thinking so clearly (see array mistake at top lol). The malloc was a direct copy of how it was explained in class and it is working so I will probably leave it for the assignment.


Thank you so much for your help even though it was something so simple. And thanks to everyone discussing uppercase vs lower case too. Im gonna go write my swap function now. Will post it on here I guess to show I am not just trying to mooch information off everyone, heh...

I think the actual swap is ok, because C is designed to let you assign to struct types like that. The problem is probably the comparison, since zip is a string, it needs to be compared lexicographically, which < and other relational operators don't do. They compare by address instead. You will have to call strcmp() or some other function to do the comparison.