using a structure..

This may seem silly to most. I want to use a structure that is in another file. I will be the only one using this structure. This file is just a header file of structures. In my main file I have a method that I will want to stuff this structure (for simplicity let's call it names_a) with data from another structure (names_b) which is in another header file. Another method initially populates "name_b" with data. In a different method I want to then copy the contents from "names_a" back into "names_b". Both methods are located in the same file. Can someone please show me an example of how I can do this? Thanks in advance!
JK

Code:

---

struct names_a {
int number_of_names;
char name[10];
}

struct names_b {
int number_of_names;
char name[10];
}

---

Um, what's the purpose of all of this?

I am getting this data from another application. I want to read it into the first structure and then write it back out to the original structure that I received the data from. The purpose is to get the number of names and the name itself...do some stuff then write the data back out.

I'm quite confused what you're asking...

If it's how to read a structure froma (binary) file then it's somethign like this:

Code:

---

struct S
{
  ...
};

S my_struct;
std::ifstream file("SomeFile.bin");

file.read(static_cast<char*>(&my_struct), sizeof(S));

---

read a tutorial on fstream, such as this one
http://www.daniweb.com/tutorials/tutorial6542.html

I don't see why you need to do this structure shuffling deal you seem so bent on.

I'm stuffing "name_a" with data from a vector...this part I have verified is working correctly. The problem I'm having is when I go to stuff this data back into the vector (container) the data is no longer there...it's garbage.

prelude, I don't think the phrase "you seem so bent on is appropriate". I may not be presenting the real issue properly. For that I apolgize and will cease to post here in the future.

Quote:

---

I'm stuffing "name_a" with data from a vector...this part I have verified is working correctly. The problem I'm having is when I go to stuff this data back into the vector (container) the data is no longer there...it's garbage.

---

If you showed us some code we could help.

Quote:

---

prelude, I don't think the phrase "you seem so bent on is appropriate". I may not be presenting the real issue properly. For that I apolgize and will cease to post here in the future.

---

There's no need to cease posting entirely, just try to keep you questions specific and to the point.

A block of code is worth a thousand words :D I really can't make out what you're trying to do. Apparently you're getting this data from another application, from a file, and from a vector all at the same time. And the purpose of the code is just as unclear (to count names? of what? huuuh? :confused: ). I believe what Prelude was trying to say is judging from the information you've given us, it doesn't sound like you need to do all this structure shuffling at all - but since you haven't told us enough for us to figure out what the heck is going on, there's no way for us to know.

OK, I sincerely apologize for not providing more (clearer description and code). I am getting the data from a vector and putting it in a local struct. I'm then inanother procedure putting this data from the local struct back into the vector. I can't post the specific code due to proprietary rights. I only was asking for someone to post an example of how this could be accomplished. I only provided the two structures as an example...obviously this is not what I am really using. I don't know if this helps or not.
Off topic. I appreciate Prelude's posts. She is second to none with her knowledge and command of this and other languages. I was taken by surprise with her reply that's all. No hard feelings at all. Prelude used to be moree tolerant..but that was 2 1/2 years ago...time on this thread will wear you down.

What's the nature of this vector? Is it a vector of structs? And why does the data even get removed from the vector anyway, if it's just getting put right back in? If it's a vector of the structs, then .size() should give you the number of structs stored in the vector.

Shooting in the dark, perhaps the reason that putting the info back into the vector ends you up with garbage is because some of the data in the struct is dynamically allocated etc, and you haven't defined your own copy constructor? If in your destructor you delete some dynamic memory, then what ends up in the struct that you just pushed onto the vector will be a dangling pointer.

vector of the same struct. the data gets put into the vector by another application. I have a local structure that matches the structure in the vector in elements and size. I read what is in the vector and put it into my local structure. I then manipulate this data and write the new results back out to the vector. Does this make sense?

Quote:

---

For that I apolgize and will cease to post here in the future.

---

A quick, clean hari kari, with no whimpering. Much respect.

thanks 7stud you are most helpful! I decided to post more after reading MadCow's reply.

>>Does this make sense?
Now it does. Although I'm unclear on exactly how "another application" feeds data into the vector, I'll assume it's not relevant to the problem. On the other hand, why can't you just directly modify the elements in the vector? Seems like a waste to copy them out and then copy them back in. And have you considered my suggestion for why you might be getting garbage values yet?

I think I can simplify the problem. When I copy the data from a vector into a local structure, the data looks great in the local variables that are contained in the structure. The problem is this. In the same file in another procedure I am trying to use this local structure and copy the data. When I do this the data is all garbage (int's are equal to the max negative value ot an int type, etc, etc). I'm losing the data because it is local to the other procedure where I declared it. How can I fix this?

Hmmm, Im not a great programmer at all. But I think you tring to take data from a Vector, Modify the data. Then copy the data back to the vector? Maybe the values are garbage cause when you modified it, you curropted the data. The only way I can see it containing garbage is if you modified it the wrong way, you using uninitialized variables to modify the data, You are not accessing the real data cause you using pointer stuff or array stuff that is at the wrong location. Those are my thoughts on the matter. Not sure how to help with the code. I suck at programming lol. Hope you solve your problem. Im unsure how helpful everyone can be without seeing the real code though.

Is this code any close to what you were tring to do?

Code:

---

#include <iostream>
using namespace std;
struct names_a {
        names_a();
static int number_of_names;
char name[10];
};
int names_a::number_of_names=0;
names_a::names_a(){
        number_of_names++;
}
struct names_b {
names_b();
static int number_of_names;
char name[10];
};
int names_b::number_of_names=0;
names_b::names_b(){
        number_of_names++;
}

int main(){
names_a Kim;
names_b Modify_Kim;
for(int i=0;i<10;i++){
Kim.name[i]=NULL;
}
Kim.name[0]='K';
Kim.name[1]='i';
Kim.name[2]='m';
for(int i=0;i<10;i++){
Modify_Kim.name[i]=NULL;
}
for(int i=0;i<10 && Kim.name[i]!= NULL ;i++){
Modify_Kim.name[i]=Kim.name[i];
}
Modify_Kim.name[0]='H';
for(int i=0;i<10;i++){
Kim.name[i]=Modify_Kim.name[i];
}
for(int i=0;i<10 && Kim.name[i]!=NULL ;i++){
cout<<Kim.name[i];
}
cout<<endl;
cout<<Kim.number_of_names;
system("PAUSE");
return 0;
}

---

no this is not whta's happening at all. The data looks good when I copy it from the vector into the structure. I'll try to post code later. thanks!

First and foremost, using two structures with identical members sounds suspicious because I get the impression you're trying to do something like this when you say you're copying from one to the other:

Code:

---

struct names_a a;
struct names_b b;

fill_a(&a);
b = a; // Big no-no

---

Two instances of two structures are never compatible, even if they appear to be declared the same way. That's my first question about your playing with two structure types for the same data.

As I understand it, this is your problem: You have a vector of name_a objects that are already filled with valid data. You want to take each of these objects and copy the data into a name_b object presumably because you have a function that only works with the name_b type. Then you want to copy the modified data back into the original vector of name_a objects.

If that's a correct assessment of your issue, you have no choice but to copy data manually for a conversion:

Code:

---

name_a makea(name_b& b)
{
  name_a ret;

  ret.number_of_names = b.number_of_names;
  strcpy(ret.name, b.name);

  return ret;
}

name_b makeb(name_a& a)
{
  name_b ret;

  ret.number_of_names = a.number_of_names;
  strcpy(ret.name, a.name);

  return ret;
}

...

for (int i = 0; i < vsize; i++) {
  name_a a = makea(modify_data(makeb(v[i])));
  v[i] = a;
}

---

thanks Prelude! I already fixed the problem.

for the record, isn't prelude a guy?

I just went by the picture Prelude has under the profile. I could be mistaken and if so, I do apologize to Prelude. No offense intended.

>>for the record, isn't prelude a guy?
No, but you're not the first person to ever think so ;)

@JerryKelleyJr: Out of curiosity, what was the problem?

hunter...The problem was me. I did not state the problem clearly...this is due to my lack of experience. I sat down and gave what I was really trying to accomplish more thought. The solution was to copy one buffer to another using memcpy. See my next post on "memcpy use?" Off Topic, I didn't think Prelude was a guy...afterall there are a lot of masculine looking women who are very attractive...not that I'm saying Prelude's appearance is masculine.