I've been having some problems with pointers and such.This is homework,
so I don't want people writing codeand telling me to use it. I just
want some direction on what isn't working.
here is the structure prototype:
struct Books
{
string ISBN;
string title;
string author;
string publisher;
float price;
int onHand;
};
here is the call:
swapElems(book, startscan, minIndex);
book is the struct, startscan is an int for the subscript, and so is
minIndex
here is the func with lines in question:
swapElems(Books *x, int startscan, int minIndex)
{
Books temp = { "", "", "", "", 0.0f, 0 };
temp = *x[startscan];
*x[startscan] = *x[minIndex];
*x[minIndex] = temp;
}
I get the four errors that say illegal indirection and the compiler is
MS visual studio 2003, not that it even matters. I need to do this, but
more importantly, I need to learn it TOO. 4 1368
* pc****@gmail.co m: I've been having some problems with pointers and such.This is homework, so I don't want people writing codeand telling me to use it. I just want some direction on what isn't working.
here is the structure prototype: struct Books { string ISBN; string title; string author; string publisher; float price; int onHand; };
Are you sure this is a prototype of a collection of Books, and not a
single Book?
It looks like a single Book to me.
here is the call: swapElems(book, startscan, minIndex);
If you defined 'book' etc. then perhaps it could tell others something.
book is the struct, startscan is an int for the subscript, and so is minIndex
here is the func with lines in question: swapElems(Books *x, int startscan, int minIndex) { Books temp = { "", "", "", "", 0.0f, 0 };
temp = *x[startscan]; *x[startscan] = *x[minIndex]; *x[minIndex] = temp; }
The best advice is to NOT USE RAW POINTERS or raw arrays until you gain
much more experience.
To represent a collection of books, do something like
std::vector<Boo k> books;
or
std::vector<Boo k> books(500);
To swap e.g. the books at indices 5 and 13, do
std::swap( books.at(5), books.at(13) );
I get the four errors that say illegal indirection and the compiler is MS visual studio 2003, not that it even matters. I need to do this, but more importantly, I need to learn it TOO.
Use the standard library, as explained above.
Keep away from pointers and raw arrays.
--
A: Because it messes up the order in which people normally read text.
Q: Why is it such a bad thing?
A: Top-posting.
Q: What is the most annoying thing on usenet and in e-mail?
Here is my object instance declaration
Books book[100];
I know I don't want to use vectors right now, I just need to learn how
to point to this in a way to change my values
* pc****@gmail.co m: Here is my object instance declaration
Books book[100];
I know I don't want to use vectors right now, I just need to learn how to point to this in a way to change my values
Well, if you don't want the easy, professional way, but rather the
difficult, unprofessional way, i.e. as many hurdles and problems and
bugs as possible, there's not much advice to give except delve into it
and try the most difficult and hard to grok you can think of first: that
should presumably give you enough problems.
Otherwise, replace that declaration with
std::vector<Boo k> books( 100 );
Note the placement of the "s": the type Book describes a single book
(not plural), wheras the variable is a collection of book (plural).
Now you can write e.g.
std::cout << books.at(3).tit le << std::endl;
And you'll discover that that magic number 100 is completely
meaningless, because the vector, as opposed to the raw array, can be
very easily resized to accomodate any number of books.
--
A: Because it messes up the order in which people normally read text.
Q: Why is it such a bad thing?
A: Top-posting.
Q: What is the most annoying thing on usenet and in e-mail?
> here is the func with lines in question: swapElems(Books *x, int startscan, int minIndex) { Books temp = { "", "", "", "", 0.0f, 0 };
temp = *x[startscan]; *x[startscan] = *x[minIndex]; *x[minIndex] = temp; }
x[n] actually is a Book not a pointer, so you don't need to dereference
it. That is, instead of writing
temp = *x[startscan];
you should have written:
temp = x[startscan];
The rationale is x[n] is always interpreted as *(x+n), which is in
itself a dereferencing operation.
Regards,
Ben This thread has been closed and replies have been disabled. Please start a new discussion. Similar topics |
by: Christian F |
last post by:
Hi, I'm a C-newbie and I would like to know if I am doing something
wrong in the code below. It is working, but I'm afraid it might not be
correct because I don't really understand everything of it. There are
lots of pointers and pointers to pointers which makes me confused.
First my typedef:
typedef struct
{
double re;
|
by: John Hanley |
last post by:
I working in C. I haven't paid much attention to void pointers in the past,
but I am wondering if I can use them for my various linked lists to save
work.
I have two different linked lists that each use nodes of different structs.
However the principle of my adding to the linked lists and removing them is
the same. So will it work to have these functions accept a void pointer as
an argument for the list and a void pointer as an...
|
by: x-pander |
last post by:
Is is guaranteed, that a pointer to any object in C points exactly at the
lowest addressed byte of this object?
Specifcally is it possible for any platform/os/compiler combination that:
(char *)v != (void *)v
where v is an int variable for example.
If so, any real-life examples?
|
by: sunglo |
last post by:
Some time a go, in a discussion here in comp.lang.c, I learnt that it's
better not to use a (sometype **) where a (void **) is expected (using
a cast). Part of the discussion boiled down to the rule: if I cast a
(sometype **) to a (void **) I am making a number of assumptions about
the implementation's (void **) representation and length. Specifically,
if I do the above cast I'm assuming that a (sometype **) and a (void
**) have the same...
|
by: Paminu |
last post by:
Why make an array of pointers to structs, when it is possible to just make
an array of structs?
I have this struct:
struct test {
int a;
int b;
| |
by: Johan Tibell |
last post by:
Could someone outline the pros and cons of typedefing pointers to
structs like this?
typedef struct exp_ {
int val;
struct exp_ *child;
} *exp;
(This is straight from memory so it might not even compile.)
|
by: Zytan |
last post by:
I know there are no pointers in C#, but if you do:
a = b;
and a and b are both arrays, they now both point to the same memory
(changing one changes the other). So, it makes them seem like
pointers.
Can someone please explain why? thanks.
Zytan
|
by: dev_15 |
last post by:
Hi, I'm going through some code and thought that this allocates an
array of structs but its supposed according to comments to allocate an
array of pointer to structs. What does it actually do
ptrLogArray = new structDisplayLogData *;
// iCount = 50 structDisplayLogData is a strcuture of data
Thanks
|
by: hal |
last post by:
Hi,
I'm trying to make an array of pointers to 'TwoCounts' structs, where
the size of the array is arraySize. Right now I'm just mallocing
enough space for all the pointers to the structs, and mallocing space
for the pointer 'countPtr' in each struct, but do I need to do
anything else? Thanks.
typedef struct TwoCounts {
int *countPtr;
|
by: marktang |
last post by:
ONU (Optical Network Unit) is one of the key components for providing high-speed Internet services. Its primary function is to act as an endpoint device located at the user's premises. However, people are often confused as to whether an ONU can Work As a Router. In this blog post, we’ll explore What is ONU, What Is Router, ONU & Router’s main usage, and What is the difference between ONU and Router. Let’s take a closer look !
Part I. Meaning of...
|
by: Oralloy |
last post by:
Hello folks,
I am unable to find appropriate documentation on the type promotion of bit-fields when using the generalised comparison operator "<=>".
The problem is that using the GNU compilers, it seems that the internal comparison operator "<=>" tries to promote arguments from unsigned to signed.
This is as boiled down as I can make it.
Here is my compilation command:
g++-12 -std=c++20 -Wnarrowing bit_field.cpp
Here is the code in...
| |
by: jinu1996 |
last post by:
In today's digital age, having a compelling online presence is paramount for businesses aiming to thrive in a competitive landscape. At the heart of this digital strategy lies an intricately woven tapestry of website design and digital marketing. It's not merely about having a website; it's about crafting an immersive digital experience that captivates audiences and drives business growth.
The Art of Business Website Design
Your website is...
|
by: Hystou |
last post by:
Overview:
Windows 11 and 10 have less user interface control over operating system update behaviour than previous versions of Windows. In Windows 11 and 10, there is no way to turn off the Windows Update option using the Control Panel or Settings app; it automatically checks for updates and installs any it finds, whether you like it or not. For most users, this new feature is actually very convenient. If you want to control the update process,...
|
by: agi2029 |
last post by:
Let's talk about the concept of autonomous AI software engineers and no-code agents. These AIs are designed to manage the entire lifecycle of a software development project—planning, coding, testing, and deployment—without human intervention. Imagine an AI that can take a project description, break it down, write the code, debug it, and then launch it, all on its own....
Now, this would greatly impact the work of software developers. The idea...
|
by: isladogs |
last post by:
The next Access Europe User Group meeting will be on Wednesday 1 May 2024 starting at 18:00 UK time (6PM UTC+1) and finishing by 19:30 (7.30PM).
In this session, we are pleased to welcome a new presenter, Adolph Dupré who will be discussing some powerful techniques for using class modules.
He will explain when you may want to use classes instead of User Defined Types (UDT). For example, to manage the data in unbound forms.
Adolph will...
|
by: TSSRALBI |
last post by:
Hello
I'm a network technician in training and I need your help.
I am currently learning how to create and manage the different types of VPNs and I have a question about LAN-to-LAN VPNs.
The last exercise I practiced was to create a LAN-to-LAN VPN between two Pfsense firewalls, by using IPSEC protocols.
I succeeded, with both firewalls in the same network. But I'm wondering if it's possible to do the same thing, with 2 Pfsense firewalls...
|
by: 6302768590 |
last post by:
Hai team
i want code for transfer the data from one system to another through IP address by using C# our system has to for every 5mins then we have to update the data what the data is updated we have to send another system
| |
by: bsmnconsultancy |
last post by:
In today's digital era, a well-designed website is crucial for businesses looking to succeed. Whether you're a small business owner or a large corporation in Toronto, having a strong online presence can significantly impact your brand's success. BSMN Consultancy, a leader in Website Development in Toronto offers valuable insights into creating effective websites that not only look great but also perform exceptionally well. In this comprehensive...
| |