Is it in the standard that one cannot declare a member of a struct that
uses a non-default constructor? Here is my simplified code; the Matrix
class was taken from the FAQ, and works well otherwise (error checking
was removed for simplicity).
#include <iostream>
#include <vector>
const int NUM_SEASONS = 4;
const int NUM_HALF_HOURS = 48;
//////////////////////////////////////// Matrix class taken from FAQ:
class Matrix
{
public:
Matrix(unsigned rows, unsigned cols);
~Matrix();
Matrix(const Matrix& m);
Matrix& operator=(const Matrix& m);
private:
unsigned rows_, cols_;
double* data_;
};
inline Matrix::Matrix( unsigned rows, unsigned cols)
: rows_(rows)
, cols_(cols)
{
data_ = new double[rows * cols];
}
inline Matrix::~Matrix ()
{
delete[] data_;
}
inline Matrix::Matrix( const Matrix& m) { }
inline Matrix& Matrix::operato r=(const Matrix& m) { return *this; }
//////////////////////////////////////// End of Matrix class from FAQ
struct Rcvr_values
{
Matrix signal(NUM_SEAS ONS, NUM_HALF_HOURS) ; // error is this line
};
struct Rcvr
{
std::vector<Rcv r_values> values;
};
int main()
{
Rcvr a;
return 0;
}
Using VC++ 7.1, I get the following compiler error:
test.cpp(37) : error C2061: syntax error : identifier 'NUM_SEASONS'
However, if I change the constructor of Matrix to:
inline Matrix::Matrix( unsigned rows = NUM_SEASONS,
unsigned cols = NUM_HALF_HOURS)
and I change Rcvr_values to:
struct Rcvr_values
{
Matrix signal;
};
then I get no compiler error.
--
Marcus Kwok 3 4178
Marcus Kwok wrote: Is it in the standard that one cannot declare a member of a struct that uses a non-default constructor?
No, but you are doing in the wrong way. struct Rcvr_values { Matrix signal(NUM_SEAS ONS, NUM_HALF_HOURS) ; // error is this line };
I think you know the answer really
struct Rcvr_values
{
Rcvr_values() : signal(NUM_SEAS ONS, NUM_HALF_HOURS) {}
Matrix signal;
};
john
Marcus Kwok wrote: Is it in the standard that one cannot declare a member of a struct that uses a non-default constructor? ... struct Rcvr_values { Matrix signal(NUM_SEAS ONS, NUM_HALF_HOURS) ; // error is this line }; ...
You can't "use" constructors (i.e. specify initializers) in the actual
declaration of the data member. The above syntax simply doesn't make any sense
in C++.
If you want to perform custom initialization of data member, you have to do it
in the initializer list of the enclosing struct's constructor:
struct Rcvr_values
{
Matrix signal;
Rcvr_values() : signal(NUM_SEAS ONS, NUM_HALF_HOURS)
{}
};
--
Best regards,
Andrey Tarasevich
Andrey Tarasevich <an************ **@hotmail.com> wrote: Marcus Kwok wrote: Is it in the standard that one cannot declare a member of a struct that uses a non-default constructor? ... struct Rcvr_values { Matrix signal(NUM_SEAS ONS, NUM_HALF_HOURS) ; // error is this line }; ...
You can't "use" constructors (i.e. specify initializers) in the actual declaration of the data member. The above syntax simply doesn't make any sense in C++.
If you want to perform custom initialization of data member, you have to do it in the initializer list of the enclosing struct's constructor:
struct Rcvr_values { Matrix signal;
Rcvr_values() : signal(NUM_SEAS ONS, NUM_HALF_HOURS) {} };
Thank you John and Andrey. What I believe is happening is that the line:
Matrix signal(...);
is interpreted by the compiler as a function declaration for a function
named "signal" that returns a Matrix, so it expected a typename
immediately after the open parenthesis.
--
Marcus Kwok This thread has been closed and replies have been disabled. Please start a new discussion. Similar topics |
by: lothar |
last post by:
re:
4.2.1 Regular Expression Syntax
http://docs.python.org/lib/re-syntax.html
*?, +?, ??
Adding "?" after the qualifier makes it perform the match in non-greedy or
minimal fashion; as few characters as possible will be matched.
the regular expression module fails to perform non-greedy matches as
described in the documentation: more than "as few characters as possible"
|
by: klaus triendl |
last post by:
hi,
recently i discovered a memory leak in our code; after some investigation i
could reduce it to the following problem:
return objects of functions are handled as temporary objects, hence their
dtor is called immediately and not at the end of the function. to be able to
use return objects (to avoid copying) i often assign them to a const
reference.
now, casting a const return object from a function to a non-const reference
to this...
|
by: Mario |
last post by:
Hello,
I couldn't find a solution to the following problem (tried
google and dejanews), maybe I'm using the wrong keywords?
Is there a way to open a file (a linux fifo pipe actually) in
nonblocking mode in c++? I did something ugly like
--- c/c++ mixture ---
mkfifo( "testpipe", 777);
|
by: Yves Glodt |
last post by:
Hello,
if I do this:
for row in sqlsth:
________pkcolumns.append(row.strip())
________etc
without a prior:
|
by: Adrian Herscu |
last post by:
Hi all,
In which circumstances it is appropriate to declare methods as non-virtual?
Thanx,
Adrian.
| |
by: Steve - DND |
last post by:
We're currently doing some tests to determine the performance of static vs
non-static functions, and we're coming up with some odd(in our opinion)
results. We used a very simple setup. One class had a static function, and
the one class had a non-static function. Both of these functions did the
exact same thing.
The test function:
public void Test(){
decimal y = 2;
decimal x = 3;
|
by: Ian825 |
last post by:
I need help writing a function for a program that is based upon the various operations of a matrix and I keep getting a "non-aggregate type" error. My guess is that I need to dereference my pointers, but I'm not sure. Please help.
The code:
void equate(matrix *A, matrix *B)
{
int i, j;
assert(A.row_dim == B.col_dim && A.col_dim == B.col_dim);
for(i=0; i < A.row_dim; i++)
for(j=0; j < A.col_dim; j++)
|
by: amitvps |
last post by:
Secure Socket Layer is very important and useful for any web application but it brings some problems too with itself. Handling navigation between secure and non-secure pages is one of the cumbersome jobs.
When a non-secure page references a secure page with relative URL, the web server generates error until absolute URL with https prefix is used. On the other hand when a secure page references a non-secure page, the non-secure page will be...
|
by: =?UTF-8?B?Ik1hcnRpbiB2LiBMw7Z3aXMi?= |
last post by:
PEP 1 specifies that PEP authors need to collect feedback from the
community. As the author of PEP 3131, I'd like to encourage comments
to the PEP included below, either here (comp.lang.python), or to
python-3000@python.org
In summary, this PEP proposes to allow non-ASCII letters as
identifiers in Python. If the PEP is accepted, the following
identifiers would also become valid as class, function, or
variable names: Löffelstiel,...
|
by: puzzlecracker |
last post by:
is it even possible or/and there is a better alternative to accept
input in a nonblocking manner?
|
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: tracyyun |
last post by:
Dear forum friends,
With the development of smart home technology, a variety of wireless communication protocols have appeared on the market, such as Zigbee, Z-Wave, Wi-Fi, Bluetooth, etc. Each protocol has its own unique characteristics and advantages, but as a user who is planning to build a smart home system, I am a bit confused by the choice of these technologies. I'm particularly interested in Zigbee because I've heard it does some...
|
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: 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: adsilva |
last post by:
A Windows Forms form does not have the event Unload, like VB6. What one acts like?
| |
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...
| |