473,327 Members | 1,997 Online
Bytes | Software Development & Data Engineering Community
Post Job

Home Posts Topics Members FAQ

Join Bytes to post your question to a community of 473,327 software developers and data experts.

Static members

I want to declare a std::map as an static member of a class, so I wrote
this code:

#include <map>
#include <string>

using namespace std;

namespace msu
{
class Test
{
public:
static map<string, intmt;
};
}

int main()
{
map<string, intmsu::Test::mt["Jan"] = 1;

return 0;
}

I've done several searches in google and all the pages show code like
the one above to declare, define and initialize static data members.
Wll, that doesn' work and I don't kno why.
When I compiled it with g++ I get this error message:

test.cpp: In function `int main()':
test.cpp:17: error: size of array `mt' has non-integral type `const
char[4]'
test.cpp:17: error: conflicting declaration 'std::map<std::string, int,
std::less<std::string>, std::allocator<std::pair<const std::string,
int msu::Test::mt[1]'
test.cpp:11: error: 'msu::Test::mt' has a previous declaration as
`std::map<std::string, int, std::less<std::string>,
std::allocator<std::pair<const std::string, int msu::Test::mt'
test.cpp:17: error: conversion from `int' to non-scalar type
`std::map<std::string, int, std::less<std::string>,
std::allocator<std::pair<const std::string, int >' requested

I appreciate your help.

Oct 27 '06 #1
2 2583

<ga******@gmail.comwrote in message
news:11*********************@k70g2000cwa.googlegro ups.com...
>I want to declare a std::map as an static member of a class, so I wrote
this code:

#include <map>
#include <string>

using namespace std;

namespace msu
{
class Test
{
public:
static map<string, intmt;
Ok, this declares the map. Now you need to define it, outside the class.
};
}
Define it here:

map<string,intmsu::Test::mt;

(I think that's right. Does it need to be initialized smoehow? Anyone
know?)
int main()
{
map<string, intmsu::Test::mt["Jan"] = 1;
This attempts to both define the map and set one member of it. But the
compiler sees it as re-declaring mt as an array of maps with a size given by
"Jan", which isn't a valid integral constant.

Define the map separately (as shown above), and then just use it in main().
>
return 0;
}

I've done several searches in google and all the pages show code like
the one above to declare, define and initialize static data members.
I don't see an example like that. (I haven't looked very long, though.)
Look again, for "static member map".
Wll, that doesn' work and I don't kno why.
When I compiled it with g++ I get this error message:

test.cpp: In function `int main()':
test.cpp:17: error: size of array `mt' has non-integral type `const
char[4]'
That's because you're declaring an array, trying to pass "Jan" as the size.
test.cpp:17: error: conflicting declaration 'std::map<std::string, int,
std::less<std::string>, std::allocator<std::pair<const std::string,
int msu::Test::mt[1]'
test.cpp:11: error: 'msu::Test::mt' has a previous declaration as
`std::map<std::string, int, std::less<std::string>,
std::allocator<std::pair<const std::string, int msu::Test::mt'
Those are because the new declaration doesn't match the original.
test.cpp:17: error: conversion from `int' to non-scalar type
`std::map<std::string, int, std::less<std::string>,
std::allocator<std::pair<const std::string, int >' requested

I appreciate your help.
-Howard
Oct 27 '06 #2
Howard wrote:
<ga******@gmail.comwrote:
I want to declare a std::map as an static member of a class, so I wrote
this code:

#include <map>
#include <string>

using namespace std;

namespace msu
{
class Test
{
public:
static map<string, intmt;

Ok, this declares the map. Now you need to define it, outside the class.
Right. See the FAQ:
http://www.parashift.com/c++-faq-lit...html#faq-10.11
};
}

Define it here:

map<string,intmsu::Test::mt;

(I think that's right. Does it need to be initialized smoehow? Anyone
know?)
It will be default initialized to be empty, but one could use a helper
class to initialize it here:

template<class K, class V>
class MapInitializer
{
typedef std::map<K,VMap;
Map m_;
public:
operator Map() const { return m_; }

MapInitializer& Add( const K& k, const V& v )
{
m_[k] = v;
return *this;
}
};

map<string,intmsu::Test::mt
= MapInitializer<string, int>()
.Add( "Str 1", 9 )
.Add( "Str 2", 42 )
.Add( "Str 3", 314 );

This is particularly useful if that map should be a *const* static
member.

Cheers! --M

Oct 27 '06 #3

This thread has been closed and replies have been disabled. Please start a new discussion.

Similar topics

3
by: DanielBradley | last post by:
Hello all, I have recently been porting code from Linux to cygwin and came across a problem with static const class members (discussed below). I am seeking to determine whether I am programming...
8
by: Scott J. McCaughrin | last post by:
The following program compiles fine but elicits this message from the linker: "undefined reference to VarArray::funct" and thus fails. It seems to behave as if the static data-member:...
15
by: Samee Zahur | last post by:
Question: How do friend functions and static member functions differ in terms of functionality? I mean, neither necessarily needs an object of the class to be created before they are called and...
6
by: lovecreatesbeauty | last post by:
Hello Experts, Why static data members can be declared as the type of class which it belongs to? Inside a class, non-static data members such as pointers and references can be declared as...
13
by: Adam H. Peterson | last post by:
I just made an observation and I wondered if it's generally known (or if I'm missing something). My observation is that static protected members are essentially useless, only a hint to the user. ...
3
by: Mauzi | last post by:
hi, this may sound odd and noob like, but what is the 'big' difference between static and non-static funcitons ? is there any performace differnce? what is the best way to use them ? thnx ...
6
by: Matt | last post by:
All of a sudden all my C# apps require the keyword static on all global fields and methods that I create. Even in the simplest of console apps. Can someone tell me what I have inadvertenly set in...
11
by: dee | last post by:
OleDbCommand class like many .NET classes has the following description in its help file: "Thread Safety Any public static (Shared in Visual Basic) members of this type are safe for...
11
by: Kevin Prichard | last post by:
Hi all, I've recently been following the object-oriented techiques discussed here and have been testing them for use in a web application. There is problem that I'd like to discuss with you...
8
by: crjjrc | last post by:
Hi, I've got a base class and some derived classes that look something like this: class Base { public: int getType() { return type; } private: static const int type = 0; };
0
by: DolphinDB | last post by:
Tired of spending countless mintues downsampling your data? Look no further! In this article, you’ll learn how to efficiently downsample 6.48 billion high-frequency records to 61 million...
0
by: Vimpel783 | last post by:
Hello! Guys, I found this code on the Internet, but I need to modify it a little. It works well, the problem is this: Data is sent from only one cell, in this case B5, but it is necessary that data...
0
by: jfyes | last post by:
As a hardware engineer, after seeing that CEIWEI recently released a new tool for Modbus RTU Over TCP/UDP filtering and monitoring, I actively went to its official website to take a look. It turned...
0
by: ArrayDB | last post by:
The error message I've encountered is; ERROR:root:Error generating model response: exception: access violation writing 0x0000000000005140, which seems to be indicative of an access violation...
1
by: CloudSolutions | last post by:
Introduction: For many beginners and individual users, requiring a credit card and email registration may pose a barrier when starting to use cloud servers. However, some cloud server providers now...
1
by: Defcon1945 | last post by:
I'm trying to learn Python using Pycharm but import shutil doesn't work
1
by: Shællîpôpï 09 | last post by:
If u are using a keypad phone, how do u turn on JavaScript, to access features like WhatsApp, Facebook, Instagram....
0
by: Faith0G | last post by:
I am starting a new it consulting business and it's been a while since I setup a new website. Is wordpress still the best web based software for hosting a 5 page website? The webpages will be...
0
isladogs
by: isladogs | last post by:
The next Access Europe User Group meeting will be on Wednesday 3 Apr 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 former...

By using Bytes.com and it's services, you agree to our Privacy Policy and Terms of Use.

To disable or enable advertisements and analytics tracking please visit the manage ads & tracking page.