C / C++ / MFC

31-May-07 13:02

Hi all:

Below is my problem:

I declared a class called "WordTable" in a .h file.:

<code>class WordTable
{
public:
typedef vector<streampos> OccurrenceList;

private:
......

public:
OccurrenceList& getOccurrences(string word);
};</code>

later in a .cpp file.

I defined the function "getOccurrences()" as following:

<code>OccurrenceList& WordTable::getOccurrences(string word)
{
OccurrenceList list;
return list;
}</code>

But it seems that the complier does not recognize "OccurrenceList" at all. I am sure that I have included the proper header file.
I tried to fix the errors by explicitly declare "typedef vector<streampos> OccurrenceList;" at the top of the .cpp file, it worked.

Can anyone help?
Thank you

Christian Graus31-May-07 13:29

Christian Graus

31-May-07 13:29

I believe that you need to do the typedef outside the class. Better yet, don't do it, those things are nasty, they just make your code unreadable.

Christian Graus - Microsoft MVP - C++
Metal Musings - Rex and my new metal blog
"I am working on a project that will convert a FORTRAN code to corresponding C++ code.I am not aware of FORTRAN syntax" ( spotted in the C++/CLI forum )

Stephen Hewitt31-May-07 14:26

Stephen Hewitt

31-May-07 14:26

Christian Graus wrote:
I believe that you need to do the typedef outside the class. Better yet, don't do it, those things are nasty, they just make your code unreadable.

Nothing's wrong with typedefs; they make code more readable not less so. Nothing's wrong with typedefs inside class definitions either: in fact in some cases it's just good encapsulations and is exactly where they should go. The OP’s problem was simply that the use of a member typedef needs to be qualified with the containing class name if used outside the containing class, just like for any other member.

Steve

Christian Graus31-May-07 18:28

Christian Graus

31-May-07 18:28

Stephen Hewitt wrote:
they make code more readable not less so.

That's a matter of opinion. I've worked on code that contained a ton of STL containers, all typedefed, and it was plain illegible.

Stephen Hewitt wrote:
The OP’s problem was simply that the use of a member typedef needs to be qualified with the containing class name if used outside the containing class, just like for any other member.

Yes, I realised that, but pulling it out seemed the simplest solution.

Stephen Hewitt31-May-07 18:57

Stephen Hewitt

31-May-07 18:57

Christian Graus wrote:
That's a matter of opinion. I've worked on code that contained a ton of STL containers, all typedefed, and it was plain illegible.

In the end almost anything can be considered a matter of opinion, but I’ll explain some instances in which typedefs can be useful. A STL std::set looks something like this:

template <class _K, class _Pr = less<_K>, class _A = allocator<_K> >
class set;

If we have one of these beasts where we’ve made explicit use of all three template arguments we’d have to specify the whole long type in every use. A simple typedef with a descriptive name eliminates all this. Surely this is a simplification, especially since some of the arguments are implementation details. Say, at a later stage, we make a design decision to change the allocator used: we would have to go through the code and change all uses of the type. If a typedef is used we can make the change in one place. This is an example of the general design principle that, if possible, a single design decision should be expressed in a single place (or as few places as possible). Another example is generic programming; STL containers use typedefs with standard names to expose implementation dependent types in a standard manner which enables uniform usage despite the differences.

Steve

Mark Salsbery31-May-07 14:08

Mark Salsbery

31-May-07 14:08

If you must (against Christian's advice) nest the typedef you need to use a scope resolution
operator to reference the nested class/type from outside the class:

WordTable::OccurrenceList& WordTable::getOccurrences(string word)
{
    WordTable::OccurrenceList list; // Note the "WordTable::" is optional here
                                    //   since you're already in the WordTable class scope
 
    return list; //<code><--- Bug - returning a reference to a temporary variable!</code>
}

A template defines a class. If you nest the class in another class then you need to resolve the
scope anywhere outside of the class, as shown above.

Plus there's a bug, noted above Smile | :)

Mark

"Posting a VB.NET question in the C++ forum will end in tears." Chris Maunder

C_Zealot31-May-07 14:29

31-May-07 14:29

Hi Mark:

Thank you for your solution. This is EXACTLY what my problem was!!!!
So happy to get it solved.

Thank you again.

CTreeCtrl - GetSelectedItem [modified]

Jeffrey Walton31-May-07 20:39

Jeffrey Walton

31-May-07 20:39

Hi C_Zealot,

Try a forward declaration (in the h file, or the cpp file):

class OccurrenceList;

Jeff

Vaclav_31-May-07 12:26

Vaclav_

31-May-07 12:26

Please help me find a simple example of CTreeCtrl (view not dialog) actually using TVN_SELCHANGED message and GetSelectedItem function. My code always returns first item in the tree and the MS CmnCtrl1 sample code refuses to give me the whole text of the selected item. I get only first character. It should return CString.

Thanks for reading
Vaclav

I got it!
I have neglected to bypass first TVN_SELCHANGED message which gets posted on initial drawing of first node of the tree! Hence I always see first node "selected".

-- modified at 21:57 Thursday 31st May, 2007

Naveen31-May-07 15:24

Naveen

31-May-07 15:24

Vaclav_Sal wrote:
refuses to give me the whole text of the selected item

How did you verify that? Through debugging? Try putting a message box. If _UNICODE is define in your project, you must set some settings of MSDEV.

tools->options->Debug-> Now tick the "Display UNICODE string check box".

nave

OpenedFileFinder

Vaclav_31-May-07 15:55

Vaclav_

31-May-07 15:55

Nave,
I changed to display UNICODE and it works now. However I am using MS sample code and did not find UNICODE defined!
Thanks for your help

Naveen31-May-07 16:01

Naveen

31-May-07 16:01

Vaclav_Sal wrote:
and did not find UNICODE defined!

Check the following location.

project settings->C++->And in the Preprocess definitions edit box check _UNICODE is defined.

nave

[OpenedFileFinder]

Errors? C++, play with reference

Vaclav_31-May-07 16:28

Vaclav_

31-May-07 16:28

You are absolutely correct!
Thanks

C_Zealot31-May-07 11:55

Re: Errors? C++, play with reference

31-May-07 11:55

Hi all:

When I am trying to write the function definition for:
OccurrenceList& getOccurrences(string word);

I wrote:
<code>......
typedef vector<streampos> OccurrenceList;
......
78: OccurrenceList& WordTable::getOccurrences(string word) {
79: OccurrenceList list;
80: return list; //Return nothing to simplify the function for debugging.
81: }</code>

But I have 5 (!!) errors, they are:
78: error C2143: syntax error : missing ';' before '&';
78: error C4430: missing type specifier - int assumed. Note: C++ does not support default-int;
79: error C4430: missing type specifier - int assumed. Note: C++ does not support default-int;
79: 'int &WordTable::getOccurrences(std::string)' : overloaded function differs only by return type from 'WordTable::OccurrenceList &WordTable::getOccurrences(std::string)';
79: 'WordTable::getOccurrences' : redefinition; different basic types;

When I commented out this function, the rest of my program ran sweet. I really do not know what caused those problems.

Thank you

Mark Salsbery31-May-07 12:13

Mark Salsbery

31-May-07 12:13

It looks like the compiler doesn't know what a "OccurrenceList" type is at that point.

Are you missing a header file containing the declaration of the class?

Mark

"Posting a VB.NET question in the C++ forum will end in tears." Chris Maunder

Re: Errors? C++, play with reference

C_Zealot31-May-07 12:16