std::map, fundamental get started problem RESOLVED - ATL / WTL / STL Discussion Boards

bkelly139-Jun-13 10:42

9-Jun-13 10:42

Windows 7, Visual Studio 2008, MFC, C++, Dialog

My application makes use of an std::map, inserting records with the following:

m_tmats_definition_map[ the_key ] =  m_one_definition_record;

the_key is a CString and m_one_definition_record is a structure of several CStrings and a few various fields such as integers.

That seems to be working. Now in the event something does not work out right I want some error checking. I am not finding much of anything concerning run time checking on this insert operation. Probably not looking in the right places or using the right search phrase. Where can I look to find a good discussion on this topic?

Thanks for your time
If you work with telemetry, please check this bulletin board: http://www.bkelly.ws/irig_106/

Re: std::map and error checking

Garth J Lancaster9-Jun-13 13:18

Garth J Lancaster

9-Jun-13 13:18

ouch - hard question - I just had a look and its a right PITA - 'Dinkumware' and SGI used to have good manuals (and even finding what exceptions are thrown within is hard enough)

SGI's manual page for MAP is ... http://www.sgi.com/tech/stl/Map.html[^]

that may give you a start point - what sort of error's do you expect ? dont forget that map doesnt throw an error for a duplicate key value (the commonest issue I guess) - it simply replaces the existing value... for that reason, you should use find() first on the map to see if the value already exists

'g'

Re: std::map and error checking

bkelly139-Jun-13 14:16

bkelly13

9-Jun-13 14:16

I don't know what sort of errors to expect. Isn't that one of the joys of software? <grin>
Good link.
Good point with the Find(). I do want to know if there are duplicates and will incorporate that.

Thanks for your time
If you work with telemetry, please check this bulletin board: http://www.bkelly.ws/irig_106/

Re: std::map and error checking

Richard MacCutchan9-Jun-13 21:23

Richard MacCutchan

9-Jun-13 21:23

You need to check return values of function calls that provide information. See here[^] for the insert function.

Use the best guess

Re: std::map and error checking

MicroVirus11-Jun-13 12:07

MicroVirus

11-Jun-13 12:07

In this case, there's nothing you need to do. If something goes wrong, it'll throw a C++ exception. Most likely causes will be that a new element can't be constructed, or that there is insufficient memory.
But maybe this is not what you meant. You say you want error checking; why do you want error checking? What is that you want to accomplish? Perhaps the solution is different.

status display in a dialog

bkelly139-Jun-13 5:17

bkelly13

9-Jun-13 5:17

Windows 7, Visual Studio MFC, C++, dialog based project

A dialog is to have a status display area. The code will add lines of text. My preference is for each new line of text to be added to the bottom and have the display scroll up. The user will not be able to edit the text, but it would be nice to be able to capture it with ctl-c to paste somewhere else.

I tried an edit control but each update wipes out the previous text.
List box seems to be the simplest control, yet still has many user accessible features.

I would like to read your reccomendations.

Thanks for your time
If you work with telemetry, please check this bulletin board: http://www.bkelly.ws/irig_106/

Re: status display in a dialog

Garth J Lancaster9-Jun-13 14:53

Garth J Lancaster

9-Jun-13 14:53

have a look at this - its what I used for years when I did MFC

A Logging Listbox Control[^]

[edit] I can probably remember how to use it in a Dialog based app if you think you want to use it
Joseph's site is http://www.flounder.com/logctl.htm[^] [/edit]

'g'

std::map, fundamental get started problem RESOLVED

bkelly139-Jun-13 4:04

bkelly13

9-Jun-13 4:04

Windows 7, Visual Studio 2008, MFC, CPP, std::map
I am trying to get an std::map working. I have tried several permutations and patterned it after some tutorials found with a search. Still I am unable to get it right and to decipher the error message.
Please assist with this problem.
The setup

XML

typedef struct
{
   unsigned int   identifier_location;
   unsigned int   count_found;
   CString        key;
   CString        token[ MAX_TOKEN_COUNT ];
}     td_tmats_attributes_definitions;

td_tmats_attributes_definitions    m_one_definition_record;

std::map < CString, td_tmats_attributes_definitions > m_tmats_definition_map;
//          ^ the key    ^the data to store
// below is an alternate declaration.
std::map < string, td_tmats_attributes_definitions > m_tmats_definition_map_string;

And now the code

CString  the_key;
…
The code:
// The primary insertion code
 m_tmats_definition_map.insert( the_key, m_one_definition_record );
// the alternate
string str_key = the_key;
//            m_tmats_definition_map_string.insert( the_key, m_one_definition_record );

Neither of the two options will compile.

I was prepared to post the error message, but I have a strong suspicion that reader will know my error with little effort and the long text from VS output box will only clutter things up. Let me know if you want to see the error text.

Please tell me what I need to change.

Thanks for your time
If you work with telemetry, please check this bulletin board: http://www.bkelly.ws/irig_106/

modified 9-Jun-13 12:44pm.

Re: std::map, fundamental get started problem

pasztorpisti9-Jun-13 4:19

pasztorpisti

9-Jun-13 4:19

C++

m_tmats_definition_map.insert( std::make_pair(the_key, m_one_definition_record) );

C++

m_tmats_definition_map[the_key] = m_one_definition_record;

std::make_pair should be in the <utility> include.

Re: std::map, fundamental get started problem RESOLVED

bkelly139-Jun-13 4:46

bkelly13

9-Jun-13 4:46

As you already know, that compiles. I see the second option as being a bit more clear and used it.
Thank you for your time.

Thanks for your time
If you work with telemetry, please check this bulletin board: http://www.bkelly.ws/irig_106/

CFileException, discover reasons RESOLVED

bkelly138-Jun-13 10:05

bkelly13

8-Jun-13 10:05

Windows 7, 64 bit, Visual Studio 2008, MFC, C++

After a long series of searches looking for a nice method of reading from a text file into CString I arrived at the following:

<br />
CStdioFile definition_file;<br />
try<br />
      {<br />
         definition_file.Open( m_definition_file_name, CFile::modeRead );<br />
      }<br />
      catch( CFileException e )<br />
      {<br />
         e.m_cause;<br />
      }<br />

This is from the VS help utility:

<br />
catch( CFileException* e )<br />
{<br />
   if( e->m_cause == CFileException::fileNotFound )<br />
      printf( "ERROR: File not found\n")<br />
   e->Delete();<br />
}<br />

This leads to the concept

<br />
if( e->m_cause == CFileException::fileNotFound )<br />
      printf( "ERROR: File not found\n");<br />
elseif( e->m_cause == CFileException::generic )<br />
      printf( "ERROR: An unspecified error occurred.\n");<br />
elseif  etc etc<br />

Is there a better way of capturing the text of the error rather than an if/else/else/else sequence?
Note: I am open to any type of suggestion. The goal is to read a CSV text file and parse it into a std::map.

Thanks for your time
If you work with telemetry, please check this bulletin board: http://www.bkelly.ws/irig_106/

Re: CFileException, discover reasons

Richard MacCutchan8-Jun-13 21:40

Richard MacCutchan

8-Jun-13 21:40

Use the GetErrorMessage[^] member function.

Use the best guess

Re: CFileException, discover reasons RESOLVED

bkelly139-Jun-13 3:54

bkelly13

9-Jun-13 3:54

Cool.
Thank you.

Thanks for your time
If you work with telemetry, please check this bulletin board: http://www.bkelly.ws/irig_106/

Re: CFileException, discover reasons

bkelly139-Jun-13 6:11

bkelly13

9-Jun-13 6:11

Oops, I have a follow up on this.
Declarations:

CSS

CFileException     get_error_message;
 const unsigned int ERROR_MAX = 64;
 char  char_error_text[ ERROR_MAX ];
 LPTSTR ptr_error_text = &char_error_text[0];
 CString final_error_message = "";

Code:

m_definition_file_name += "x";
try
{
   m_definition_file.Open( m_definition_file_name, CFile::modeRead );
   get_error_message.GetErrorMessage( ptr_error_text, ERROR_MAX, NULL );
   final_error_message = char_error_text;
   error_number = GetLastError();

}
catch( CFileException e )
{ code }
catch( ... )
{ code }
{

The line m_definition_file_name += "x" forces the file name to be incorrect.

Char array char_error_text winds up with "No error occurred." while error_number gets 0 (zero)
When the line error_number = GetLastErrror is moved directly beneath the open command, it get the value 2 (two). But that consumes the last error and get_error_message does not get anything.
Nothing is thrown and neither catch is activated.

What do I need to change to use this CFileException?

Thanks for your time
If you work with telemetry, please check this bulletin board: http://www.bkelly.ws/irig_106/

Re: CFileException, discover reasons

Richard MacCutchan9-Jun-13 9:23

Richard MacCutchan

9-Jun-13 9:23

I don't understand what you are doing here; it should be:

C++

try
{
   // code to open the CFile
}
catch (CFileException ce)
{
    TCHAR message[132];
    if (ce.GetErrorMessage(message, 132, NULL)
    {
        // display the contents of the message buffer
    }
}

Use the best guess

Re: CFileException, discover reasons

bkelly139-Jun-13 9:43

bkelly13

9-Jun-13 9:43

Hello,
I don't see what you have different. Second, when the file does not exist, this Open method does not throw an exception, so none of the try/catch matters. I had a catch(...) at the bottom and it was not entered.

Thanks for your time
If you work with telemetry, please check this bulletin board: http://www.bkelly.ws/irig_106/

Re: CFileException, discover reasons

Richard MacCutchan9-Jun-13 20:41

Richard MacCutchan

9-Jun-13 20:41

If the open function does not throw an error then you need to check the return value and call GetLastError() to find out why, as described here[^]. Alternatively you can throw a new exception like:

C++

try
{
   if (!m_definition_file.Open(m_definition_file_name, CFile::modeRead))
   {
       DWORD error_number = GetLastError();
       throw new CFileException::OsErrorToException(error_number);
   }
}
catch( CFileException e )
{
    // handle the exception
}

Note that when calling GetLastError() you must call it immediately after the failing API function call, otherwise its return may not be valid.

Use the best guess

tried FormatMessage()

bkelly139-Jun-13 7:07

bkelly13

9-Jun-13 7:07

I have also tried this.
Declarations:

CSS

const unsigned int ERROR_MAX = 64;
char  char_error_text[ ERROR_MAX ];
LPTSTR ptr_error_text = &char_error_text[0];
CString final_error_message = "";

With this code

m_definition_file.Open( m_definition_file_name, CFile::modeRead );
error_number = GetLastError();
format_message_return = FormatMessage(  0,              // dwFlags
                                        NULL,           // lpSousrce
                                        error_number,   // dwMessageID
                                        NULL,           // dwLanguageId
                                        ptr_error_text, // lpBuffer
                                        ERROR_MAX,      // nSize
                                        NULL     );     // Arguments
final_error_message = char_error_text;

The error number is 2 (two). char_error_text ends up with nothing. I am uncertain of the arguments for FormatMessage. The file name is forced to be incorrect and an error is expected.

Thanks for your time
If you work with telemetry, please check this bulletin board: http://www.bkelly.ws/irig_106/

Still looking for reason text

bkelly1322-Jun-13 12:17

bkelly13

22-Jun-13 12:17

I have yet to get a text based error code for opening a file. Here is the simplified code:

C++

m_definition_file_name = Select_Definition_File.GetPathName();
m_definition_file_name += "x";  // make the file name bad
m_definition_file.Open( m_definition_file_name, CFile::modeRead );

//  error_number = GetLastError();  // restore to verify error code is 2
get_error_message.GetErrorMessage( ptr_error_text, ERROR_MAX, NULL );
final_error_message = char_error_text;  // says no error

The Open method does not throw an exception. When GetLasError() is used, the error code is 2 (two).
The GetErrorMesssage yields No error returned, which is incorrect. The file could not be opened because it does not exist.

GetErrorMessage(...) is has three arguments about formatting the error message, but the error message is not an argument. I presume it gets the error message like GetLastError() does, but this appears incorrect.

How do I get a text string describing this error?

Thanks for your time
If you work with telemetry, please check this bulletin board: http://www.bkelly.ws/irig_106/

Re: Still looking for reason text

Richard MacCutchan23-Jun-13 0:51

Richard MacCutchan

23-Jun-13 0:51

I gave you a suggested solution at http://www.codeproject.com/Messages/4583835/Re-CFileException-discover-reasons.aspx[^], which should throw an exception whose value would be CFileException::fileNotFound (error code 2). Did you try it, and if so what result did you get?

In response to your comment about FormatMessage, you need to tell the function where to look for the mappings of error codes to messages thus:

C++

format_message_return = FormatMessage(FORMAT_MESSAGE_FROM_SYSTEM,  // dwFlags
                                        NULL,           // lpSousrce
                                        error_number,   // dwMessageID
                                        NULL,           // dwLanguageId
                                        ptr_error_text, // lpBuffer
                                        ERROR_MAX,      // nSize
                                        NULL     );     // Arguments

This is explained in full detail in the documentation[^].

Use the best guess

Re: Still looking for reason text

bkelly134-Jul-13 11:05

bkelly13

4-Jul-13 11:05

My apologies for no replying sooner. I followed your advice and now have that FormatMessage method working. Thank you.

Thanks for your time
If you work with telemetry, please check this bulletin board: http://www.bkelly.ws/irig_106/

Re: Still looking for reason text

Richard MacCutchan4-Jul-13 20:50

Richard MacCutchan

4-Jul-13 20:50

You're welcome.

Use the best guess

How to force C++ allocate memory from disk?

Falconapollo7-Jun-13 23:49

Falconapollo

7-Jun-13 23:49

I have thousands lines of C++ codes which work well on small text files, but crashes on huge text files (such as 2 GB size). Crash reason: app eats up memory.

Is it possible to allocate memory from disk? Because in most case, hard disk space is much bigger than physical memory. If I can borrow some space from hard disk for my app and return them back after use, then my app has little chance to crash.

Here are my design thoughts:

1.Create a temporary file for file mapping(CreateFileMapping, OpenFileMapping)
2.Force my app to allocate memory from the temporary file
3.Do some clean up work: CloseFileMapping and delete the temporary file

Because I have so much existing code, if my design thought is reasonable, I don't want to redesign my project.

I'm not sure if the design thought is possible to implement. Anybody can help me?

PS: I'm using Visual C++ 2010.

Re: How to force C++ allocate memory from disk?

MicroVirus11-Jun-13 0:13

MicroVirus

11-Jun-13 0:13

The most elegant approach is to use MapViewOfFile to only map a smaller piece of the file at any one time, one that does fit into your address space, and then shift the view by Unmap/Map-ing.
In conjunction with this, a way to slightly extend the limit of what can fit in your address space is to set the /LARGEADDRESSAWARE compiler switch, which can be found under the properties. This tells the compiler that you are aware of that 32 bits pointer can use the full range of 0 - 2^32-1, rather than only half that range 2^31-1. With this, you might be able to reach up to ~3GB, depending on system configuration and your application. However, this only slightly shifts the available memory.

Using the above approach, you map the piece of file that you want to use into your address space, and as soon as you are done with the current piece you map the next, etc.

Re: How to force C++ allocate memory from disk?

Falconapollo11-Jun-13 0:19

Falconapollo

11-Jun-13 0:19

thank you for your advice, i will have a try. Smile | :)

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