Re: Simple C to C++ - C / C++ / MFC Discussion Boards

Re: Simple C to C++

Chuck O'Toole14-Sep-11 14:32

Chuck O'Toole

14-Sep-11 14:32

In the C++ example, just what does

strcpy(msg,z_buf);

do to the string object? Assuming it compiles, are you clobbering the object?

I don't use the std:: classes much, but if this were MFC/ATL CString, the strcpy argument would use a typecasting to get a pointer to the internal buffer of CString (char *) which you are *NEVER ALLOWED TO OVERWRITE*. Yet the strcpy() call does exactly that.

I would imagine that std::string has a similar internal structure and would be very upset if you started overwriting its content.

Re: Simple C to C++

enhzflep14-Sep-11 16:21

enhzflep

14-Sep-11 16:21

The reason there's no upper limit on "i" in either of the for loops is that this would take more code - it would require a strlen be performed once before the loop in addition to checking to see if i is equal to this length. It's less clear to read and more prone to induce error during maintenance, but I believe it to be for this reason that the way the loop is exited with a break.

Not sure why you'd go the trouble of #defining NUL as 0x0.. It would be clearer if the already provided NULL was used (less code too, since there's only 4 references to 'NUL' - 4 cases of simply adding another 'L'. In any case, the executable code is identical - it is just the source-code that suffers from reduced readability, unlike the loop-terminating-condition check, which produces a smaller executable when done this way than the more readable alternative of checking the strlen first then using a terminarting condition of i<strlen(

can't see="" any="" reason="" for="" this="" to="" crash="" when="" executing="" the="" 'msg[i]="NUL'" statement,="" unless="" you're="" trying="" pass="" a="" string="" constant,="" rather="" than="" dynamically="" loaded="" created="" string.="" example,="" i="" can="" failing
<pre="">char *htmlStr = "<html>";
replace_html_delimiters(htmlStr);

while I can see this succeeding

char *htmlStr = "<html>";
char htmlStrCopy = strdup(htmlStr);
replace_html_delimiters(htmlStrCopy);
..
.. other actions on htmlStrCopy
..
free(htmlStrCopy);

Add to that the fact that the "char z_buf[4095]" statement isn't terminated with a ';' in either case and you have rather a problem, considering that the C function called with a string containing "" returns the same string. Studying the function, it appears to scan through a string, quitting upon end of string (0x0), while perplexingly, when it intercepts a '<' character it copies all of the text except for this character, then it appends the '<' explicitly. It's 5am here, and I can't think of a circumstance that the output sring would be different to the input string.

Re: Simple C to C++

Chuck O'Toole14-Sep-11 17:18

Chuck O'Toole

14-Sep-11 17:18

You're right in that the code looks odd but I think it was because the Code Project Editor messed it up. The OP was trying to replace the < character with the sequence ampersand-l-t, a sequence which if typed into this editor will yield a <, making the code look wrong. He's really making the string bigger with the replacements.

Re: Simple C to C++

Erudite_Eric14-Sep-11 20:41

Erudite_Eric

14-Sep-11 20:41

Software2007 wrote:
debugger would crash at msg[i] = nul in the c-like code

In that case msg is not a NULL terminated string.

How big do you expect msg to be, do you knwow?

If you do, you can add an additional check for not exceeding that length thus:

for(i=0; ; i++)  //Why no upper limit here?
   {
       if(msg[i]== NUL)
           break;
       if(i >  maxvmsglen)
           break;
...

The other likelyhood is that the code:

msg[i] = NUL;
    strcpy(z_buf,msg);
    strcat(z_buf,"<");
    strcat(z_buf,msg+i+1);//confusing me
    strcpy(msg,z_buf);

is mashing up the msg buffer and overflowing it. I have rarely seen such a horrible piece of code, what is it supposed to be doing?

==============================

Nothing to say.

Re: Simple C to C++

Richard MacCutchan14-Sep-11 22:14

Richard MacCutchan

14-Sep-11 22:14

This works:

C++

string msg = "<HEAD>strange</HEAD><body>beautiful</body>";
string::size_type index;
while ((index = msg.find('<')) != string::npos)
{
    msg = msg.replace(index, 1, "&lt;");
}

Remember that strings are immutable, they cannot be altered in-place, so each replace call returns the modified string, which you must use on the next iteration. Similarly expressions such as msg[i] = '\0'; will cause an access violation. See here[^] for all the lowdown on STL string types.

Unrequited desire is character building. OriginalGriff

Re: Simple C to C++

Orjan Westin15-Sep-11 1:38

Orjan Westin

15-Sep-11 1:38

Remember that strings are immutable

This is not true in standard C++. Did you think of C# or some pre-standard implementation of STL?

Re: Simple C to C++

Richard MacCutchan15-Sep-11 1:43

Richard MacCutchan

15-Sep-11 1:43

Cool Cow Orjan wrote:
Did you think of C#

Yep, my brain can only handle one language at a time. Frown | :(

However, the code still works.

Unrequited desire is character building. OriginalGriff

Re: Simple C to C++

Orjan Westin15-Sep-11 1:32

Orjan Westin

15-Sep-11 1:32

If you want to replace the character '<' in a string with, "<", it could be done quite simply in C++ like this:

C++

void replace_html_delimiters(std::string& str)
{
  std::string::size_type pos = str.find("<");
  while (std::string::npos != pos)
  {
    str.replace(pos, 1, "&lt;");
    pos = str.find("<", pos + 4);
  } 
}

Or if you want to cover the closing '>' as well:

C++

void replace_html_delimiters(std::string& str)
{
  std::string::size_type pos = str.find_first_of("<>");
  while (std::string::npos != pos)
  {
    if ('<' == str[pos])
      str.replace(pos, 1, "&lt;");
    else
      str.replace(pos, 1, "&gt;");
    pos = str.find_first_of("<>", pos + 4);
  } 
}

By the way, I assume that you had < in your code example, and that CodeProject converted it to < when you posted it? This can be avoided by escaping out the leading ampersand (& is also a reserved character in HTML, like < and >) like this: &lt;.

Otherwise, your C code would simply replace the character '<' with the character '<', with lots of copying back and forth.

C++

void replace_html_delimiters(char *msg)
{
  for(i=0; ; i++)
  {
    if(msg[i]== NUL)
      break;                 // End condition, so not needed in for statement
    if(msg[i]=='<')          
    {
      msg[i] = NUL;          // Replace found '<' with 0 to mark end of string
      strcpy(z_buf,msg);     // Copy string (up to the new end) to buffer
      strcat(z_buf,"<");     // Add string "<" to end of buffer 
      strcat(z_buf,msg+i+1); // Add remaining string to end of buffer)
      strcpy(msg,z_buf);     // Copy back to string. 
    }
  }
}

And that could be rewritten very effectively like this:

C++

void replace_html_delimiters(char *msg)
{
  // No need to do anything
}

Re: Simple C to C++

Stefan_Lang15-Sep-11 1:43

Stefan_Lang

15-Sep-11 1:43

First, the original code should compile and work for any C++ compiler. Almost any C code should, as long as your function declarations contain the full parameter list (this was not mandatory in C, but is in C++). If the function doesn't work as intended in C++, then it didn't in C either!

If your intention is to refactor the code into something that more resembles C++ coding standard, here's a few pointers:

1. Do not use #define for constants. C++ introduced the const keyword for that purpose and AFAIK ANSI C as well. #define always introduces a risk, as it replaces text without concern for the context, and therefore might break your code in places that it was not meant to affect. It's even worse when #defines are used in headers, making the replacement global.

2. Do not use magic numbers. Magic numbers are numeric or string literals that are used within the code to define array boundaries, values passed to functions, or limits used for loops. It's almost always better to instead define a constant, using a name that explains its purpose or use. There are multiple advantages of doing this: First, if you ever need to change the value you only need to change it in one place, no matter how often you used it, and no matter whether others used it in places that you don't even know of; Second, the name of the constant explains what it is, saving people the effort to somehow divine it from the context or (nonexistent) comments; Third, constant names are often easier to remember than the literals they represent. And intelligent editors will even remember these names for you.

3. Use std::string instead of C-style 0-terminated strings. They are sometimes more awkward to use, but they're fast and generally more safe. They also manage their own memory, so you don't need to allocate an arbitrarily sized buffer yourself, nor do you need to care about its deallocation. Also there are already plenty of functions available in the STL, either as member functions of std::string, or as generic functions found in algorithm:: (unfortunately though, none of them exactly reciprokes your function)

4. Be careful when using index values for std::string, or in fact any of the containers of the STL. For one, many functions in the STL require iterators, not index values; most of the time index values - if provided for a container - can be used to read (or write) an element, but nothing else! Second, checking for the end (or start) of a range is often not easily possible with index values, as you have noticed yourself. The usual method for iterating oover the contents of an STL container, and that includes strings, is by using iterators.

5. Don't use break, nor multiple return statements in a function: they are just as bad as goto in that they obscure the program flow and make it unneccesarily hard to understand the code. The best way to replace a break is putting the condition into the loop header. If some of the code needs to be skipped, store the condition in a variable that is used both in the loop header and in an if statement that encapsulates the part of the loop that needs to be skipped. The important part is that the condition(s) that end a loop should always be visible in the header, so anyone trying to analyze the program flow can immediately see whether a loop will be invoked at all, and for how long. (you already rightfully asked why there is no end condition in the C-style for loop!)

6. If you need a function that works on a STL object (in this case std::string), check for functions already in existance and learn how to use them. E. g. for std::string, check out http://www.cplusplus.com/reference/string/string/[^]

With all of the above (and more) in mind, your code should like something like this (not tested):

C++

#include <string>
#include <iostream>
const std::string LESSER_THAN_SIGN = "<";      // string literal -> use constant
const std::string LESSER_THAN_HTML = "&lt;";  // string literal again
const std::string GREATER_THAN_SIGN = ">";     // and another, extending your example
const std::string GREATER_THAN_HTML = "&gt;"; // again

/**
 * replaces all occurrences of some substring with another string
 * @param text     in/out   text to be worked on
 * @param from     in       substring to be replaced
 * @param to       in       string used as replacement
*/
void replace_all(std::string& text, const std::string& from, const std::string& to) {
   // Work your way through the entire text by repeatedly searching for 'from' string.
   // We will use the text position to store the current search position rather than
   // an iterator, because the string replacement might invalidate iterators!
   std::size_t textpos = 0;                        // the first position is 0, not 1
   std::size_t replaced_length = from.length();    // number of characters of the search string
   // keep searching for the string 'from' while an occurence can be found
   // find() will return std::string::npos as a result upon failure
   while ((textpos = string.find(from, textpos)) != std::string::npos) {
      // found an occurence of 'from' to replace
      // --> replace the substring starting at textpos with the new string 'to'
      text.replace(textpos, replaced_length, to);
   }
}

int main() {
   std::string text("<b>some fat text</b>");
   replace_all(text, LESSER_THAN_SIGN, LESSER_THAN_HTML);
   replace_all(text, GREATER_THAN_SIGN, GREATER_THAN_HTML);
   std::cout << text << std::endl;
   return 0;
}

Note: I used the JavaDoc style for commenting the function. This style is also used by Doxygen, a tool that like JavaDoc can automatically extract a full function level HTML documentation from these type of formatted comments. Even if you don't use DoxyGen, it is generally a good idea to define *some* standard for commenting each function.

Sorry this turned out rather longer than intended, but I hope you will appreciate it anyway Wink | ;)

Re: Simple C to C++

Richard MacCutchan15-Sep-11 1:47

Richard MacCutchan

15-Sep-11 1:47

Stefan_Lang wrote:
Sorry this turned out rather longer than

Don't apologise, it's an excellent analysis of the issues, and solution.

Unrequited desire is character building. OriginalGriff

Re: Simple C to C++

MicroVirus15-Sep-11 3:36

MicroVirus

15-Sep-11 3:36

Stefan_Lang wrote:
Sorry this turned out rather longer than intended, but I hope you will appreciate it anyway

Only ever apologise to yourself, for the time lost writing an excellent post Wink | ;)

MFC OpenGL Invalidate Flickering

appollosputnik14-Sep-11 6:19

appollosputnik

14-Sep-11 6:19

Dear Friends
I am wirting an application for drawing a rectangle on the screen using opengl and mfc. So I implemented the OnPaint function, OnDraw function is also giving the same problem. It's drawing fine. I want to implement pan, zoom, and rotate functionalities. Now everytime the mouse moves I am calling Invalidate() or otherwise I can call Invalidate() in the ::OnDraw function. Pan, zoom and rotate everything is happening but its heavily flickering. I have serached a lot and tried all means like return 1 in the OnEraseBackground() functio for WM_ERASEBACKGROUND etc. But I am getting still flickering . Please help getting rid of this problem. Check the code snippet below.

void CRevolutionProjView::OnPaint()
{
CPaintDC dc(this); // device context for painting
// TODO: Add your message handler code here
CRect RectAff;
GetClientRect(RectAff);
glClearColor ( 0.0f, 0.0f, 0.0f, 0.0f ) ;
glClear ( GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT ) ;
glPushMatrix( ) ;
glTranslatef(trans[0], trans[1], trans[2]);
glRotatef(rot[0], 1.0f, 0.0f, 0.0f);
glRotatef(rot[1], 0.0f, 1.0f, 0.0f);
drawcube();
glPopMatrix( ) ;
glFinish( ) ;
glFlush();
SwapBuffers(hDC);
Invalidate(false);
// Do not call CView::OnPaint() for painting messages
}

void CRevolutionProjView::OnMouseMove(UINT nFlags, CPoint point)
{
newP = point;
// TODO: Add your message handler code here and/or call default
int dx = oldP.x - newP.x;
int dy = newP.y - oldP.y;
switch(STATE)
{
case PAN:
{
trans[0] -= dx/100.0f;
trans[1] -= dy/100.0f;
// Invalidate();
}
break;
case ZOOM:
{
trans[2] -= (dx+dy) / 100.0f;
// Invalidate();
}
break;
case ROTATE:
{
rot[0] += (dy * 180.0f) / 500.0f;
rot[1] -= (dx * 180.0f) / 500.0f;
#define clamp(x) x = x > 360.0f ? x-360.0f : x < -360.0f ? x+=360.0f : x
clamp(rot[0]);
clamp(rot[1]);
// Invalidate();

}
break;
}

oldP = newP;

CView::OnMouseMove(nFlags, point);
}

Re: Flicker Free Drawing In MFC

Software_Developer14-Sep-11 7:32

Software_Developer

14-Sep-11 7:32

Flicker Free Drawing In MFC[^]

Re: MFC OpenGL Invalidate Flickering

Roger Allen27-Sep-11 6:23

Roger Allen

27-Sep-11 6:23

I would recommend that you create an off screen bitmap, render the open GL image to that and then StretchBlt or equivalent to the display.

I recently developed a 2d/3d graphing system that supported 3d by openGL and it worked well using this method.

If you vote me down, my score will only get lower

ShowHTMLDialog not working in Windows 7

doug2514-Sep-11 4:00

doug25

14-Sep-11 4:00

Hi,

I thought I'd cracked this problem but it seems that I was wrong. Although I know now that the problem lies with the operating system.

I want to display a web page in a window. I realized that this is possible with the ShowHTMLDialog function, however it only works in windows XP not windows 7. There is something else though: I can get a web page to display when I run the program directly in visual studio but not when I run it as a stand-alone application(in windows 7). So I think the problem is that some required dlls are being loaded when I run it in visual studio but not as standalone.

It seems that the only dll i need for ShowHTMLDialog is mshtml.dll but I'm not sure if other dlls with different versions from windows XP are being used.

What's going on when I run the program from visual studio that is different from running the program on it's own ? How do I get ShowHTMLDialog to work in windows 7 ?

(I'm not using MFC)

thanks,

Re: ShowHTMLDialog not working in Windows 7

Chris Meech14-Sep-11 6:07

Chris Meech

14-Sep-11 6:07

What kind of error are you getting? Not really sure what you mean when you say it only works on Windows XP, not Windows 7. You might be able to try using the dependancy walker application to find out what DLLs are needed by your application, thouhg. Smile | :)

Chris Meech
I am Canadian. [heard in a local bar]

In theory there is no difference between theory and practice. In practice there is. [Yogi Berra]

posting about Crystal Reports here is like discussing gay marriage on a catholic church’s website.[Nishant Sivakumar]

Re: ShowHTMLDialog not working in Windows 7

doug2514-Sep-11 7:39

doug25

14-Sep-11 7:39

the error is that the program crashes on a call to ShowHTMLDialog(only on windows 7) and no dialog window appears.

thanks, I will check out the dependancy walker

Re: ShowHTMLDialog not working in Windows 7

Chris Meech14-Sep-11 8:27

Chris Meech

14-Sep-11 8:27

Now that I checked here[^], I doubt that Dependancy Walker will help. You are going to have step through your code and find out which line of code is failing. My wild-ass guess would be that a call to GetProcAddress is probably not behaving as you expect it to.

Re: ShowHTMLDialog not working in Windows 7

doug2514-Sep-11 8:59

doug25

14-Sep-11 8:59

Ah, the problem is where I convert a char string to wide char string. I need to convert the url I want to display to a wide char string and if I leave that code out and just specify google as the url, the program works in windows 7.

I'm not sure what I'm doing wrong with the conversion ?

C++

char url[MAX_PATH];

_getcwd(url, MAX_PATH);
std::string file = url;
file += "\\Help.html\0";

OLECHAR* oleChar = NULL;
oleChar = (OLECHAR*)calloc(file.length(), sizeof(OLECHAR));
MultiByteToWideChar(CP_ACP, MB_PRECOMPOSED, file.c_str(), -1, oleChar, sizeof(OLECHAR)*file.length());

BSTR bstrURL = SysAllocString(oleChar);

index of member of a map?

zon_cpp14-Sep-11 3:16

zon_cpp

14-Sep-11 3:16

hi,
how do i know index of an iterator of a map?

map<int, int>::iterator it = mymap.find(3);

i want to know index of 'it' in mymap???

Zo.Naderi-Iran

Re: index of member of a map?

«_Superman_»14-Sep-11 3:31

«_Superman_»

14-Sep-11 3:31

You can increment a counter in a loop.
But why do you need this.
std::map always works on the key and so you must not use the index to perform any operations on the map.

Here is something you could do -

map<int, string> num;
int j = 0;
for (auto i = num.begin(); i != num.end(); ++i, ++j)
{
	if ((*i).first == 5)
		cout << j << endl;
}

Don't know if there is any other way to do this.

«_Superman_»
I love work. It gives me something to do between weekends.

Microsoft MVP (Visual C++)

Polymorphism in C

Re: index of member of a map?

C^hris L^osinger14-Sep-11 3:37

C^hris L^osinger

14-Sep-11 3:37

maps are not arranged in a simple linear order (they are trees), so there is no 'index' for an item.

image processing toolkits | batch image processing

WaitForSingleObject

john563213-Sep-11 23:41

john5632

13-Sep-11 23:41

int a[33*1024];
int _tmain(int argc, TCHAR* argv[], TCHAR* envp[])
{
	int nRetCode = 0;
	HANDLE hReadThread = NULL;	
	// initialize MFC and print and error on failure
	if (!AfxWinInit(::GetModuleHandle(NULL), NULL, ::GetCommandLine(), 0))
	{
		// TODO: change error code to suit your needs
		_tprintf(_T("Fatal Error: MFC initialization failed\n"));
		nRetCode = 1;
	}
	else
	{
		hReadThread = AfxBeginThread(ThreadWrite,0);
	}
	WaitForSingleObject(hReadThread,INFINITE);
	return nRetCode;
}

UINT ThreadWrite(LPVOID lParam)
{
	for(int i=0; i < 32*1024; i++)
	{
		a[i]=i;
		cout<<"Write:" << a[i];
	}
	return 1;
}

Why in above program,

WaitForSingleObject()

is not wating for thread comletion?

Re: WaitForSingleObject

CPallini14-Sep-11 0:12

CPallini

14-Sep-11 0:12

Because AfxBeginThread returns a pointer to a CWinThread object, not a thread handle (see "AfxBeginThread" at MSDN[^]).
You have to change from:

john5632 wrote:
hReadThread = AfxBeginThread(ThreadWrite,0);

to (error checks left to the reader)

C++

CWinThread * pWinThread = AfxBeginThread(ThreadWrite,0);
hReadThread = pWinThread->m_hThread;

If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler.
-- Alfonso the Wise, 13th Century King of Castile.

This is going on my arrogant assumptions. You may have a superb reason why I'm completely wrong.
-- Iain Clarke

[My articles]

Re: WaitForSingleObject

john563214-Sep-11 0:25

john5632

14-Sep-11 0:25

Thanks.

Use Ctrl+Left/Right to switch messages, Ctrl+Up/Down to switch threads, Ctrl+Shift+Left/Right to switch pages.