C / C++ / MFC Discussion Boards

theallmightycpd27-Dec-07 5:26

27-Dec-07 5:26

Good day,

I'm having a little trouble and I'm not even sure if this can be done.

I am writing a program that calls an HTTP address in order to generate a javascript object that then needs to be read. The Web address generates a file that looks like this:

obj = new Object();
obj.var1='abc';
obj.var2='def';
obj.var3='geh';
obj.var4='ijk';

Currently, I am just calling that page and reading it in as a text stream. Doing it this way, I'm going to have to parse through the string and separate all the values manually.

Code is as follows:

static const char s_szAgent[] = "";

CString str;
CString strURL = "http://mysite.com/js.go?var=test";

try
{
CInternetSession objSession(s_szAgent);
CHttpFile* pFile = (CHttpFile*)objSession.OpenURL(strURL, 1,INTERNET_FLAG_TRANSFER_ASCII | INTERNET_FLAG_RELOAD | INTERNET_FLAG_DONT_CACHE);

// If open succeeded, read the file.
if (pFile)
{
CString strLine;
while (pFile->ReadString(strLine))
{
str+=strLine.Trim();
str+="\n";
}
pFile->Close();
delete pFile;
}
}
catch (CInternetException* pEx)
{
pEx->ReportError();
pEx->Delete();
}

Now my question is:
Is there a simpler way of doing this? Is there a way to just access that javascript object as a whole rather than just reading in a file string by string?

Re: Retrive JavaScript data from C++

Hakan Bulut28-Dec-07 7:25

Hakan Bulut

28-Dec-07 7:25

I guessing that, you talk about the ActiveX control usage. I have to been tried to ActiveX control to solve of the problem but I had no time to compile these codes:

 <br />
CString strResult;<br />
m_strResult = strResult;<br />
// TODO: Add your property handler here<br />
TCHAR* ch = strResult.GetBuffer(strResult.GetLenght());<br />
CStdioFile sf(("HTML1.html", CFile::ModeRead());<br />
while(sf.ReadString("strResulte"))<br />
{ <br />
	sprintf(string, "strResulte"); 	/* Read and write data object. */<br />
}<br />
CHttpFile* pFile;<br />
pFile->GetFileURL("c:\\Project\solution\res\html1.html");<br />
pFile->Open("\\res\html1.html", INTERNET_FLAG_RELOAD | INTERNET_FLAG_TRANSFER_ASCII , NULL);<br />
pFile->ReadString("strResulte"); /* "strResulte" is my JS data object to" */<br />
pFile->GetObject(&strResult);<br />
pFile->classCStdioFile.CreateObject(&sf);<br />
pFile->classCFile.IsDerivedFrom(CHTMLView*);	<br />
strResult.ReleaseBuffer();

Please, let me know if this idea can be helper.

Bitte tun Sie mir nicht antworten, wenn Sie nicht wissen, die Ursache des Problems wirklich oder nur als Antwort.

put try...catch... in a loop

followait27-Dec-07 4:03

followait

27-Dec-07 4:03

for (int i=0;i<largenum;++i) {<br="" mode="hold" />  try {} catch {}
}

Will the try...catch... hit the performance dramatically?

Re: put try...catch... in a loop

CPallini27-Dec-07 4:19

CPallini

27-Dec-07 4:19

I think you have to reformat your OP.
Use the escape sequence for the < operator (i.e. <).
Smile | :)

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.

[my articles]

Re: put try...catch... in a loop

David Crow27-Dec-07 4:21

David Crow

27-Dec-07 4:21

Have you performed a test with and without the try/catch code to see the difference?

"Normal is getting dressed in clothes that you buy for work and driving through traffic in a car that you are still paying for, in order to get to the job you need to pay for the clothes and the car and the house you leave vacant all day so you can afford to live in it." - Ellen Goodman

"To have a respect for ourselves guides our morals; to have deference for others governs our manners." - Laurence Sterne

Re: put try...catch... in a loop

followait27-Dec-07 4:30

followait

27-Dec-07 4:30

It works with sql server 2000.
But without the try...catch... the codes changed.
However, the try...catch... version is about 10% slow.
All because I insert strings to sql server 2000, and the string many contains singal quotation(s).

Re: put try...catch... in a loop

Maxwell Chen27-Dec-07 4:28

Maxwell Chen

27-Dec-07 4:28

You can have VC++ generate an ASM listing file.

Maxwell Chen

why visual studio does not optimize constructor in this case

George_George27-Dec-07 2:24

George_George

27-Dec-07 2:24

Hello everyone,

Why visual studio does not optimize constructor in this case? I do not understand what the MSDN mentioned,

if use different named object, compiler can not optimize. Why?

http://msdn2.microsoft.com/en-us/library/ms364057(vs.80).aspx

class RVO
{
public:
       
            RVO(){printf("I am in constructor\n");}
            RVO (const RVO& c_RVO) {printf ("I am in copy constructor\n");}
            int mem_var;       
};
RVO MyMethod (int i)
{
            RVO rvo;
            rvo.mem_var = i;
      if (rvo.mem_var == 10)
         return (RVO());
            return (rvo); 
}
int main()
{
            RVO rvo;
            rvo=MyMethod(5);
}

Output is,

I am in constructor
I am in constructor
I am in copy constructor

My expected output is,

I am in constructor
I am in constructor

thanks in advance,
George

Re: why visual studio does not optimize constructor in this case

Maximilien27-Dec-07 4:03

Maximilien

27-Dec-07 4:03

does this limitation applies in your case ?

Multiple return paths (even if the same named object is returned on all paths) with EH states introduced.

There are 2 return paths in your MyMethod.

Maximilien Lincourt
Your Head A Splode - Strong Bad

Re: why visual studio does not optimize constructor in this case

George_George27-Dec-07 4:10

George_George

27-Dec-07 4:10

Thanks Maximilien,

What means EH states?

I do not know why diferent execution path will disable compiler from optimization. In the sample, there are two execution paths to return,

1. return (RVO());

In case (1), compiler could optimize by saving the creating of the temporary object and assign to the extern rvo object directly.

2. return (rvo);

In this case (2), compiler could optimize by not creating the temporary object for the return value, and assign the inner rvo to outter rvo directly.

Why compiler can not optimize it?

regards,
George

Re: why visual studio does not optimize constructor in this case

Maxwell Chen27-Dec-07 4:20

Maxwell Chen

27-Dec-07 4:20

George_George wrote:
What means EH states?

The exception handling state.

Maxwell Chen

Re: why visual studio does not optimize constructor in this case

George_George27-Dec-07 16:49

George_George

27-Dec-07 16:49

Thanks Maxwell,

I have provided my perpective below why the compiler should be able to optimize the code, and it is appreciated if you could review and comment.

regards,
George

Re: why visual studio does not optimize constructor in this case

Maxwell Chen27-Dec-07 4:11

Maxwell Chen

27-Dec-07 4:11

"Named Return Value Optimization" is mainly Stan Lippman's work. As you have read that there are three exceptions which NRVO do not take place.

Different paths returning different named objects. 
Multiple return paths (even if the same named object is returned on all paths) with EH states introduced. 
The named object returned is referenced in an inline asm block.

Let's see your example (example 7 in MSDN). In function RVO MyMethod(int i), there are two return paths (see below). They are different intermediate object names. The compiler can not simplify these two return path into one.

RVO MyMethod (int i){
    RVO rvo;
    rvo.mem_var = i;
    if (rvo.mem_var == 10)
        return (RVO()); // Path (1).
    return (rvo);       // Path (2).
}

Maxwell Chen

Re: why visual studio does not optimize constructor in this case

George_George27-Dec-07 16:36

George_George

27-Dec-07 16:36

Thanks Maxwell,

I can understand the real path for execution could only be decided at runtime. Smile | :)

But I do not know why which named variable/return path matters the optimization -- the optimization only happens when the function returns and compiler only needs to insert optimization code at the place where there is a return statement -- if there are multiple returns, the compiler could put multiple optimization into multiple return statement.

I think no matter which one will return, either rvo or RVO(), the return value is a temporary obejct, and compiler could optimize it by using assignment operator on the outside rvo object instance directly without creating the temporary object, right?

Why the named variable/return path matters? Could you provide more information about your analysis please?

regards,
George

Re: why visual studio does not optimize constructor in this case

Maxwell Chen27-Dec-07 17:56

Maxwell Chen

27-Dec-07 17:56

George_George wrote:
But I do not know why which named variable/return path matters the optimization

The term "optimization" refers to two aspects: (1) efficiency, and (2) code size.
(1) The efficiency concept: Just like finding the shortest path.
(2) The code size issue: If many return paths can be simplified, concluded, and compacted into one single return path, the code size will be smaller. And maybe it would be more efficient.

Maxwell Chen

Re: why visual studio does not optimize constructor in this case

George_George27-Dec-07 18:15

George_George

27-Dec-07 18:15

Thanks Maxwell,

I think you mean there is room for compiler to optimize the speed of the code, but considering the binary size will be larger, the code can not be optimized, right?

But I am confused that I assign the /O2 (optimize for max speed) and it should work and does not consider the resulting binary size -- which is the purpose of /O1 (optimize for small size). Any comments?

regards,
George

Re: why visual studio does not optimize constructor in this case

Sarath C27-Dec-07 4:55

Sarath C

27-Dec-07 4:55

George_George wrote:
RVO rvo;
rvo.mem_var = i;
if (rvo.mem_var == 10)
return (RVO());
return (rvo);

IMHO, In this case the optimization will be difficult and sometimes useless. That may be the reason the code goes untouched.

Suppose the return value pass by hidden reference,as per the article,

1. If value of i == 10, it have to construct/copy the return value once again after initialization as the newly cosntructed object depends on another location of memory. which gives no advantage on optimization

2.As per the article, the NRVO is basically on workes with single return objects.

In the following case, the optimization dint work.

RVO rvo;<br />
	<br />
	if ( 11 == 10)<br />
		return (RVO());<br />
	rvo.mem_var = i;

return (rvo);

In the following case compiler damn sure that

if ( 11 == 10)<br />
    return (RVO());

The above case will never works, so NRVO can be applied but still it's missing I believe.

Anyway I'm not so expert in optimization related things, please share you view points.

-Sarath.
"Great hopes make everything great possible" - Benjamin Franklin

My blog - Sharing My Thoughts, An Article - Understanding Statepattern

Re: why visual studio does not optimize constructor in this case

George_George27-Dec-07 16:42

George_George

27-Dec-07 16:42

Thanks for sharing your perpective, Sarath!

Two more comments,

1. I do not quite understand why you think below in the case there is no room to optimize? Could you provide more description please?

Sarath. wrote:
1. If value of i == 10, it have to construct/copy the return value once again after initialization as the newly cosntructed object depends on another location of memory. which gives no advantage on optimization

2. here is my perpective mentioned before, please feel free to comment and correct. Smile | :)

--------------------
I do not know why which rvo instance will return matters. I think no matter which one will return, either rvo or RVO(), the return value is a temporary obejct, and compiler could optimize it by using assignment operator on the outside rvo object instance directly without creating the temporary object, right?

Why the path matters? Could you provide more information about your analysis please?
--------------------

regards,
George

Re: why visual studio does not optimize constructor in this case

Sarath C27-Dec-07 19:15

Sarath C

27-Dec-07 19:15

George_George wrote:
1. I do not quite understand why you think below in the case there is no room to optimize? Could you provide more description please?

Sarath. wrote:
1. If value of i == 10, it have to construct/copy the return value once again after initialization as the newly cosntructed object depends on another location of memory. which gives no advantage on optimization

I was talking based on the article.

Please check Hidden argument with/without NRVO[^]

-Sarath.
"Great hopes make everything great possible" - Benjamin Franklin

My blog - Sharing My Thoughts, An Article - Understanding Statepattern

can anybody explain me the reason for this for loop

Deepu Antony27-Dec-07 2:06

Deepu Antony

27-Dec-07 2:06

i have a for loop like this

for(int i=0;i=3;i++)
{
cout<<"hello";
}

Ans :it works infinite times

can anybody explain me the reason for this for loop

Re: can anybody explain me the reason for this for loop

CPallini27-Dec-07 2:16

CPallini

27-Dec-07 2:16

Hint:
the expression

i=3;

evaluates to 3, i.e. non-zero.
Smile | :)

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.

[my articles]

Re: can anybody explain me the reason for this for loop

PJ Arends27-Dec-07 2:17

PJ Arends

27-Dec-07 2:17

Deepu Antony wrote:
i=3;

try i==3;, or better yet 3==i;

You may be right
I may be crazy
-- Billy Joel --

Within you lies the power for good - Use it!

Re: can anybody explain me the reason for this for loop

David Crow27-Dec-07 2:17

David Crow

27-Dec-07 2:17

It loops infinitely because i=3 (the conditional part of the for() loop) always evaluates to non-zero.

Re: can anybody explain me the reason for this for loop

Deepu Antony27-Dec-07 3:03

Deepu Antony

27-Dec-07 3:03

thanks a lot

How can i make some EDIT line read only and leave the color of the control in WITHE color ?

Yanshof27-Dec-07 1:50

Yanshof

27-Dec-07 1:50

Hi All,

I want to change some edit line to be read only but when i change the control properties i see that the control is in gray color -

I want that the control will stay in withe color - how can i do it ?

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