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Here[^] is a good example that show you how to access paralel port in any OS. I hope to help you ...
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Hi Folks... Having a hard time to figure out if we can call Rest Based Web Service API's in C++. Need to pass the secret Key to the Server and get back the response. Any idea or pointer or framework in C++ would be useful.
Any sample application will be useful.
Can it be done using sockets programming?
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raghunath sahoo wrote: Having a hard time to figure out if we can call Rest Based Web Service API's in C++
You can do just about anything in C++. Having said that, it might not be your easiest solution. Higher level languages tend to have better abstraction for certain things.
raghunath sahoo wrote: Can it be done using sockets programming?
Of course it can be done using socket programming, how exactly do you think web services work? Problem with developers that work at a high level is they don't seem to know about the magic that's happening in the background. Simple answer: the web works over sockets.
I just typed "REST C++" in google and got a bunch of results, why don't you try one of those?
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Thanks Albert... I had googled out earlier for the same...the links had no relevant information. The few pointers which are shown use may be other language framework to have the connection established.
I would rather just check out how win sock will be working.
Beacuse of the urgency just to write the code entirely in c++ and using any service or framework avalable or any one having worked in it... will be helpful to guide... as really am clueless.
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http://www.codeproject.com/Articles/3849/Simple-HTTP-Client-using-WININET
This link is helpful.
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Network stack goes something like this...
Socket->Raw Ethernet->IP->TCP->HTTP->Web Pages/Services
So basically, the sockets can be programmed with whatever language you want and everything else is layers that go above (or below) your base communication layer. Some languages offer higher abstraction so for example, you can get straight to web services without knowing anything about the other layers. Sometimes it's beneficial to keep things abstract to get things done quickly, but I'd personally recommend you at least know about the inner workings of things.
Here's a project[^] for C++ that deals with REST, it's from MS (I believe).
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Here is the test code:
http://codepad.org/zKTatneG[^]
struct Empty
{
};
struct JustLong
{
long data;
};
struct LongAndEmpty : public JustLong, private Empty
{
};
struct StringAndEmpty: public std::string, private Empty
{
};
int main()
{
cout << "Empty:" << sizeof(Empty) << endl;
cout << "JustLong:" << sizeof(JustLong) << endl;
cout << "String:" << sizeof(std::string) << endl;
cout << "LongAndEmpty:" << sizeof(LongAndEmpty) << endl;
cout << "StringAndEmpty:" << sizeof(StringAndEmpty) << endl;
return 0;
}
When you try it in other compiler (for example, see link above for codepad.org), results are correct, i.e. output looks like this:
Empty:1
JustLong:4
String:4
LongAndEmpty:4
StringAndEmpty:4
Now, when you try this in VC++ (2010), size of struct with std::string is always (debug and release) 4 more that size of just std::string. Any other structs/classes are of correct size, and only those with std::string are bigger than they should be. Am I missing something or this is MS bug?
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First it's not technically a bug unless it either doesn't work or doesn't meet the C++ spec. I don't think either of these things is the case.
Second it looks much more likely that StringAndEmpty is larger because it's derived from an already complex class the v-table for which is compiled into an external module. It's a guess but I reckon you've got an extra pointer in there to look up the pre-existing std::string vtable.
I have read a full explanation of the various sizes and formats of MSVC and other compilers minimal/empty/simple/complex structs and classes with and without virtual inheritance. I can neither remember all the details nor where I read it but I do remember that there were a lot more variations 4-byte, 8-byte, 12-byte, 16-byte, 20-byte 'headers' than I would ever have thought and much of the variation was within one type of compiler rather than between them. If I remember where that detailed research is I'll post a link.
"The secret of happiness is freedom, and the secret of freedom, courage."
Thucydides (B.C. 460-400)
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Well, consider the following struct:
struct JustString: public std::string
{
};
It has the same size as just std::string, so no, there is no extra pointer in VFT. The question I have is about Empty Base Class Optimization - size of empty base class should be reduced to zero in descendant if possible. Yes, it is not a requirement, only a suggestion in a standard. Problem is, I don't understand this: it works for non-MS compilers; in MS-compiler it works for all cases EXCEPT std:string. I will check later with VC++ 2012 to see if they made it work, but right now I have no other explanation than some problems with MS compiler. Or is there any compiler option specifically for this case that I don't know about?
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The example you give would not need an 'extra' pointer because it would only need the one to the external vtable as everything internal can be optimised away. So far only when you have an internal and an external base you have found the size increases. It's likely that even in that case the internal base could be optimised away but it isn't which may be a flaw in the Microsoft compiler or there may be some practical reason why that shouldn't be done. As I mentioned there are quite a number of combinations of single vs multiple inheritance, virtual and non-virtual bases, local and external bases, exported and non exported, complete and incomplete classes at the point of first declaration. Some optimisations such as empty base class removal will be available under some combinations and not others. For a comparison you could try the Clang compiler which is more C++11 compliant than MSVC and being open source has support forums where you can ask exactly why they did it a particular way. Some odd behaviour in this area in MSVC is more about backward compatability of the resulting binaries with older version of the compiler and of Windows than about mistakes in the current version.
"The secret of happiness is freedom, and the secret of freedom, courage."
Thucydides (B.C. 460-400)
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Kosta Cherry wrote: ...size of empty base class should be reduced to zero in descendant if possible.
The size of an empty class must not be zero to ensure that the addresses of two different objects will be different.
"One man's wage rise is another man's price increase." - Harold Wilson
"Fireproof doesn't mean the fire will never come. It means when the fire comes that you will be able to withstand it." - Michael Simmons
"Show me a community that obeys the Ten Commandments and I'll show you a less crowded prison system." - Anonymous
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Standalone one - yes. But we are talking here about descendants, where empty class/struct can be eliminated. This is called Empty Base Class Optimization (you can google for it).
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Kosta Cherry wrote: Am I missing something or this is MS bug?
The former.
As you have already googled this you understand that it is an optimization. Failure to optimize is not a "bug".
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Hello Friends
I am creating a MFC application in which I am saving a image from DC into bmp.I gave different effects on that image by using Gaussian Filter Formula by following this link
http://lodev.org/cgtutor/filtering.html[^]
I am setting image blur,embossed and etc by getting image pixels and then settign back.
Now, I want to add noise Effect to image based on some range(0-100)[if 10 then less particles in image,if 20 more particles and so on].
Using same Gaussian,I didnt get any idea to use any filter to give effect of Noise.
I tried my own formula also but it is not adding random particles to image.
Here is own way to set noise.I got pixels of Image and randomly change some pixels to black but tht was not producing noise in some continuous manner. I want it should apply in some manner.
int n = 0;
for(int x = 0; x < nWidth; ++x)
{
for(int y = 0; y < nHeight; ++y)
{
n++;
if(n > 9 + randomFactor)
{
n =0;
randomFactor += x; memDC.SetPixel(x,y,RGB(0,0,0));
}
}
}
I want to add noise randomly but in some continuous manner.
Any Ideas??
Regards
Y
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Well... I have to admit I have no idea of the Gaussian formula but I found a page with formulas which may help you:
IA State[^]
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Two things: You are not really adding noise, but just setting a pixel to black here and there.
The idea of noise is to modify all color components of all pixels by adding a random value (plus or minus). So, start off by using a random number generator like rand(), scale its return value to the amount of noise you want and add the outcome pixel by pixel. You may think of it as computing a noise image and adding that image to your original image.
If you want to refine that, don't use equally distributed random numbers, but gaussian distribution or others. And you may apply filterind (low-pass, higo-pass, etc) to the noise image before adding to modify the spectral distribution of noise.
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Hope you don't mind me posting this as a second question, but wanted to catch attention of anyone who is especially knowledgeable about timeGetTime as well.
Here is the simple code I'm using:
DWORD dwt=timeGetTime();
static DWORD dwt_was;
if(dwt_was!=0)
if(dwt<dwt_was)
dwt=dwt;
dwt_was=dwt;
Also - it's not the timer wrap around
I have just got it here set a break point on the dwt-dwt line and it shows:
dwt_was 54493247
dwt 54493246
How can timeGetTime() go backwards in time?
In case it is relevant this is on a Lenovo Thinkpad Edge e520
ALL FIVE TIMERS ARE INACCURATE - even when they are constrained to a single core:
GetSystemTimeAsFileTime(..)
timeGetTime()
GetTickCount()
QueryPerformanceCounter()
RTDSC()
They all jump back in time frequently on this machine. I have tested them all constrained to a single core.
The only thing I can think of is to try a best guess averaging process as described in this article but not convinced it will be much of an improvement or worth the work involved:
http://www.mindcontrol.org/~hplus/pc-timers.html[^]
Discussion here
http://devmaster.net/forums/topic/4670-need-help-with-queryperformancecounter-and-dual-processors/[^]
On the whole it works reasonably well most of the time. Only now and again get these glitches, they go back in time perhaps every second or two, by a ms or two - and with the metronome typically only playing a few notes per second at most, the chance of hitting a major glitch is fairly small.
I think that's the only reason that it is working as a functional metronome on my computer. It's actually pretty good, but wanted to make it more accurate than it is already.
Also this two discussion:
http://stackoverflow.com/questions/2904887/sub-millisecond-precision-timing-in-c-or-c[^]
There's also the KeQueryPerformanceCounter but I think that might just be for writers of Drivers - and with all the other ones not working don't know if it would fix the issue anyway.
There's the Windows timestamp project here:
href="http://windowstimestamp.com/description
[^]
but it seems to be work in progress, don't think you can actually use it in your apps yet??
If it can't be fixed, I'm also interested in any setting I can ask the user to set on their computer if they want to have the highest possible accuracy of timing? E.g. to switch off some power saving frequency adjusting feature or something?
The only other thing I can think of is to write to midi, convert the midi to audio, and play the audio - that is well timed, but not possible to do in real time.
(sorry forgot you can edit these posts - hence all those deleted extra messages below).
modified 15-Mar-13 3:39am.
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This is now solved.
First - it was a core switching issue. The code to confine to a single core has to be called in advance - I think possibly the thread has to sleep first before the system can assign it to a new core, at any rate doesn't work to just set it immediately before every time check and release it again afterwards. Also there was a bug in my code when checking to see if hte time was going backwards forgot to check if the previous time was recorded for the same thread, the dTimeWas should have been a thread local variable.
But - even after fixing all that, and tied to a single core, the timing was still inaccurate. It was monotonic but inaccurately timed, the reported time in ms sometimes passed more quickly than real time and sometimes passed more slowly.
I could check this by doing a real time recording to audio of the notes played by my app - which according to the high performance counter were played at equally spaced 100 ms intervals - but when you looked at the recording the actual recorded times were offset sometimes as much as 30 ms from the previously recorded note - had one recording that recorded an 80 ms note followed by a 110 ms note when the high precision timer said that they were all exactly 100 ms to within sub millisecond precision.
Finally fixed it by looking up the interrupt timer which is available to every user mode process as a volatile area of shared memory in a structure called KUSER_SHARED_DATA in the same location in the address space in every process.
This timer is highly accurate, not just sub-millisecond, it is also well sub-microsecond on my laptop anyway. It also records the time correctly. And there is almost no overhead involved in looking it up as it is only a memory look up, just like accessing any other area of memory.
Details here:
QueryPerformanceCounter-inaccurate-timing - SOLVED[^]
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Hi there,
I'm using the high performance counter for timing musical notes - and have run into a problem. It doesn't time them accurately. What should be a regular rhythm is irregular.
When I debug to find out what is happening, then the numbers returned by QueryPerformanceCounter(..) sometimes change direction - in this code below, if I put a break point on the
if(ddwt<ddwt_was)
ddwt=ddwt;
then it gets triggered.
As you see, I have requested that the thread runs on core 1 of dual core machine. I'm testing it on a laptop with two processors and two cores in each processor.
Is SetThreadAffinityMask(..) perhaps not enough to ensure that the thread runs on a single core? Or is there some other reason for it?
Is there any way to fix it so I can get sub-millisecond timing working accurately on any computer?
Thanks for your help.
LARGE_INTEGER HPT_PerformanceCount,HPT_PerformanceFrequency;
int found_HighPerformanceTimer_capabilities;
BOOL bHasHighPerformanceTimer;
double HighPerformanceTimer(void)
{
DWORD threadAffMask=SetThreadAffinityMask(GetCurrentThread(),1);
DWORD threadAffMaskNew=0;
if(found_HighPerformanceTimer_capabilities==0)
{
bHasHighPerformanceTimer=QueryPerformanceFrequency(&HPT_PerformanceFrequency);
found_HighPerformanceTimer_capabilities=1;
}
if(HPT_PerformanceFrequency.QuadPart==0)
{
SetThreadAffinityMask(GetCurrentThread(),threadAffMask );
return timeGetTime();
}
QueryPerformanceCounter(&HPT_PerformanceCount);
threadAffMaskNew=SetThreadAffinityMask(GetCurrentThread(),threadAffMask );
{
__int64 count=(__int64)(HPT_PerformanceCount.QuadPart);
__int64 freq=(__int64)(HPT_PerformanceFrequency.QuadPart);
double dcount=(double)count;
double dfreq=(double)freq;
double ddwt=dcount*1000.0/dfreq;
#ifdef _DEBUG
static double ddwt_was;
if(ddwt_was!=0)
if(ddwt<ddwt_was)
ddwt=ddwt;
ddwt_was=ddwt;
#endif
return ddwt;
}
}
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Just a hunch, but I believe it might be processor related.
Out-of-Order eXecution (OOX)
Code entering the pipeline isn't always executed sequentially. Most modern CPUs do it.
"It's true that hard work never killed anyone. But I figure, why take the chance." - Ronald Reagan
That's what machines are for.
Got a problem?
Sleep on it.
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