C / C++ / MFC

pasztorpisti23-Aug-12 4:49

23-Aug-12 4:49

Two optimization tricks:
1. You store the possible values (A, B, and C, ...) in a sorted array and you search your string in that array with binary halving. Alternatively you can store A,B,C in one of these: map/hashmap/search tree.
2. If you opt for using == and/or != with if/else then you can speed up these operations for strings by storing the hash value for each string. When you compare two strings you first compare the hash values. If the hash is different then you have your result immediately (false for == and true for !=). If the hash for the strings is different then you have to perform the actual comparison on the strings. I usually write a special string class that contains the hash as well. It has the drawback that the hash must be updated before comparisons if the string has been modified since the last hash calculations. Sometimes purely written old legacy code can be tweaked very well with this trick. Use djb2 to hash your strings, for unicode use utf8: http://www.cse.yorku.ca/~oz/hash.html[^]

EDIT: Just noticed my answer isn't exactly the what you are searching for, but I think there is no fine solution to your problem. This problem is similar to the typical factory patterns that are used to instantiate a specific type by name:

C++

template <typename T>
class StringSwitch
{
public:
	void SetInstance(T* instance)
	{
		m_Instance = instance;
	}
	void RegisterHandler(const std::string& s, void (T::*handler)())
	{
		m_SwitchTable[s] = handler;
	}
	bool PerformOperation(const std::string& s)
	{
		auto it = m_SwitchTable.find(s);
		if (it == m_SwitchTable.end())
			return false;
		(m_Instance->*(it->second))();
		return true;
	}
private:
	std::map<std::string,void(T::*)()> m_SwitchTable;
	T* m_Instance;
};


class BlahBlah
{
public:
	BlahBlah()
	{
		m_SwitchTable1.SetInstance(this);
		m_SwitchTable1.RegisterHandler("A", &BlahBlah::StringA);
		m_SwitchTable1.RegisterHandler("B", &BlahBlah::StringB);
		m_SwitchTable1.RegisterHandler("C", &BlahBlah::StringC);
	}

	void StringA()
	{
		printf("%s\n", __FUNCTION__);
	}
	void StringB()
	{
		printf("%s\n", __FUNCTION__);
	}
	void StringC()
	{
		printf("%s\n", __FUNCTION__);
	}

	void Run()
	{
		m_SwitchTable1.PerformOperation("B");
	}

private:
	StringSwitch<BlahBlah> m_SwitchTable1;
};

int main()
{
	BlahBlah b;
	b.Run();
	return 0;
}

Your refactorized if/else is inside BlahBlah::Run()

modified 23-Aug-12 11:09am.

Mihai Vrinceanu23-Aug-12 5:41

Mihai Vrinceanu

23-Aug-12 5:41

You can choose to store strings in buffers of length 4*n. That way you can compare two DWORD vectors. It will be case sensitive, but faster than strcmp. You can also use switch on the first DWORD, but !!!ONLY!!! if no two strings share the same 4 bytes at the begining.

Also, Pascal strings. Smile | :)

_Flaviu23-Aug-12 8:36

_Flaviu

23-Aug-12 8:36

Triky solution ! Got my 5 !

David Crow23-Aug-12 5:53

David Crow

23-Aug-12 5:53

A minor optimization would be to order your comparisons from most-likely-to-match down to least-likely-to-match. That way, your if test block is exited as soon as possible.

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jschell23-Aug-12 8:22

jschell

23-Aug-12 8:22

Maximilien wrote:
t is there a better way to do cascading If comparisons on strings

Where "better" means what?

If you just don't like looking at the code then you could do code generation.

If there is a actual profiled performance problem traced to this then you can used collected data to order the comparisons with most used first and least used last. Depending on the number of strings, and the data in the strings other optimizations are possible.

One solution again dependent on data and usage is to parse the input, when first received, into a value such as an enumeration and only use that in the rest of the code.

If there is a lot of churn with these then generation can still help but dynamic collections might solve that, with care. However such solutions might not be as performant and add some level of complexity.

_Flaviu23-Aug-12 8:33

_Flaviu

23-Aug-12 8:33

I give you a little solution (MFC way):

C++

CStringList List;
List.AddTail(A);
List.AddTail(B);
List.AddTail(C);
List.AddTail(D);
....
// A,b, .. is also strings

if(NULL != List.Find(string))
{
    // we have the string, so you can do whatever you want
}

CPallini23-Aug-12 22:54

23-Aug-12 22:54

What do you mean with 'better'?
If you mean 'more good looking', then I suppose your code becomes 'ugly' only if some of your // do someting for ... is long (I mean, switch, in my opinion, isn't much better than the if-chain).

A completely different approach would be transforming the // do something for .. pieces of code into functions (or function objects) and then use a std::map to map the strings to the function pointers (or function objects).

Veni, vidi, vici.

image processing toolkits | batch image processing

C^hris L^osinger24-Aug-12 1:20

C^hris L^osinger

24-Aug-12 1:20

1. for each string in your list, register a domain name: A.com, B.com, C.com, etc..
2. on each site, install a web service that will return the code to be used in the "// do something for A" and "// do something for B", sections.
3. your code then calls out to the web service hosted at: "http://" + string + ".com"
4. it will receive the code it needs to execute

code = getCodeFrom("http://" + string + ".com");
exec(code);

it's up to you which language you use for the code, but you will obviously need an interpreter of some kind.

CPallini24-Aug-12 1:53

24-Aug-12 1:53

I'll try it. Big Grin | :-D

Veni, vidi, vici.

pasztorpisti24-Aug-12 2:20

24-Aug-12 2:20

+5. Absolute professional approach, however you forgot to mention the use of some useful frameworks/middlewares. Smile | :)

Maximilien24-Aug-12 4:04

Maximilien

24-Aug-12 4:04

That would freak out my code-reviewer !!!

Watched code never compiles.

run bat file using ShellExecute

bkelly1326-Aug-12 15:55

bkelly13

26-Aug-12 15:55

Can you reduce the scope of your problem space?
By that I mean: The broad example presumes that the input can be essentially anything.

Change that such that the input can begin with only certain strings or must contain certain keywords. Then you can divide the code up into different sections depending on how the input string can be grouped.

Thanks for your time

manju 323-Aug-12 2:16

manju 3

23-Aug-12 2:16

Hi all,
How can i run the bat file using SghellExecute.I am trying with the below code.

ShellExecute(NULL,_T("open"),_T("cmd.exe"),_T("/C Test.bat"),0,SW_SHOW);

Note : Test.bat file path is "C:\Test.bat"
I am unable to run the bat file.Am i doing anything wrong..??

But when i manually click on Test.bat with the mouse,The bat file executes fine.

Thanks in Advance
Manju

Re: run bat file using ShellExecute

Chris Meech23-Aug-12 2:20

Chris Meech

23-Aug-12 2:20

Try the following.

ShellExecute(NULL,_T("open"),_T("cmd.exe"),_T("/C C:\\Test.bat"),0,SW_SHOW);

I suspect that when cmd.exe is run, it is unable to find the file Test.bat. Smile | :)

Chris Meech
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Re: run bat file using ShellExecute

pasztorpisti23-Aug-12 3:07

Write to Text file using fprintf

23-Aug-12 3:07

Instead of

C++

ShellExecute(NULL,_T("open"),_T("cmd.exe"),_T("/C Test.bat"),0,SW_SHOW);

use either this:

C++

ShellExecute(NULL, _T("open"), _T("cmd.exe"), _T("/C C:\\Test.bat"), NULL, SW_SHOW);

or this:

C++

ShellExecute(NULL, _T("open"), _T("cmd.exe"), _T("/C Test.bat"), _T("C:\\"), SW_SHOW);

Note that the two solutions are not equivalent. In the second solution the current directory of your batch file will be C:\ while in the first case cmd.exe will inherit the current directory of the program from which you call ShellExecute().

manju 323-Aug-12 1:06

manju 3

23-Aug-12 1:06

Hi all,
I am trying to write one string to a file.But i am getting only one character
saved in my Text.txt file.Output text file contains only "a" in it.
How can i get whole string saved in my text file.
Here is the code i am trying:

FILE *fptr;
CString Text;
Text = "asdasdasdasd";
fptr = fopen("D:\\Test.txt","w+");
if(fptr== NULL)
   exit(1);
fprintf(fptr ,"%s",Text);
fclose(fptr);

If i write it as ""asdasdasdasd"" instead of passing the CString,it writes in the text file
fprintf(fptr ,"%s",""asdasdasdasd"");

Can anyone help me,where i am going wrong.

Thanks
Manju

Richard MacCutchan23-Aug-12 1:56

Richard MacCutchan

23-Aug-12 1:56

I suspect your CString may be defaulting to Unicode (check your project settings), so it appears as though you have only written a single character. Try using CStringA and see what happens.

One of these days I'm going to think of a really clever signature.

CPallini23-Aug-12 22:55

23-Aug-12 22:55

I suspect you are right.

Veni, vidi, vici.

Richard MacCutchan23-Aug-12 23:47

Richard MacCutchan

23-Aug-12 23:47

No, I think pasztorpisti is right, the string needs to be cast to LPCTSTR to get the content.

One of these days I'm going to think of a really clever signature.

CPallini25-Aug-12 7:25

25-Aug-12 7:25

Now I'm quite confident you are right. Smile | :)

Veni, vidi, vici.

Richard MacCutchan25-Aug-12 7:29

Richard MacCutchan

25-Aug-12 7:29

I hope your confidence is not misplaced.

One of these days I'm going to think of a really clever signature.

pasztorpisti23-Aug-12 1:59