C / C++ / MFC

cp9876 wrote:

You are right, for a few cases the difference may be negligible.

cp9876 wrote:

My understanding is that the switch statement can be optimized to O(log(N)) operations (using a tree type of search), whereas the simple cascaded if's will be O(N) operations. Obviously these could be the same but the compiler knows it can optimize a switch statement as the cases are all integer constants. I'd be interested to know the results if anyone can be bothered to do some test cases and analyse the code. It may be that the way the case statements are tested using less than operations is indicative that it would use a tree search for more cases (instead of the simple comparisons in the if construct).

CPallini wrote:

In fact there is no difference at all, in the code snippet shown

Eranga Thennakoon wrote:

Is there any special advantage use of switch-case combination than if() condition.

// MyClass.h
enum STATUS { St_A, St_B, St_C };
// ...
MyClass::STATUS MyClass::GetStatus();
// ...

// MyClass.cpp
switch(GetStatus())
{
case MyClass::St_A:
  // ...
case MyClass::St_B:
  // ...
default:
  // Error.
}

Eranga Thennakoon wrote:

if(strString.at(i) == ' ')
{
iSpace ++;
}
if(strString.at(i) == '\t')
{
iTabs ++;
}
if(strString.at(i) == '\r')
{
iRet ++;
}

int nCount = std::count(strString.begin(), strString.end(), ' ');
nCount += std::count(strString.begin(), strString.end(), '\r');
nCount += std::count(strString.begin(), strString.end(), '\t');

jhwurmbach wrote:

But that definitely is the slowest alternative...

#include <fstream><br />
#include <string><br />
#include<iostream><br />
using namespace std;<br />
<br />
int main()<br />
{<br />
	string str;<br />
<br />
	ifstream myFile("ap1.txt");<br />
	if(! myFile)<br />
	{<br />
		cout<<"Error!"<<endl;<br />
		return -1;<br />
	}<br />
	while(! myFile.eof())<br />
	{<br />
		<br />
			getline(myFile, str);<br />
			str;	<br />
			cout<<str<<endl;<br />
	<br />
	}<br />
	myFile.close();<br />
	return 0;<br />
}

Read a Line;
Does it start with Value = ?
Yes...
    Does it have Integer32 next?
    Yes...
        Grab the -44 part, and keep it somehow. A list, email it to your best friend, whatever you want.
No...
    Move on to the next line!

Variable = .iso.org.dod.internet.private.enterprises.9.9.273.1.3.1.1.3.1.8.105.118.116.108.95.97.112.49.0.2.45.4.155.81<br />
Value    = Integer32 -39<br />
<br />
Variable = .iso.org.dod.internet.private.enterprises.9.9.273.1.3.1.1.3.1.8.105.118.116.108.95.97.112.49.0.32.166.80.182.220<br />
Value    = Integer32 -39<br />
<br />
End of MIB subtree.<br />
<br />