Searching an Array for multiple items at specified locations

[mcbrune]

I have a program that currently has ALOT of if/else if statements searching a char array for specified elements at known locations. For example, I am looking for chars 'a' and 'b' at location 0, 3 or 4, 6. I thought of using a case statement, but because of the two values, I didn't think this work. Any other hints or is if/else the only way?

Thanks in advance!

 

[PerFnurt]

Well, you could do a switch on the variable you check the most values on.

Like,

char ch = charArray[location];
switch(location)
{
  case 0:
  case 3:
  case 4:
  case 6:
    if(ch == 'a' || ch == 'b')
    {
       ...
    };break;
  case 2:
  case 5:
    if(ch == 'c' || ch == 'd')
    {
       ...
    };break;
}
but if you really have a lot and all matches should result in the same handling, you could use a map, for example:
[code]
#include <map>
#include <string>
typedef std::map<int,std::string> Lookup;
...
{
  Lookup lookup;
  lookup[0]= "ab";
  lookup[2]= "cd";
  lookup[3]= "ab";
  lookup[4]= "ab";
  lookup[5]= "cd";
  lookup[6]= "ab";
}

// Then in the loop you'd check the contents of the map
// (It's assumed lookup has been passed to the function)
{
  ...
  Lookup::const_iterator i = lookup.find(location);
  if (i!=lookup.end())
  {
    if ((*i).find(charArray[location])!=std::string::npos)
    {
      // Do something
    }
  }
  ...
}

/Per

_{"It was a work of art, flawless, sublime. A triumph equaled only by its monumental failure."}

 

[PerFnurt]

Another way more using the ++ part of C++ can be useful if the charArray is really big and you have a lot of characters to test against, and/or you want to modify it without dig into the (growing?) if..else statement.

Make a small framework that lets you do the checking in a generic fashion, at one point you define what's done and when, while the checking itself is quite generic.

// A Doer is a class that does something :-)
class Doer
{
	virtual ~Doer() {}
	virtual void doSomething()=0;
};

class DoThis : public Doer
{
	virtual ~DoThis() {}
	virtual void doSomething() { ... }
};

class DoThat : public Doer
{
	virtual ~DoThat() {}
	virtual void doSomething() { ... }
};

// Map a doer to a string
typedef std::pair<std::string, Doer*> StringDoer;
// Map StringDoers to locations
typedef std::map<int, StringDoer> Lookup;

	// At some point define what location & char relate to a certain Doer
	...
	Lookup lookup;
	DoThis doThis;
	DoThat doThat;

	lookup[0] = StringDoer("ab", &doThis);
	lookup[3] = StringDoer("ab", &doThis);
	lookup[4] = StringDoer("ab", &doThis);
	lookup[6] = StringDoer("ab", &doThis);

	lookup[2] = StringDoer("cd", &doThat);
	lookup[5] = StringDoer("cd", &doThat);
	...
	// The checking is unaffected by the size of things...
	Lookup::const_iterator i = lookup.find(location);
	if (i!=lookup.end())
	{
		if ((*i).second.first.find(charArray[location])!=std::string::npos)
		{
			// Call the doer for this location/char combination
			(*i).second.second->doSomething();      
		}
	}

/Per

_{"It was a work of art, flawless, sublime. A triumph equaled only by its monumental failure."}

 

[sfi]

Hows about this...
(I've been doing PERL lately so forgive the syntax errors)

boolean find( char *theString)
{
int size = 0;
char *temp = theString;
int nChars = 2;
char theChars[] = ('a', 'b');
int nSpots = 2;
int theSpots[][nChars] = ((0,3), (4,6));

while (*temp++)
++size;

for (i=0; i<nSpots; ++i) {
found = 0;
for (j=0; j<nChars; ++j) {
if (theSpots[j] >= size)
break;
if (theString[ theSpots[j]]==theChars[j])
++found;
}
if (found==nChars)
return TRUE;
}

return FALSE;
}