Re: [newbie] _lfind syntax problem

From: Victor Bazarov (v.Abazarov_at_comAcast.net)
Date: 12/23/04 

Date: Thu, 23 Dec 2004 11:57:45 -0500

Peter Schmitz wrote:
> this time, I want to do some binary searching.

Do you know what 'binary searching' means?

> Therefore I have declared the
> following:
>
> BYTE *buffer; //holds pointer to data to search in
> UINT bufferlen; //length in bytes of buffer
> BYTE *pattern; //holds pointer to pattern to search for
> UINT patternlen; //length of pattern in bytes
>
> Now, I've decided to use _lfind for this searching (I'm not using bsearch,

'_lfind' does NOT perform binary search. It performs a _linear_ search.

> because AFAIK I'd have to sort the buffer I search in - and as I normally
> search in rather small buffers this would decrease my speed significantly -
> or am I wrong?).

No, it's a valid reason.

> But somehow I don't get the correct syntax to call _lfind (perhaps because
> I'm a newbie to C). So, could someone show me how to call _lfind with the
> parameters from above?

     #include <iostream>
     using namespace std;
     #include <search.h>

     struct patternformatching {
         char const *pattern;
         int len;
     };

     int patternmatch(void const *pat, void const *str) {
         patternformatching const *p =
             reinterpret_cast<patternformatching const*>(pat);
         char const *s =
             reinterpret_cast<char const*>(str);

         return strncmp(s, p->pattern, p->len);
     }

     int main()
     {
         const char *pattern = "abc";
         int patternlen = 3;
         const char *buffer = "123abc123";
         int bufferlen = 9;

         patternformatching pat = { pattern, patternlen };
         unsigned searchlen = bufferlen - patternlen;
         const char * matched =
         (const char*) _lfind(&pat, buffer,
                             &searchlen, 1, patternmatch);
         if (matched) {
             cout << matched << endl;
         }
         else {
             cout << "didn't find\n";
         }
     }

This is a very convoluted way, of course. Use 'std::find_if', it should
be easier, actually.

Victor