(C++) Getting std::find_if working with std::string and string.compare() | Tech Off

RichardRudek
So what do you expect for nothin'... :P

I was wondering whether anyone has been able to get find_if working when using a vector of string, searching for a paritcualr string.

[I've documented what I've found so far on my blog], and would be interested if any of you have found a solution - although it's just an academic one, now.

Thanks.

Sven Groot
My name has 9 letters. Coincidence? I think not...

I'm not entirely sure why you're using std::find_if in the first place. It seems like all you're doing is finding a string value in the list, which regular std::find can do.

Using string::compare as the predicate for find_if is never going to work because it returns an int which is zero when the strings are equal rather than a boolean which is nonzero (true) when the strings are equal.

RichardRudek
So what do you expect for nothin'... :P

Sven Groot wrote:
I'm not entirely sure why you're using std::find_if in the first place. It seems like all you're doing is finding a string value in the list, which regular std::find can do.

I'm obviously doing something wrong, then. Cause this:

RIter = std::find(v1.begin(), v1.end(), string("pearly") );

gives this result:

error C2784: 'bool std::operator ==(const std::vector<_Ty,_Alloc> &,const std::vector<_Ty,_Alloc> &)' :
 could not deduce template argument for 'const std::vector<_Ty,_Alloc> &' from 'std::basic_string<_Elem,_Traits,_Ax>'
 C:\Program Files\Microsoft Visual Studio 8\VC\include\algorithm	40

Sven Groot wrote:
Using string::compare as the predicate for find_if is never going to work because it returns an int which is zero when the strings are equal rather than a boolean which is nonzero (true) when the strings are equal.

Yeah, I originally had a not1() prefixing all of that, but have left it out trying to figure out why it's failing. Well, I know why it's failing, but whether it can be resolved.

The point of this exercise is not just to solve this particular example, but to learn the appropriate 'generic' practice. It seems basic_string doesn't have all the bits needed by the algorithm and functional libs - or at least I'm doing something stupid.

Sven Groot
My name has 9 letters. Coincidence? I think not...

I think that's because you're not #including the <string> header so you're missing half of the basic_string class. <cstring> != <string>.

RichardRudek
So what do you expect for nothin'... :P

Sven Groot wrote:
I think that's because you're not #including the <string> header so you're missing half of the basic_string class. <cstring> != <string>.

Yeap. Thanks Sven Big Smile

OK, so we've sorted that bit of stupidity. But the find_if/compare predicate still doesn't work. Same problem about ref of ref.

Is this solvable, I wonder. ?

Sven Groot
My name has 9 letters. Coincidence? I think not...

I don't think so. The problem is that the second parameter you're trying to bind to is already a reference and the bind2nd function tries to take a reference to that, which doesn't work. Plus then there's the problem with the compare return type which I mentioned earlier.