Question

I want to make sure a string has at least one alpha. Simple:

if ( find_if(field_name.begin(), field_name.end(), isalpha) == field_name.end() )

But I want to use a locale. I know I can easily write a separate function but I’d prefer to use it within the find_if. I.e.,

include <locale>

std::locale loc;

if ( find_if(field_name.begin(), field_name.end(), isalpha(*this_iterator,loc) == field_name.end() )

Question: Is there someway to make this_iterator refer to the then-current iterator?

Answer 1

In C++11 you can do this with a lambda as Timo suggests, or with std::bind(), as in std::bind(isalpha, std::placeholders::_1, loc).

Pre-C++11, you can use std::bind2nd() instead. This gets a bit complicated though, as it requires a unary_function or binary_function as an argument, instead of any old function object. We can create one using std::ptr_fun(), although for some reason we need to explicitly tell it what the template parameters are. And we need to use std::isalpha() instead of isalpha() in order to get the locale-enabled version. So the full expression looks like

std::bind2nd(std::ptr_fun<char, const std::locale&, bool>(std::isalpha), loc)

Needless to say, the C++11 version is vastly simpler.

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BTW if you are using C++11 then you can use std::any_of(...) instead of std::find_if(...) == foo.end(). It should behave the same, but be slightly more readable.