How to negate a predicate function using operator ! in C++?
- by Chan
Hi,
I want to erase all the elements that do not satisfy a criterion. For example: delete all the characters in a string that are not digit. My solution using boost::is_digit worked well.
struct my_is_digit {
bool operator()( char c ) const {
return c >= '0' && c <= '9';
}
};
int main() {
string s( "1a2b3c4d" );
s.erase( remove_if( s.begin(), s.end(), !boost::is_digit() ), s.end() );
s.erase( remove_if( s.begin(), s.end(), !my_is_digit() ), s.end() );
cout << s << endl;
return 0;
}
Then I tried my own version, the compiler complained :(
error C2675: unary '!' : 'my_is_digit' does not define this operator or a conversion to a type acceptable to the predefined operator
I could use not1() adapter, however I still think the operator ! is more meaningful in my current context. How could I implement such a ! like boost::is_digit() ? Any idea?
Thanks,
Chan Nguyen
