Efficient way to check if std::string has only spaces

Question

I was just talking with a friend about what would be the most efficient way to check if a std::string has only spaces. He needs to do this on an embedded project he is worki

Answer 1

it's highly unlikely you'll beat a compiler optimized naive algorithm for this, e.g.

string::iterator it(str.begin()), end(str.end())    
for(; it != end && *it == ' '; ++it);
return it == end;

EDIT: Actually - there is a quicker way (depending on size of string and memory available)..

std::string ns(str.size(), ' '); 
return ns == str;

EDIT: actually above is not quick.. it's daft... stick with the naive implementation, the optimizer will be all over that...

EDIT AGAIN: dammit, I guess it's better to look at the functions in std::string

return str.find_first_not_of(' ') == string::npos;