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 working on and apparently this kind of optimization matters to him.

I've came up with the following code, it uses strtok().

bool has_only_spaces(std::string& str) {     char* token = strtok(const_cast<char*>(str.c_str()), " ");      while (token != NULL)     {            if (*token != ' ')         {                return true;         }        }        return false; } 

I'm looking for feedback on this code and more efficient ways to perform this task are also welcome.

Answer 1

if(str.find_first_not_of(' ') != std::string::npos) {     // There's a non-space. } 

Answer 2

In C++11, the all_of algorithm can be employed:

// Check if s consists only of whitespaces bool whiteSpacesOnly = std::all_of(s.begin(),s.end(),isspace);