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

Using strtok like that is bad style! strtok modifies the buffer it tokenizes (it replaces the delimiter chars with \0).

Here's a non modifying version.

const char* p = str.c_str();
while(*p == ' ') ++p;
return *p != 0;

It can be optimized even further, if you iterate through it in machine word chunks. To be portable, you would also have to take alignment into consideration.