C++ check if string is space or null

Question

Basically I have string of whitespace \" \" or blocks of whitespace or \"\" empty in some of the lines of the files and I would

Answer 1

Since you haven't specified an interpretation of characters > 0x7f, I'm assuming ASCII (i.e. no high characters in the string).

#include 
#include 

// Returns false if the string contains any non-whitespace characters
// Returns false if the string contains any non-ASCII characters
bool is_only_ascii_whitespace( const std::string& str )
{
    auto it = str.begin();
    do {
        if (it == str.end()) return true;
    } while (*it >= 0 && *it <= 0x7f && std::isspace(*(it++)));
             // one of these conditions will be optimized away by the compiler,
             // which one depends on whether char is signed or not
    return false;
}