Question

Basically I have string of whitespace " " or blocks of whitespace or "" empty in some of the lines of the files and I would like to know if there is a function in C++ that checks this.

*note:* As a side question, in C++ if I want to break a string down and check it for a pattern which library should I use? If I want to code it myself which basic functions should I know to manipulate string? Are there any good references?

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 <string>
#include <cctype>

// 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;
}