All that really does not need to just check whether there is a gap in it. This is all you need:
#include <ctype.h> bool hasspace = std::find_if(str.begin(), str.end(), ::isspace) != str.end();
:: is a scope resolution statement indicating that isspace is a global function, not the so-called std::isspace and find_if is a function inside std:: . If you are using namespace std; , you do not need std:: , but you still need a simple :: .
The find_if function takes an iterator at the beginning of a line, an iterator at the end of a line, and a function that takes an argument and returns some value convertible to bool . find_if from the first iterator to the second iterator, passing each value of the current element of the function that you gave it, and if the function returns true , find_if returns an iterator that caused the function to return true . If find_if passes to the end, and the function never returns true , it returns an iterator to the end of the range, which in this case is equal to str.end() .
This means that if find_if returns str.end() , it isspace to the end without isspace returning true , which means there were no spaces in the line. Therefore, you can check the result of find_if on str.end() ; If they are not equal ( != ), This means that there is a space in the line, and hasspace is true . Else, hasspace - false .