Q: C++ string library, to get a string by removing the integers in it I've a string like "Hello world 1 2 3" and I want to get a string like "Hello World". Do you know any function for it?

A: As a first approximation, assuming you want all digits removed and the result put into a new string, I'd start with something like this:
std::remove_copy_if(your_string.begin(), your_string.end(), 
                    std::back_inserter(new_string),
                    [](unsigned char ch) { return isdigit(ch); });


A: Remove all digits from string
string x
x.erase(
  std::remove_if(x.begin(), x.end(), &isdigit), 
  x.end());


A: This is typically done using the std::ctype<char> facet to classify alphanumeric including whitespace characters:
#include <locale>
#include <functional>

template <class charT = char>
bool digit_removal(charT c, std::locale loc)
{
    return std::use_facet<std::ctype<charT>>(loc).is(
        std::ctype_base::digit, c);
}

int main()
{
    std::string var = "Hello 123";
    var.erase(
        std::remove_if(var.begin(), var.end(),
          std::bind(&digit_removal<char>, std::placeholders::_1, std::locale())),
    var.end());


    std::cout << var; // "Hello "
}

