C++ 如何使用 .find_first_not_of()

Question

I am supposed to be checking to make sure my number is in the base. ex: if the base was 10 only the first 10 characters from base value could be used (0-9). When i try to run my code i keep getting this message "[Error] invalid conversion from 'std::basic_string::size_type {aka long long unsigned int}' to 'const char*' [-fpermissive]" can someone please help me?

const string base_vals = "0123456789abcdefghijklmnopqrstuvwxyz";
string metadrome(string n, int base){
    string new_base_vals= base_vals.substr(0,base);
    string number=n;
    string q = number.find_first_not_of(new_base_vals)
    return q;
}

edit: this is not the full code just a small portion in which I'm having difficulty the input string n and int base are user entered values

Answer 1

The return value of std::string::find_first_not_of() is a size_t . You need to change the call to

size_t q = number.find_first_not_of(new_base_vals);

Don't forget to change the signature of metadrome() as well.