c++ - libc++abi.dylib: terminate called throwing an exception -

exercise 4-6 of accelerated c++ wants me write program reads in , calculates student's overall grade. have following code:

// source file student_info-related functions #include "student_info.h" #include "grade.h"  using std::istream;  using std::vector; using namespace std;  bool compare(const student_info& x, const student_info& y) {     return x.name < y.name; }  istream& read(istream& is, student_info& s) //void read(istream& is, student_info& s) {      double midterm, final;      // read , store student's name , midterm , final exam grades     >> s.name >> midterm >> final;      std::vector<double> homework;     read_hw(is, homework);  // read , store student's homework grades      s.grade = grade(midterm, final, homework);      cout << "name is: " << s.name << endl; ///    cout << "midterm is: " << midterm << endl; ///    cout << "final is: " << final << endl;     cout << "grade is: " << s.grade << endl;     cout << "" << endl;      return is; }  // read homework grades input stream 'vector<double>' istream& read_hw(istream& in, vector<double>& hw) {     cout << "i read_hw!" << endl;      if (in) {         // rid of previous contents         hw.clear();          // read homework grades         double x;         while (in >> x)             hw.push_back(x);          // clear stream input work next student         in.clear();     }     cout << "i (just before) out of read_hw!" << endl;     return in; } 

with above being called main() such:

int main() {     vector<student_info> students;     student_info record;     string::size_type maxlen = 0;       // length of longest name      // read , store students data.     // invariant: students contains student records read far     //          maxlen contains length of longest name in students     while (read(cin, record)) {         cout << "get read() while loop" << endl;         // find length of longest name         maxlen = max(maxlen, record.name.size());         students.push_back(record);         cout << "get end of read() while loop" << endl;     }     cout << "i out of read ok!!" << endl;  // never far 

here output:

(canopy 32bit) joes-imac:4-6 david$ make test  ./main <data/gradestest read_hw! (just before) out of read_hw! name is: moo grade is: 100  read() while loop end of read() while loop read_hw! (just before) out of read_hw! name is: moore grade is: 79.4  read() while loop end of read() while loop read_hw! (just before) out of read_hw! name is: norman grade is: 72.8  read() while loop end of read() while loop read_hw! (just before) out of read_hw! libc++abi.dylib: terminate called throwing exception /bin/sh: line 1: 20610 abort trap: 6           ./main < data/gradestest make: *** [test] error 134 (canopy 32bit) joes-imac:4-6 david$  

why fail? why seem blank run (i.e. not read in data) program fails (the data input not have blank line @ end or that)?

what input last loop? trying end loop sending non-numeric values midterm , final values? looks error happening when calculating grade using numbers. guess try doing this:

if (is) {     s.grade = grade(midterm, final, homework); }