visual c++ - C++ question regarding inserting elements into vectors -

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i working through examples in accelerated c++. 1 of problems asks reader copy records students pass exams beginning of vector called students. fgrade function defined elsewhere returns failing students. 1 has use resize function remove elements students contains pass. have tried code not work. tell me if fault lies in code below?

#include "stdafx.h"  #include <vector> #include "student_info.h" #include "grade.h"  using std::vector;  // second try: correct potentially slow vector<student_info> extract_fails(vector<student_info>& students) {     vector<student_info> fail; #ifdef _msc_ver     std::vector<student_info>::size_type = 0;     std::vector<student_info>::size_type count = 0; #else     vector<student_info>::size_type = 0;     vector<student_info>::size_type count = 0; #endif      while (i != students.size()) {          if (!fgrade(students[i])) {              students.insert(students.begin(), students[i++]);             count++;         }         i++;      }     students.resize(count);      return students; }

you increment i twice in loop.

a cool way use custom predicate std::sort:

bool comparestudentsbyfailure(const student_info & left,                                const student_info & right) {    return fgrade(left) > fgrade(right); }

and use this:

std::sort(students.begin(), students.end(), comparestudentsbyfailure); students.resize(std::distance(students.begin(),                  std::find_if(students.rbegin(),                               students.rend(), fpgrade).base()));

however, jon`s answer bit simpler.


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