20121031.cpp

#include <string>
#include <fstream>
#include <iostream>
#include <sstream>
#include <vector>
#include <stdexcept>

class studentfile {
    public:
        studentfile(const std::string &filename);
        void print_out(std::ostream &where);
    private:
        struct student {
            std::string name;
            double gpa;
            long id;
            char gender;
            student() : name(""), gpa(0), id(0), gender('?') {};
            student(std::istringstream &n) : name(n.str()), gpa(0), id(0), gender('?') {};
        };
        std::vector<student> students;
};

static bool case_insensitive_equals(const std::string &lhs, const std::string &rhs)
{
    if(lhs.size() != rhs.size())
        return false;
    for(size_t i = 0; i < lhs.size(); i++)
        if(std::tolower(lhs[i]) != std::tolower(rhs[i]))
            return false;
    return true;
}

studentfile::studentfile(const std::string &filename)
{
    std::ifstream in(filename.c_str());
    
    if(!in)
        throw std::runtime_error("Can't open file");
    
    student cur_student;
    std::string line;
    while(getline(in, line)) {
        size_t lhs_begin = line.find_first_not_of(" \t");
        if(lhs_begin == std::string::npos || line[lhs_begin] == '#')
            continue;

        size_t lhs_end = line.find_first_of("= \t", lhs_begin);
        if(lhs_end == std::string::npos)
            continue;

        size_t rhs_begin = line.find_first_not_of("= \t", lhs_end);
        if(rhs_begin == std::string::npos)
            continue;
               
        std::string lhs(line.substr(lhs_begin, lhs_end - lhs_begin));
        std::istringstream rhs(line.substr(rhs_begin, std::string::npos));
        
        if(case_insensitive_equals(lhs, "name")) {
            if(cur_student.name.size())
                students.push_back(cur_student);
            cur_student = student(rhs);
        } else if(case_insensitive_equals(lhs, "gpa"))
            rhs >> cur_student.gpa;
        else if(case_insensitive_equals(lhs, "id"))
            rhs >> cur_student.id;
        else if(case_insensitive_equals(lhs, "gender"))
            rhs.get(cur_student.gender);
    }
    if(cur_student.name.size())
        students.push_back(cur_student);
}

void studentfile::print_out(std::ostream &where)
{
    for(std::vector<student>::iterator i = students.begin(); i != students.end(); i++)
        where << "name: " << i->name << ", id: " << i->id << ", gender: " << i->gender << ", gpa: " << i->gpa << std::endl;
}

int main()
{
    studentfile sf("20121031.txt");
    sf.print_out(std::cout);
}

20121031.txt

name = Rick James
ID= 123456
GPA =9.2
gender=M

# mixed items
name = Hermione Granger
GPA = 11.2
gender = f
ID = 123457

# mixed, missing, and extra fields
name = Henry Ramirez
GPA = 12.3
ID = 111888
major = ChE
class = soph
ID = 788531

# missing fields
name=Suzie Shah
geNDEr=t

gistfile1.txt

$ g++ -Wall -Wextra -pedantic -O2 -g -std=c++98 20121031.cpp -o 20121031

$ ./20121031
name: Rick James, id: 123456, gender: M, gpa: 9.2
name: Hermione Granger, id: 123457, gender: f, gpa: 11.2
name: Henry Ramirez, id: 788531, gender: ?, gpa: 12.3
name: Suzie Shah, id: 0, gender: t, gpa: 0