undefined reference to (errors) something about my compiler linking

[goldn]

I'm new to c++ programming and started to work my way through the book Accelerated C++. When I tried to compile the program from Ch4 which had header files and source files I got these errors:

obj/Debug/main.o||In function `main':|
/home/x/Desktop/programming/4.0/main.cpp|26|undefined reference to `read(std::basic_istream<char, std::char_traits<char> >&, Student_info&)'|
/home/x/Desktop/programming/4.0/main.cpp|33|undefined reference to `compare(Student_info const&, Student_info const&)'|
/home/x/Desktop/programming/4.0/main.cpp|45|undefined reference to `grade(Student_info const&)'|
||=== Build finished: 3 errors, 0 warnings ===|

I tried to find a solution on my own but after hours of searching the only thing I learned is that its something about linking and my GNU GCC compiler. I'm using the IDE Code::Blocks.

Here is the main function and the header and source that are giving me the problems

int main()
{
    vector<Student_info> students;
    Student_info record;
    string::size_type maxlen = 0;       // the length of the longest name

    // read and store all the students data.
    // Invariant:  students contains all the student records read so far
    //   maxlen contains the length of the longest name in students
    while (read(cin, record)) {
        // find length of longest name
        maxlen = max(maxlen, record.name.size());
        students.push_back(record);
    }

    // alphabetize the student records
    sort(students.begin(), students.end(), compare);

    // write the names and grades
    for (vector<Student_info>::size_type i = 0;
         i != students.size(); ++i) {

        // write the name, padded on the right to maxlen + 1 characters
        cout << students[i].name
             << string(maxlen + 1 - students[i].name.size(), ' ');

        // compute and write the grade
        try {
            double final_grade = grade(students[i]);
            streamsize prec = cout.precision();
            cout << setprecision(3) << final_grade
                 << setprecision(prec);
        } catch (domain_error e) {
            cout << e.what();
        }
        cout << endl;
    }
    return 0;
}

My header file Student_info.h

#ifndef STUDENT_INFO_H_INCLUDED
#define STUDENT_INFO_H_INCLUDED

// Student_info.h header file
#include <iostream>
#include <string>
#include <vector>

struct Student_info {
	std::string name;
	double midterm, final;
	std::vector<double> homework;
};

bool compare(const Student_info&, const Student_info&);
std::istream& read(std::istream&, Student_info&);
std::istream& read_hw(std::istream&, std::vector<double>&);


#endif // STUDENT_INFO_H_INCLUDED 

My source file Student_info.cpp

#include "Student_info.h"

using std::istream;  using std::vector;

bool compare(const Student_info& x, const Student_info& y)
{
    return x.name < y.name;
}

istream& read(istream& is, Student_info& s)
{
    // read and store the student's name and midterm and final exam grades
    is >> s.name >> s.midterm >> s.final;

    read_hw(is, s.homework);  // read and store all the student's homework grades
    return is;
}

// read homework grades from an input stream into a `vector'
istream& read_hw(istream& in, vector<double>& hw)
{
    if (in) {
        // get rid of previous contents
        hw.clear();

        // read homework grades
        double x;
        while (in >> x)
            hw.push_back(x);

        // clear the stream so that input will work for the next student
        in.clear();
    }
    return in;

As far as I can tell, there is nothing wrong with my code, I double checked it with the book's code a few times. It's something to do with my compiler's method of linking and I don't know how to link or what option I need to change so that it does link.

Compiler : GNU GCC Compiler
IDE : Code::Blocks

[Athar]

You probably forgot to add Student_info.cpp to your project.
If you don't do that, it won't be linked (or even compiled).

[goldn]

It's in my project folder and it opens when I open the project, thanks though.

[Athar]

That's not sufficient. In the project management window to the left it needs to appear under "Sources".

[goldn]

All of my headers and sources are under the header and source trees in the project management window.