Problems with functions in classes C++ (LNK2019 & LNK1120 errors) - c++

Question

I've been working on a project for my college class that uses classes in c++, unfortunately anytime I try to call on a function that is passed parameters within my class the program fails to compile with the two following errors:
Error LNK2019 unresolved external symbol "int __cdecl binsearch(class Course * * const,int,char * const)" (?binsearch##YAHQAPAVCourse##HQAD#Z) referenced in function _main Project1 C:\Users\cvos\source\repos\Project1\Project1\courses_main.obj 1
and
Error LNK1120 1 unresolved externals Project1 C:\Users\cvos\source\repos\Project1\Debug\Project1.exe 1
I've looked up the LNK problems, and most results suggest it's something related to symbols in c++ vs c (That fix doesn't work) or that there is a problem with linking the files within visual studio (That fix also didn't work), and finally that it was something to do with it needing to be on the console subsystem (Which it already was).
The strange thing is, if I comment out my calls to all of the functions I've made in the "Course" class that are passed parameters, the program runs fine. It's only when I am trying to use the functions created in the "Course" class that the program fails to run, leading me to suspect strongly I'm doing something wrong with how I'm passing variables to my member functions.
I'll post the relevant parts of my code:
Within my header file "courses.h" I declare my function:
int binsearch(Course* co_ptr[], int size, char search[]);
Within my 2nd source file "courses_functions.cpp" I define the function:
int Course::binsearch(Course* co_ptr[], int size, char search[])
{
int low = 0, high = size - 1, first_index = -1, last_index = -1, num_of_entries = 0;
while (low <= high)
{
int mid = (low + high) / 2;
if (co_ptr[mid]->name == search)
{
bool found = false;
int i = mid;
while (!found) //Check values below mid
{
if (co_ptr[i]->name == search)
{
first_index = i; //first_index now holds a potential first occurence of our name
if (i == 0)
{
found = true;
}
}
else
{
found = true;
}
i--; //decrement i and check again.
}
i = mid; //Reset i
found = false; //Reset found
while (!found) //Check values above mid
{
if (co_ptr[i]->name == search)
{
last_index = i; //last_index now holds a potential last occurence of our name
if (i == size - 1)
{
found = true;
}
}
else
{
found = true;
}
i++; //increment i and check again.
}
break; //Breaks us out of the main while loop
}
else if (co_ptr[mid]->name < search)
{
low = mid + 1;
}
else
{
high = mid - 1;
}
}
if ((first_index != -1) && (last_index != -1))
{
for (int i = first_index; i <= last_index; i++)
{
std::cout << "\nEntry found: "
<< std::endl << co_ptr[i]->name << ' ' << co_ptr[i]->units << " units, grade:" << co_ptr[i]->grade;
num_of_entries++;
}
return num_of_entries;
}
else
{
std::cout << "\nEntry not found.";
return num_of_entries;
}
}
Lastly in my main source file "courses_main.cpp" I call the function:
else if (selection == 3) //Display a course
{
char title[50] = "";
int results = 0;
std::cout << "\nEnter a class to search for: ";
std::cin.getline(title, 50, '\n');
std::cin.ignore();
results = binsearch(courses, size, title);
}
As this is for a college class, I'm not looking to use any alternative methods, I'm mainly trying to figure out why the method I'm using would return the errors I shared above, but I will gladly post more snippets of my code if it is necessary.
Thanks!

Answer 1

The cause is almost certainly one of the following:
You're not compiling the implementation file (just using the header elsewhere).
You're compiling the implementation, but not using the compiled object in the linking of objects into the executable.
You have some minor mismatch in naming, e.g. using binsearch() not in a class context, or using a slightly different signature somehow (not likely giving what you've told us).

Answer 2

Need to see a declaration of your "courses.h" file. You may have declared binsearch outside of your Course class declaration. In which case you will get a linker error as mentioned.
Based on your usage in main.. your implementation of this function need not be in Course class, it can be a standalone function outside of Course class. once you move your function definition outside of Course class, your linker should go away, provided you have courses_functions.cpp and courses_main.cpp files in same project in your MSVC IDE.