how can I call a method from another class? - c++

Question

I have 3 files pos.h pos.cpp and main.cpp .... I am trying to call a function from pos.cpp in the main class for instance :
pos.h file
class pos {
public:
pos(); //defualut constructor
int open_port();
}
pos.cpp
#include "pos.h"
int Open_port() {
//do stuff here
return 0;
}
class main.cpp
#include "pos.h"
int main(int argc , char** argv) {
pos pos1;
pos1::Open_port();
}
Problem is I always get that pos1 is not a class or namespace I am compining as follows
g++ mainpos.cpp pos.cpp pos.h -o position -lpthread
Any thoughts ?

Answer 1

You seems to have several issues in the code:
int open_port();
is a member function of pos. However, when you define it, you are not using :: operator and the function name is changed.
Try:
int pos::open_port()
{ ///^^pay attention to typos
//do stuff here
return 0;
}
Then inside main. you can do:
pos pos1;
pos1.open_port();
If you really mean Open_port(), which is not a member of the class, then you need to add function declaration into the proper header files and use it properly, but that's a separate issue.

Answer 2

You've several problems, most of them related to fundamental syntax:
Case matters. open_port and Open_port are two completely different things
You're not actually defining the method of the class pos, you're making a new function
int Open_port() {
needs to be
int pos::open_port() {
You're trying to invoke a non-static method statically. You need to create an instance of pos, (which you've done, pos1) and invoke open_port on it via pos1.open_port(). You cannot call pos::open_port directly, unless you declare the method static.
A final problem would be that you've declared but not defined the default constructor for your class. You need to provide a method body for pos::pos().

Answer 3

Well, you have two problems with your code. In the cpp file you need to use the scope for that function, so you need to have:
int pos::Open_port()
Also, you need to ensure that open_port and Open_port are spelled and capitalized the same.
Last thing, if you want to call open_port like that, you'll need to decare the function as static in the class def'n.