CODEWITHSUNDEEP
c++filecompilationheader
Sergey
Sergey

Reputation: 11908

Using static class in c++

I have some simple hypothetical static class in C++:

#ifndef __STAT_H_
#define __STAT_H_

class Stat {

 private:
  static vector<int> v;

 public:

  static void add_num(int num);
  static void clear_nums();
  static void get_count();
};

#endif

And the ccp file is so:

#include "Stat.h"

vector<int> v;


void Stat::add_num(int num) {
  v.push_back(num);
}

void Stat::clear_nums() {
  v.clear();
}

int Stat::get_num_count() {
  return v.size();
}

Now when I include in main.cpp file "Stat.h" and try to use some static method:

Stat::add_num(8);

the error during compilation is

undefined reference to 'Stat::add_num(int)'

What can be the problem in this case? Thank you.

EDIT: sorry about addresses vector, it should be v there

Upvotes: 0

Views: 797

Answers (3)

Dennis
Dennis

Reputation: 59489

Here's my take on your program, just for reference sake.

Stat.h

#ifndef STAT_H
#define STAT_H

#include <vector>
using std::vector;

class Stat
{
 public:
  static void add_num(int num);
  static void clear_nums();
  static int get_count();

 private:
  static vector<int> v;
};

#endif

Stat.cpp

#include "Stat.h"

vector<int> Stat::v;

void Stat::add_num(int num) { v.push_back(num); }

void Stat::clear_nums() { v.clear(); }

int Stat::get_count() { return v.size(); }

main.cpp

#include "Stat.h"

int main()
{
  Stat s;
  s.add_num(8);
}

Makefile

CC = g++
OBJS = Stat.o
DEBUG = -g
CFLAGS = -Wall -c $(DEBUG)
LFLAGS = -Wall $(DEBUG)

all: build clean

build: $(OBJS)
        $(CC) main.cpp $(LFLAGS) $(OBJS) -o stat

Stat.o: Stat.h
        $(CC) $(CFLAGS) Stat.cpp

clean:
        -rm -f *.o

Upvotes: 1

billz
billz

Reputation: 45410

You need to link Stat.o in g++ command, say:

g++ -c -o Stat.o Stat.cpp
g++ -o Stat main.cpp Stat.o

I guess in your Stat.cpp:

vector<int> v;

should be:

vector<int> Stat::v;

There is no compile error if you define local v in Stat.cpp but I guess you intent to use Stat::v

Upvotes: 1

unknownuser
unknownuser

Reputation: 800

It sounds like you have not included stat.cpp in compilation. So your linker cannot find an implementation for the static methods.

Upvotes: 3

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