Calling function from different files in C++ error

Question

I would like to use one function from Stats.cpp in Application.cpp. Here are my code snippets:

In Stats.h:

#ifndef STATS_H
#define STATS_H

class Stats
{
public:
    void generateStat(int i);
};

#endif

In Stats.cpp:

#include Stats.h
void generateStat(int i)
{
    //some process code here
}

In Application.cpp:

int main()
{
    generateStat(10);
}

I get an "unresolved external symbol" error however I don't know what I else I would need to include in order for Application.cpp. Any thoughts?

This is funny... The call generateStat(10) seems to be accepted by the compiler without any previous declaration. Is that C++? — user2033018
– user2033018, Commented Mar 26, 2014 at 20:16

P0W · Accepted Answer · 2014-03-26 20:14:22Z

2

In Stats.cpp

you need to define generateStat like following :

#include Stats.h
void Stats:: generateStat(int i) // Notice the syntax, use of :: operator
{
    //some process code here
}

Then create object of class Stats, use it to call the public member function generateStat

Stats s;
s.generateStat( 10 ) ;

Build the application using :

g++ -o stats Stats.cpp Application.cpp -I.

answered Mar 26, 2014 at 20:14

P0W

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Comments

user2591612 · Accepted Answer · 2014-03-26 20:12:57Z

0

generateStat is part of your Stats class. You need to instantiate a Stats object (along with the necessary includes for Stats.h in your main class)

For example,

Stats stat;
stat.generateStat(i);

Also, your function definition needs to include the class name Stats::generateStat.

answered Mar 26, 2014 at 20:12

user2591612

Comments

mnemonic · Accepted Answer · 2014-03-26 20:53:21Z

0

The same error msg occured 2 weeks ago (at work).

At first glance --- Try:

 void Stats::generateStat(int i) {
     //some process code here }

The class name was missing. Hence, unresolved.

btw Concerning your header --- another issue, this #ifndef directive should not be necessary cause you should declare Stats only once in a namespace.

#ifndef CLASS_H
#define CLASS_H
#include "Class.h"
#endif

This is a generic example - Usable in cpp files.

EDIT: Now, I saw your invocation (main method in your case). You need an object instance to invoke your method.

Stats* stats = new Stats(); //add a default constructor if not done
stats->generateStat(77);

// any other stats stuff ......
// in posterior to the last use
delete(stats);

In your header:

Stats::Stats(){}; //with an empty body - no need to write it again in the cpp file

edited Mar 26, 2014 at 20:53

answered Mar 26, 2014 at 20:19

mnemonic

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4 Comments

codah Over a year ago

You have a few issues with this code, better check it over.

mnemonic Over a year ago

@codah what are u talking about?

codah Over a year ago

Firstly Stats stats should be Stats* stats. And then you would have to change stats.generateStat to stats->generateStat. Why not just create it on the stack anyway? And you didn't delete it (might as well show that if you're going to advocate creating on the heap).

mnemonic Over a year ago

@codah +1 && yes, did not focus on that

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