undefined reference errors in C++

Question

I have files Record.h and Record.cpp. When I just include the Record.h file, I get several undefined reference errors to functions defined in those files. When I also include Record.cpp then the errors go away. Why is that? Record.h has the forward declarations for the functions it says are an undefined reference.

Record.h

#ifndef RECORD_
#define RECORD_

#include <string>
#include <limits>
using namespace std;

#define PKEYSIZE 10
#define STREETNUMSIZE 8
#define STREETNAMESIZE 24
#define RNAMESIZE 30
#define ASTYLESIZE 20
#define YEARSIZE 12

#define MAXBUCKETSIZE 4
#define MAXDIRECTORYSIZE 100

typedef struct
{

        char streetNum[STREETNUMSIZE];
        char streetName[STREETNAMESIZE];
        char rName[RNAMESIZE];
        char aStyle[ASTYLESIZE];
        char year[YEARSIZE];
        char pkey[PKEYSIZE];

} RECORD;

typedef struct
{
    int size;
    int depth;
    RECORD record[MAXBUCKETSIZE];

} BUCKET;


#define HEADERSIZE 2L

#define NODESIZE sizeof(BUCKET)

void addKey(RECORD *rec_ptr, string key);
void addStreetNum(RECORD *rec_ptr, string s);
void addStreetName(RECORD *rec_ptr, string s);
void addRName(RECORD *rec_ptr, string s);
void addAStyle(RECORD *rec_ptr, string s);
void addYear(RECORD *rec_ptr, string s);
void printRecord(RECORD *rec_ptr);
ostream & operator<<(ostream & out, RECORD *r);

string cvt_binary(unsigned int input);
void addRecord(RECORD *r);
void showbucket(int n);

#endif

Record.cpp

int dirDepth = 0;
int numberOfBuckets = 0;
int directory[MAXDIRECTORYSIZE];
BUCKET bucket[MAXDIRECTORYSIZE/MAXBUCKETSIZE];

void addKey(RECORD *rec_ptr, string key)
{
    strncpy(rec_ptr->pkey, key.c_str(), PKEYSIZE);

}

void addStreetNum(RECORD *rec_ptr, string s)
{
    strncpy(rec_ptr->streetNum, s.c_str(), STREETNUMSIZE);
}

void addStreetName(RECORD *rec_ptr, string s)
{
    strncpy(rec_ptr->streetName, s.c_str(), STREETNAMESIZE);
}

void addRName(RECORD *rec_ptr, string s)
{
    strncpy(rec_ptr->rName, s.c_str(), RNAMESIZE);
}

void addAStyle(RECORD *rec_ptr, string s)
{
    strncpy(rec_ptr->aStyle, s.c_str(), ASTYLESIZE);
}


void addYear(RECORD *rec_ptr, string s)
{
    strncpy(rec_ptr->year, s.c_str(), YEARSIZE);
}

void printRecord(RECORD *rec_ptr)
{

    cout<< "|"
        << rec_ptr->pkey << "|" 
        << rec_ptr->streetNum << "|" 
        << rec_ptr->streetName << "|" 
        << rec_ptr->rName << "|" 
        << rec_ptr->aStyle << "|" 
        << rec_ptr->year << endl;

}


ostream & operator<<(ostream & out, RECORD *r)
{
    out << r->pkey << r->streetNum << r->streetName << r->rName
        << r->aStyle << r->year << endl;
    return out;

}

int bucketread(short rrn, BUCKET *page_ptr)
{
//  long lseek(), addr;
    long addr;

    addr = (long)rrn * (long)NODESIZE + HEADERSIZE;
    lseek(btfd, addr, 0);
    return ( read(btfd, page_ptr, NODESIZE) );
}

int bucketwrite(short rrn, BUCKET *page_ptr)
{
//    long lseek(), addr;
    long addr;
    addr = (long) rrn * (long) NODESIZE + HEADERSIZE;
    lseek(btfd, addr, 0);
    return (write(btfd, page_ptr, NODESIZE));
}

void showbucket(int n)
{
    cout << "loading bucket " << n << endl;
    BUCKET b;
    bucketread(n, &b);
    cout << "there are " << b.size << " records in the bucket" << endl;

}

string cvt_binary(unsigned int input) {
    if(input == 0) return "0"; // trivial case
    string result;
    for(int i = numeric_limits<unsigned int>::digits - 1; i >= 0; --i) {
        if(input & (1 << i)) 
        {
            result += "1";
        } 
        else 
        {
            if(!result.empty()) result += "0";
        }
    }
    return result;
}


string hash (char* key)
{
    int sum = 0;
    int len = strlen(key);
    if (len % 2 == 1) len++; // make len even
    //for an odd length string, use the trailing 0 as part of key
    for (int j = 0; j < len; j +=2)
        sum = (sum + 100 * key[j] + key[j+1]) % 19937;
    return cvt_binary(sum);
}

void copyrecord(RECORD *dest, RECORD *src)
{
    cout << "copying record" << endl;
    addKey(dest, src->pkey);
    addStreetNum(dest, src->streetNum);
    addStreetName(dest, src->streetName);
    addRName(dest, src->rName);
    addAStyle(dest, src->aStyle);
    addYear(dest, src->year);
}

void addToBucket(int n, RECORD *r)
{
    cout << "Adding record " << r->pkey << " to bucket " << n << endl;
    if (bucket[n].size == MAXBUCKETSIZE)
    {
        cout << "Bucket " << n << " is full." << endl;
        // examine bucket depth and directory depth to determine next action
        cout << "Bucket depth: " << bucket[n].depth << endl;
        cout << "Directory depth: " << directory[0] << endl;
    }
    else
    {
        copyrecord(&bucket[n].record[bucket[n].size],r);
        bucket[n].size++;
        bucketwrite(1,&bucket[1]);


    }

}

string getreverse(string key, int num)
{
    if(num==0)
        return "";
    string newstring;
    newstring = key.at(key.length());
    newstring+= getreverse(key.substr(0,key.length()-1),num-1);

    return newstring;
}

void addRecord(RECORD *r)
{
    cout << r->pkey << endl;
    string hashvalue = hash(r->pkey);
    cout << "hash value is " << hashvalue << endl;

    int directoryDepth = directory[0];

    if(directoryDepth == 0)
    {
        directory[1] = 1;
        addToBucket(1, r);
    }
    else
    {
        // use hashing to figure out which bucket to add to
        cout << "The relevant string is" <<  getreverse(hashvalue, directoryDepth) << endl;

    }

}

Answer 1

Providing the declarations by including the header is what the compiler needs. The linker needs the definitions. It will find these in the object files the compiler creates when it compiles source files.
I'm not using gcc, but I think it can just be called with all the source files and will then call the linker with all the object files provided: g++ main.cpp record.cpp.

Answer 2

Record.h has the declarations of those functions. Record.cpp has the definitions.

//Record.h

void foo(); // This is a forward declaration

So far so good.

//main.cpp

#include "Record.h"

int main()
{
    foo();
}

Now main.o will compile just fine. But if you try to link it into a working binary, you'll get a complaint that void foo() is undefined.

//Record.cpp

#include "Record.h"

// This is the definition
void foo()
{
    // do various things
}

This can be compiled into Record.o, which can then be linked with main.o into a working executable.

Answer 3

My C++ might be a bit rusty, but it sounds like Record.cpp isn't being compiled into the solution. If the .cpp file isn't there, then the header has nothing to refer to. Don't include the cpp, but check your linker settings, or the command you're using to compile your program... it needs to include all the cpps.