Question

我有Record.h和Record.cpp文件。当我只包含Record.h文件时，我会在这些文件中定义的函数中获得几个未定义的引用错误。当我还包括Record.cpp时，错误就会消失。这是为什么？ Record.h具有函数的前向声明，它声称是未定义的引用。

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

Record.h具有这些功能的声明。 Record.cpp具有定义。

//Record.h

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

到目前为止一切顺利。

//main.cpp

#include "Record.h"

int main()
{
    foo();
}

现在main.o会编译得很好。但是，如果您尝试将其链接到工作二进制文件，则会收到void foo()未定义的投诉。

//Record.cpp

#include "Record.h"

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

这可以编译成Record.o，然后可以将其与main.o链接到工作的可执行文件中。

Answer 2

通过包含标题提供声明是编译器所需要的。 链接器需要定义。它会在编译器编译源文件时在编译器创建的目标文件中找到它们我没有使用gcc，但我认为可以使用所有源文件调用它，然后使用提供的所有目标文件调用链接器：g++ main.cpp record.cpp。

Answer 3

我的C ++可能有点生疏，但听起来Record.cpp没有被编译到解决方案中。如果.cpp文件不存在，则标题中没有引用。不要包含cpp，但要检查链接器设置，或者用于编译程序的命令......它需要包含所有cpps。

C ++中未定义的引用错误

3 个答案: