Question

所以，我以为我正在完成我的计划。我编译了它并得到了一堆LNK（2019和2001）错误。

我确实对它们进行了一些研究，一个流行的解决方案是摆脱导致错误的代码。这似乎不完全正确。我试了一下，但没办法。

这是错误分支的文件。

我正在研究如何解决这些错误..我以前从未遇到过LNK错误。

错误：

1＆gt; bankingdriver.obj：错误LNK2019：未解析的外部符号“public：__thiscall Account :: ~Account（void）”（?? 1Account @@ QAE @ XZ）在函数“void __cdecl createTextFile（class std ::）中引用basic_fstream＆gt;＆amp;）“（？createTextFile @@ YAXAAV？$ basic_fstream @ DU？$ char_traits @ D @ std @@@ std @@@ Z）

1＆gt; bankingdriver.obj：错误LNK2019：未解析的外部符号“void __cdecl outputLine（class std :: basic_ostream＆gt;＆amp; class class const＆amp;）”（？outputLine @@ YAXAAV？$ basic_ostream @ DU？$ char_traits @ D @ std @@@ std @@ ABVAccount @@@ Z）在函数“void __cdecl createTextFile（class std :: basic_fstream＆gt;＆amp;）”中引用（？createTextFile @@ YAXAAV？$ basic_fstream @ DU？$ char_traits @ d @ STD @@@ STD @@@ Z）

1＆gt; bankingdriver.obj：错误LNK2019：未解析的外部符号“public：double __thiscall Account :: getBalance（void）”（？getBalance @ Account @@ QAENXZ）在函数“void __cdecl updateRecord（class std :: basic_fstream”）中引用＆gt;＆amp;）“（？updateRecord @@ YAXAAV？$ basic_fstream @ DU？$ char_traits @ D @ std @@@ std @@@ Z）

1＆gt; bankingdriver.obj：错误LNK2019：未解析的外部符号“public：void __thiscall Account :: setAccountNumber（int）”（？setAccountNumber @ Account @@ QAEXH @ Z）在函数“void __cdecl newRecord（class std：：basic_fstream＆gt;＆amp;）“（？newRecord @@ YAXAAV？$ basic_fstream @ DU？$ char_traits @ D @ std @@@ std @@@ Z）

1＆gt; BankingSystem.obj：错误LNK2001：未解析的外部符号“public：void __thiscall Account :: setAccountNumber（int）”（？setAccountNumber @ Account @@ QAEXH @ Z）

//banking system driver program

#include "BankingSystem.h" // Account class definition
#include <iostream>
#include <fstream>
#include <iomanip>
#include <cstdlib> // exit function prototype
using namespace std;



int enterChoice();
void createTextFile( fstream& );
void updateRecord( fstream& );
void newRecord( fstream& );
void deleteRecord( fstream& );
void outputLine( ostream&, const Account & );
int getAccount( const char * const );

enum Choices { PRINT = 1, UPDATE, NEW, DELETE, END };
int main()
{

   // open file for reading and writing
   fstream inOutCredit( "credit.dat", ios::in | ios::out | ios::binary );

   // exit program if fstream cannot open file
   if ( !inOutCredit ) 
   {
      cerr << "File could not be opened." << endl;
      exit ( 1 );
   } // end if

   int choice; // store user choice

   // enable user to specify action
   while ( ( choice = enterChoice() ) != END ) 
   {
      switch ( choice ) 
      {
         case PRINT: // create text file from record file
            createTextFile( inOutCredit );
            break;
         case UPDATE: // update record
            updateRecord( inOutCredit );
            break;
         case NEW: // create record
            newRecord( inOutCredit );
            break;
         case DELETE: // delete existing record
            deleteRecord( inOutCredit );
            break;
         default: // display error if user does not select valid choice
            cerr << "Incorrect choice" << endl;
            break;
      } // end switch

      inOutCredit.clear(); // reset end-of-file indicator
   } // end while
} // end main

// enable user to input menu choice
int enterChoice()
{
   // display available options
    std::cout << "\nEnter your choice" << endl
      << "1 - store a formatted text file of accounts" << endl
      << "2 - called \"print.txt\" for printing" << endl
      << "3 - update an account" << endl
      << "4 - add a new account" << endl
      << "5 - delete an account" << endl
      << "6 - end program\n? ";

   int menuChoice;
   std::cin >> menuChoice; // input menu selection from user
   return menuChoice;
} // end function enterChoice

// create formatted text file for printing
void createTextFile( fstream &readFromFile )
{
   // create text file
   ofstream outPrintFile( "print.txt", ios::out );

   // exit program if ofstream cannot create file
   if ( !outPrintFile ) 
   {
      cerr << "File could not be created." << endl;
      exit( 1 );
   } // end if

   outPrintFile << left << setw( 10 ) << "Account" << setw( 16 )
      << "Last Name" << setw( 11 ) << "First Name" << right
      << setw( 10 ) << "Balance" << endl;

   // set file-position pointer to beginning of readFromFile
   readFromFile.seekg( 0 );

   // read first record from record file
    Account client;
   readFromFile.read( reinterpret_cast< char * >( &client ),
      sizeof( Account ) );

   // copy all records from record file into text file
   while ( !readFromFile.eof() ) 
   {
      // write single record to text file
      if ( client.getAccountNumber() != 0 ) // skip empty records
         outputLine( outPrintFile, client );

      // read next record from record file
      readFromFile.read( reinterpret_cast< char * >( &client ), 
         sizeof( Account ) );
   } // end while
} // end function createTextFile

// update balance in record
void updateRecord( fstream &updateFile )
{
   // obtain number of account to update
   int accountNumber = getAccount( "Enter account to update" );

   // move file-position pointer to correct record in file
   updateFile.seekg( ( accountNumber - 1 ) * sizeof( Account ) );

   // read first record from file
   Account client;
   updateFile.read( reinterpret_cast< char * >( &client ), 
      sizeof( Account ) );

   // update record
   if ( client.getAccountNumber() != 0 ) 
   {
      outputLine( cout, client ); // display the record

      // request user to specify transaction
      std::cout << "\nEnter charge (+) or payment (-): ";
      double transaction; // charge or payment
      std::cin >> transaction;

      // update record balance
      double oldBalance = client.getBalance();
      client.setBalance( oldBalance + transaction );
      outputLine( cout, client ); // display the record

      // move file-position pointer to correct record in file
      updateFile.seekp( ( accountNumber - 1 ) * sizeof( Account ) );

      // write updated record over old record in file
      updateFile.write( reinterpret_cast< const char * >( &client ), 
         sizeof( Account ) );
   } // end if
   else // display error if account does not exist
      cerr << "Account #" << accountNumber 
         << " has no information." << endl;
} // end function updateRecord

// create and insert record
void newRecord( fstream &insertInFile )
{
   // obtain number of account to create
   int accountNumber = getAccount( "Enter new account number" );

   // move file-position pointer to correct record in file
   insertInFile.seekg( ( accountNumber - 1 ) * sizeof( Account ) );

   // read record from file
   Account client;
   insertInFile.read( reinterpret_cast< char * >( &client ), 
      sizeof( Account ) );

   // create record, if record does not previously exist
   if ( client.getAccountNumber() == 0 ) 
   {
      string lastName;
      string firstName;
      double balance;

      // user enters last name, first name and balance
      std:: cout << "Enter lastname, firstname, balance\n? ";
      std::cin >> lastName;
      std::cin >> firstName;
      std::cin >> balance;

      // use values to populate account values
      client.setLastName( lastName );
      client.setFirstName( firstName );
      client.setBalance( balance );
      client.setAccountNumber( accountNumber );

      // move file-position pointer to correct record in file
      insertInFile.seekp( ( accountNumber - 1 ) * sizeof( Account ) );

      // insert record in file                       
      insertInFile.write( reinterpret_cast< const char * >( &client ),
         sizeof( Account ) );                     
   } // end if
   else // display error if account already exists
      cerr << "Account #" << accountNumber
         << " already contains information." << endl;
} // end function newRecord

// delete an existing record
void deleteRecord( fstream &deleteFromFile )
{
   // obtain number of account to delete
   int accountNumber = getAccount( "Enter account to delete" );

   // move file-position pointer to correct record in file
   deleteFromFile.seekg( ( accountNumber - 1 ) * sizeof( Account ) );

   // read record from file
   Account client;
   deleteFromFile.read( reinterpret_cast< char * >( &client ), 
      sizeof( Account ) );

   // delete record, if record exists in file
   if ( client.getAccountNumber() != 0 ) 
   {
      Account blankClient; // create blank record

      // move file-position pointer to correct record in file
      deleteFromFile.seekp( ( accountNumber - 1 ) * 
         sizeof( Account ) );

      // replace existing record with blank record
      deleteFromFile.write( 
         reinterpret_cast< const char * >( &blankClient ), 
         sizeof( Account ) );

      std::cout << "Account #" << accountNumber << " deleted.\n";
   } // end if
   else // display error if record does not exist
      cerr << "Account #" << accountNumber << " is empty.\n";
} // end deleteRecord

// display single record
void outputLine( ostream &output,Account &record )
{
   output << left << setw( 10 ) << record.getAccountNumber()
      << setw( 16 ) << record.getLastName()
      << setw( 11 ) << record.getFirstName()
      << setw( 10 ) << setprecision( 2 ) << right << fixed 
      << showpoint << record.getBalance() << endl;
} // end function outputLine

// obtain account-number value from user
int getAccount( const char * const prompt )
{
   int accountNumber;

   // obtain account-number value
   do 
   {
       std::cout << prompt << " (1 - 100): ";
       std::cin >> accountNumber;
   } while ( accountNumber < 1 || accountNumber > 100 );

   return accountNumber;
} // end function getAccount

Answer 1

您应该检查'BankingSystem.h'和帐户类。有错误意味着这些函数解决了编译器找不到的'getBalance'，所以你应该首先检查这些函数是否存在，然后你必须确保你的项目中已经包含了BankingSystem.lib文件。

Answer 2

这些错误意味着定义了函数，但未声明。因此编译器已经看到了函数的定义，但函数尚未在项目中实现。也许它们存在于库中，或者您缺少项目中的CPP文件。

Answer 3

编译器获取源文件并生成目标文件。链接器获取所有目标文件（和库）并生成可执行文件（或DLL）。您收到的消息表明您忘记为这些函数编写代码，或者您忘记在链接步骤中包含必要的目标文件或库。

这似乎是MS VC ++。如果您正在使用命令行工具（或使用命令行工具的NMAKE之类的东西），那么请注意cl命令将默认编译然后尝试链接生成的文件。这适用于快速实验，但在项目跨多个源文件时很少有用。

我的猜测是你只是想编译一个文件，cl也试图为你链接它。要使cl只执行编译步骤，请使用/c选项。然后，一旦将所有源文件编译成目标文件，就可以将它们作为单独的步骤与link命令链接，并列出所有目标文件。

如果您使用Visual Studio IDE进行构建，则需要将所有源文件添加到同一个项目中。

LNK 2019和2001错误

3 个答案: