我正在尝试编写这个程序，将员工数据库保存在随机访问文件中，它必须具有添加员工和删除员工的功能（通过写入记录中的所有空格）。这是我到目前为止所做的，但它不能正常工作。在阅读员工时，它会读取正确记录的工资，但会记录下一条记录的名称。此外，当我删除最后一条记录并在该记录中添加员工时，我无法查看员工信息，我收到异常错误。
我不是在寻找解决方案，只是在正确的方向上轻推。感谢。
#include "stdafx.h"
#include <iostream>
#include <iomanip>
#include <fstream>
#include <sstream>
#include "ccc_empl.h"
using namespace std;
const int NEWLINE_LENGTH = 2;
const int RECORD_SIZE = 30 + 10 + NEWLINE_LENGTH;
/**
converts a string to a floating-point value
@param s a string representing a floating-point value
@return the equivalent floating-point value
*/
double string_to_double(string s)
{
istringstream instr(s);
double x;
instr >> x;
return x;
}
/*
reads an employee record from the input file
@param e the employee
@param in the file to read from
*/
Employee read_employee(istream& in)
{
string line;
getline(in, line);
string input_name = line.substr(0, 30);
double input_salary = string_to_double(line.substr(30, 10));
Employee e(input_name, input_salary);
return e;
}
/*
gets input for an Employee object
@param input_name the name of the employee
@param input_salary the salary of the employee
@param e the Employee object
@return returns the Employee object
*/
Employee input_employee()
{
string input_name;
cout << "Name: ";
cin.ignore();
getline(cin, input_name);
cout << "Salary: ";
double input_salary;
cin >> input_salary;
Employee e(input_name, input_salary);
return e;
}
/**
adds an employee record to a file
@param e the employee record to write
@param out the file to write to
*/
void add_employee(Employee e, ostream& out)
{
out << e.get_name()
<< setw(30)
<< fixed << setprecision(2)
<< e.get_salary();
}
/**
removes an employee record from a file
@param e the employee record to remove
@param out the file to remove from
*/
void remove_employee(ostream& out)
{
out << " " << setw(42) << fixed << setprecision(2) << " \n";
}
int main()
{
cout << "Please enter the data file name: ";
string filename;
cin >> filename;
fstream fs;
fs.open(filename);
fs.seekg(0, ios::end); // Go to end of file
int nrecord = fs.tellg() / RECORD_SIZE; // determine number of records in the file
int menu_input = 0;
string input_name;
double input_salary = 0;
while (menu_input != 4)
{
cout << "Please enter the record to update: (0 - " << nrecord - 1 << ") exit to quit ";
int pos = 0;
cin >> pos;
if(cin.fail())
{
cout << "Exiting..." << endl;
system("pause");
return 0;
}
// menu for user input
cout << "\nWhat action would you like to perform?" << endl;
cout << "Add employee.....1" << endl;
cout << "Remove employee..2" << endl;
cout << "View employee....3" << endl;
cin >> menu_input;
switch(menu_input)
{
case 1: fs.seekg(pos * RECORD_SIZE, ios::beg);
add_employee(input_employee(), fs);
break;
case 2: fs.seekg(pos * RECORD_SIZE, ios::beg);
remove_employee(fs);
break;
case 3: fs.seekg(pos * RECORD_SIZE, ios::beg);
cout << "\nName: " << read_employee(fs).get_name() << "Salary: " << read_employee(fs).get_salary() << endl << endl;
break;
default: cout << "Invalid entry" << endl;
break;
}
}
fs.close();
system("pause");
return 0;
}
好的，这是新的和改进的（好吧，我想是的）代码。我唯一的问题是当添加一个员工时，我可以让程序将它添加到第一个打开的记录就好了，但是如果没有打开的记录，我似乎无法将它添加到最后文件没有搞乱添加到第一个空记录。我的意思是，如果有空记录，它会将员工添加到记录中，但如果没有空记录，则不会将员工添加到文件末尾。如果我添加代码添加到文件末尾，则会发生以下两种情况之一：要么添加到空记录，要么请求另一名员工并将其添加到结尾，或者只是跳过空记录并添加到文件的结尾。
不确定我在这里做错了什么，但任何提示都会受到赞赏。
#include "stdafx.h"
#include <iostream>
#include <iomanip>
#include <fstream>
#include <sstream>
#include "ccc_empl.h"
using namespace std;
const int NEWLINE_LENGTH = 2;
const int RECORD_SIZE = 30 + 10 + NEWLINE_LENGTH;
/**
converts a string to a floating-point value
@param s a string representing a floating-point value
@return the equivalent floating-point value
*/
double string_to_double(string s)
{
istringstream instr(s);
double x;
instr >> x;
return x;
}
/*
reads an employee record from the input file
@param e the employee
@param in the file to read from
*/
Employee read_employee(istream& in)
{
string line;
getline(in, line);
string input_name = line.substr(0, 30);
double input_salary = string_to_double(line.substr(30, 10));
Employee e(input_name, input_salary);
return e;
}
/*
gets input for an Employee object
@param input_name the name of the employee
@param input_salary the salary of the employee
@param e the Employee object
@return returns the Employee object
*/
Employee input_employee()
{
string input_name;
cout << "Name: ";
cin.ignore();
getline(cin, input_name);
cout << "Salary: ";
double input_salary;
cin >> input_salary;
Employee e(input_name, input_salary);
return e;
}
/**
adds an employee record to a file
@param e the employee record to write
@param out the file to write to
*/
void add_employee(Employee e, ostream& out)
{
out << e.get_name()
<< setw(10 + 30 - e.get_name().length())
<< fixed << setprecision(2)
<< e.get_salary() << "\n";
}
/**
removes an employee record from a file
@param e the employee record to remove
@param out the file to remove from
*/
void remove_employee(ostream& out)
{
out << " " << setw(40) << fixed << setprecision(2) << " \n";
}
int main()
{
cout << "Please enter the data file name: ";
string filename;
cin >> filename;
fstream fs;
fs.open(filename);
fs.seekg(0, ios::end); // Go to end of file
int nrecord = fs.tellg() / RECORD_SIZE; // determine number of records in the file
int menu_input = 1;
string input_name;
double input_salary = 0;
while (menu_input)
{
// menu for user input
cout << "\nWhat action would you like to perform?" << endl;
cout << "Add employee.....1" << endl;
cout << "Remove employee..2" << endl;
cout << "View employee....3" << endl;
cout << "Exit.............4" << endl;
cin >> menu_input;
if (menu_input == 4)
{
cout << "\nExiting..." << endl << endl;
system("pause");
return 0;
}
// switch statment to perform selected menu_input task
switch(menu_input)
{
case 1: // adds an employee in the first empty record
// or at the end of the file if no records are empty
{
int count = 0;
string s;
for (int i = 0; i < nrecord; i++)
{
fs.seekp(count, ios::beg);
getline(fs, s);
if (isspace(s[0]))
{
fs.seekp(count, ios::beg);
add_employee(input_employee(), fs);
nrecord++;
break;
}else
count += 42;
}
}
break;
case 2: {
cout << "Please enter the record to remove: (0 - " << nrecord -1 << ") ";
int pos = 0;
cin >> pos;
fs.seekp(pos * RECORD_SIZE, ios::beg);
remove_employee(fs);
}
break;
case 3: {
cout << "Please enter the record to view: (0 - " << nrecord -1 << ") ";
int pos = 0;
cin >> pos;
fs.seekg(pos * RECORD_SIZE, ios::beg);
Employee e(read_employee(fs));
cout << "\nName: " << e.get_name() << "Salary: " << e.get_salary() << endl << endl;
}
break;
default: cout << "Invalid entry" << endl;
break;
}
}
fs.close();
system("pause");
return 0;
}
答案 0 :(得分：1)
您拨打read_employee(fs)两次。首先读取你想要的记录，第二个读取下一个记录（标准没有指定它们中的哪个是'第一个'）。
答案 1 :(得分：0)
似乎你永远不会在add_employee中添加行终止符，并且read_employee会被调用两次。只需缓存函数的结果。
我知道这只是作业，但我认为你可以改进这个程序。
需要数据库在运行时保留为文件吗？您可以将整个文件读入Employee数组并在最后重写它。它不会限制员工姓名的长度。
此程序不是跨平台的。您不应该依赖文件大小来确定数据库中的条目数，因为行终止符因操作符而异。相反，请全部阅读，并计算条目。
只有Windows有“暂停”程序。要达到同样的效果，只需读取stdin并在程序结束时忽略输入。