multiline注释 * /到位时，该程序运行良好，而while循环不属于该程序。
，但是，如果我删除 / * * /并将WAIL循环带入程序并尝试添加新联系人，则输出为
Contact added
nocy，联系实际上并未添加。这种故障的原因是什么？
完整程序如下：
#include <fstream>
#include <iostream>
#include <iomanip>
#include <cstring>
#define length 30
using namespace std;
fstream file, file_temp;
char * cistrstr (char *, char *);
class contact
{
char name[length];
char number[length];
public:
void newcontact (void);
void updatecontact (void);
void searchphone (void);
void searchname (void);
void deletecontact (void);
void display (void);
};
void contact :: newcontact(void)
{
contact c;
int m = 0;
cout << "Enter name: ";
cin.ignore (1, '\n');
cin.getline (name, length);
/*
while (1)
{
file.seekg (m * sizeof (contact), ios :: beg);
file.read ((char *) & c, sizeof (c));
if (file.eof() == 1)
break;
if (strcmp (c.name, name) == 0)
{
cout << "\nContact already exists.\nChoose another name or use the \"update contact\" option\n";
return;
}
m++;
}*/
strcpy (c.name, name);
cout << "Enter phone: ";
cin >> c.number;
file.seekg(0, ios::end);
file.write ((char *) & c, sizeof (c));
cout << "\nContact added\n";
}
void contact :: updatecontact(void)
{
int update_choice, m = 0;
contact c;
cout << "\nEnter 1 to update name, enter 2 to update contact number\n";
cin >> update_choice;
file.seekg(0, ios :: beg);
if (update_choice == 1)
{
cout << "\nEnter phone number: ";
cin >> number;
cout << "Enter new name: ";
cin.ignore (1, '\n');
cin.getline (name, length);
}
else if (update_choice == 2)
{
cout << "\nEnter name: ";
cin.ignore (1, '\n');
cin.getline (name, length);
cout << "Enter new phone number: ";
cin >> number;
}
else
cout << "\nInvalid option\n";
while (1)
{
file.seekg (m * sizeof (contact), ios :: beg);
file.read ((char *) & c, sizeof (c));
if ((update_choice == 1 && strcmp (c.number, number) == 0) || (update_choice == 2 && strcmp (c.name, name) == 0))
{
strcpy (c.name, name);
strcpy (c.number, number);
file.seekg (m * sizeof (contact), ios :: beg);
file.write ((char *) & c, sizeof (c));
cout << "\nContact updated\n";
break;
}
if (file.eof() == 1)
{
cout << "\nContact not found\n";
break;
}
m++;
}
}
void contact :: searchphone(void)
{
contact c;
int m = 0, found = 0;
file.seekg(0, ios ::beg);
cout << "\nEnter name: ";
cin >> name;
while (1)
{
file.seekg (m * sizeof (contact), ios :: beg);
file. read ((char *) & c, sizeof (c));
if (file.eof() == 1)
break;
if (cistrstr(c.name, name) != 0)
{
cout << setw(30) << left << c.name << setw(10) << c.number << endl;
found = 1;
}
m++;
}
if (found == 0)
cout << "\nContact not found\n";
}
void contact :: searchname(void)
{
contact c;
int m = 0, found = 0;
file.seekg(0, ios :: beg);
cout << "\nEnter number: ";
cin >> number;
while (1)
{
file.seekg (m * sizeof (contact), ios :: beg);
file.read ((char *) & c, sizeof (c));
if (file.eof() == 1)
break;
if (cistrstr(c.number, number) != NULL)
{
cout << setw(30) << left << c.name << setw(10) << c.number << endl;
found = 1;
}
m++;
}
if (found == 0)
cout << "\nContact not found\n";
}
void contact :: deletecontact (void)
{
contact c;
int i = 0;
cout << "\nEnter name of contact to be deleted: ";
cin >> name;
file_temp.open("data_temp", ios ::app);
file_temp.close();
file_temp.open ("data_temp", ios :: in | ios :: out);
while (1)
{
file.read ((char *) &c, sizeof (contact));
if (file.eof () == 1)
break;
if (strcmp (c.name, name) != 0)
file_temp.write ((char *) &c, sizeof (contact));
else
{
cout << "Contact deleted";
i = 1;
}
}
if (i == 0)
cout << "Contact not found";
file.close();
file_temp.close();
remove ("data");
rename ("data_temp", "data");
}
void contact :: display (void)
{
char c;
file.seekg (0, ios::end);
int end = file.tellg(), m = 0;
file.seekg (0, ios::beg);
while (1)
{
contact c;
file.read ((char *) & c, sizeof (c));
cout << setw(30) << left << c.name << setw(10) << c.number << endl;
if (file.tellg() == -1 ||file.tellg() == end)
break;
m++;
}
}
int main()
{
char another = 'Y';
int choice, update_return;
contact c;
file.open("data", ios ::app);
file.close();
while (another == 'Y' || another == 'y')
{
file.open("data", ios ::in | ios ::out);
cout << "\033[2J\033[1;1H";
cout << "\n\nMAKE A CHOICE...\n\n";
cout << "1. Add a new contact\n";
cout << "2. Update a contact\n";
cout << "3. Search a phone number (using name)\n";
cout << "4. Search a name (using phone number)\n";
cout << "5. Delete a contact\n";
cout << "6. Display entire list\n\n";
cin >> choice;
switch (choice)
{
case 1:
c.newcontact();
break;
case 2:
c.updatecontact();
break;
case 3:
c.searchphone();
break;
case 4:
c.searchname();
break;
case 5:
c.deletecontact();
break;
case 6:
c.display();
break;
default:
cout << "\nInvalid option\n";
}
file.close();
cout << "\nWant to try again? (Y/N)...\n";
cin >> another;
}
return 0;
}
char * cistrstr (char *string, char *substring)
{
int i, j, l_string, l_sub;
l_string = strlen (string);
l_sub = strlen (substring);
char *p, *a, *b;
a = (char *) malloc (l_string + 1);
b = (char *) malloc (l_sub + 1);
for (i = 0; string[i] != '\0'; i++)
{
if (string[i] > 96 && string[i] < 123)
a[i] = string[i] - 32;
else
a[i] = string [i];
}
a[i] = '\0';
for (i = 0; substring[i] != '\0'; i++)
{
if (substring[i] > 96 && substring[i] < 123)
b[i] = substring[i] - 32;
else
b[i] = substring[i];
}
b[i] = '\0';
for (i = 0; a[i] != '\0'; i++)
{
if (a[i] == b[0])
{
p = &string[i];
for (j = 0; b[j] != '\0'; j++)
{
if (b[j] != a[i + j])
break;
}
if (b[j] == '\0')
{
free (a);
free (b);
return p;
}
}
}
free (a);
free (b);
return NULL;
}
错误是由于以下事实引起的：如果您将文件读取到文件末尾（如在段循环中），这会导致文件处于错误状态。这意味着随后的写入失败。答案是在您进行写入之前清除错误状态，例如
if (file.eof() == 1)
{
file.clear();
break;
}
的起点和结束