c++ - 随机字符进入我用c++写的文件

Question

#include <string.h>
#include <conio.h>
#include <fstream.h>
#include <string.h>



class mobile
{
int id;
float price;
char *model,*brand;
public:
int getId()
{
    return id;
}
float getPrice(){return price;}
mobile()
{
    brand = new char[5];
    model = new char[5];
    id = 0;
    price = 0.0;
}
void addDetail()
{
    cout<<"\nEnter the mobile ID ";cin>>id;
    cout<<"\nEnter the Price of mobile ";cin>>price;
    cout<<"\nEnter the Brand name of mobile ";cin>>brand;
    cout<<"\nEnter the Model of mobile ";cin>>model;
    ofstream file("database.txt",ios::app);
    char c=' ',n='\n';
    file<<id<<c;
    file<<price<<c;
    file<<brand<<c;
    file<<model<<n;
    file.close();

}

char* getbrand(){return brand;}
char* getModel(){return model;}
~mobile()
{
    delete brand;
    delete model;
}

};

void count()
{
int counter = 0;
char c;
ifstream file("database.txt");
file.seekg(0,ios::beg);
if(!file)cout<<"File not present";
while(file)
{
    file.get(c);
    if(c == '\n')
    {
        counter++;
    }
}
cout<<"The no of entries "<<counter;
file.close();
}

void addMobile()
{
char *model,*brand;

mobile m;
m.addDetail();    
}

void EditMobile()
{
fstream file;
char* brand,*model;
file.open("database.txt",ios::in);
brand = new char;
model = new char;
char c;
int id,pos;
float price;
float f;
if(!file)cout<<"File not present";
else
{


file>>id;cout<<"ID :"<<id<<endl;
file>>price;cout<<"Price :"<<price<<endl;
file>>brand;cout<<"Brand :"<<brand<<endl;
file>>model;cout<<"Model :"<<model<<endl;

}

delete brand;
delete model;
file.close();

}

void admin()
{

char* userpassword;
userpassword = new char;
char* pass;
pass = new char;

cout<<"\n\nEnter the Password";
cin>>userpassword;
fstream fin;
fin.open("password.txt",ios::in | ios::out);
if(!fin)
cout<<"\n\nFile does not exist";
else
{
fin>>pass;
if(strcmp(userpassword,pass) == 0)
{
    char ch;

    count();
    clrscr();
    cout<<"\n\nAcces Granted!!\n\n\tWelcome";
    cout<<"\n\n1.Add a Mobile.";
    cout<<"\n2.Edit a Mobile.";
    cout<<"\n3.Delete a Mobile.";
    cout<<"\n4.View the Database.\n\nEnter Your Choice ";
    ch = getch();
    switch(ch)
    {
    case '1':
        addMobile();
        break;
    case '2':
        EditMobile();
        break;
    case '3':
        //deleteMobile();
        break;

    }
}
else
{
    cout<<"\n\nAcces Denied";
    return;
}
}

fin.close();
delete userpassword;
}
int main()
{
char choice;
clrscr();
cout<<"Welcome to Mobile Store management Program";
cout<<"\n1.Find a Mobile.";
cout<<"\n2.Know Price.";
cout<<"\n3.Know Description.";
cout<<"\n4.Administrator Login.\n\nEnter Your Choice";
choice = getch();
switch(choice)
{
case '1':

    break;
case '4':
    admin();
    break;
}
getch();
return 0;
}

现在在我输入的输出中:

Acces Granted!!

        Welcome

1.Add a Mobile.
2.Edit a Mobile.
3.Delete a Mobile.
4.View the Database.

Enter Your Choice
Enter the mobile ID 1

Enter the Price of mobile 123.34

Enter the Brand name of mobile Nokia

Enter the Model of mobile mynokiamobile

我在 database.txt 文件中得到的输出是:

1 123.339996 Nokia mynoki   ile

中间的空格是这里看不到的随机字符。

Answer 1

您超出了分配给 brand 和 Model 的内存范围。

brand = new char[5];
model = new char[5];

brand 和 mobile 分配了 5 个字节的内存，但您的输入比这更长。

您输入的值是:
brand:6 字节长的“Nokia”(5 + 1 附加字节为 NULL 终止符)&
对于 model:“mynokiamobile”，长度为 14 字节

这会导致未定义的行为。
您需要增加这些自由存储(堆)分配。

更好的 C++ 方法是使用 std::string 而不是字符数组，但我不知道这似乎是一项家庭作业练习，也许你不允许使用它们，在我看来这会很蹩脚。