Thread: Problems with c-style strings

Hey guys, hope some of you will help with this problem i have.

Code:

#ifndef ELEM_H
#define ELEM_H

#include <iostream>
#include <fstream>

using namespace std;

const int size=30;

class elem
{
public:
       elem();
       void setkey(int);
       int getkey();
       void setnext(int);
       int getnext();
       void setprev(int);
       int getprev();
       void setinfo(char *);
       void add(fstream &);       
private:
        int key;
        int next;
        int prev;
        char info[size];
};

elem::elem()
{
      key=next=prev=0;
	  for(int i=0;i<30;i++)
	  {
		  info[i]=' ';
	  }

}
         
void elem::setkey(int k)
{
     key=k;
}

int elem::getkey()
{
    return key;
}

void elem::setnext(int nex)
{
     next=nex;
}

int elem::getnext()
{
    return next;
}

void elem::setprev(int pre)
{
     prev=pre;
}

int elem::getprev()
{
    return prev;
}

void elem::setinfo(char * inf)
{
    for (int i=0;i<30;i++)
	{
		info[i]=inf[i];
	}
}

void elem::add(fstream &fout)
{
     fout.seekp(0,ios::end);
     fout.write((char*)&key,sizeof(int));
     fout.write(info,size);
     fout.write((char*)&prev,sizeof(int));
     fout.write((char*)&next,sizeof(int));
     fout.clear();
}

#endif

this is header

Code:

#include <iostream>
#include <fstream>
#include <cmath>
#include "elem.h"
#include <string>

using namespace std;                                                            

bool menu(int &);                                                               //menu lietotajam
int findPosNext(fstream &,int);                                                 //atrodam nakamo atslegu
int findPosPrev(fstream &,int);                                                 //atrodam iepriekseo atslegu
void initPoint(fstream &);                                                      //uzstadam nakamo uz ieprieksejo atslegu
void print(fstream &);                                                          //izdruka 
void printBack(fstream &);                                                      //izdruka 


int main()
{
    int ok=1,num=0,choice=1;
    char inff[30];
    string filen;

do{
cout<<"Enter the name of the file with an extension (.bin)\n";
cin>>filen;
 fstream f;

 f.open(filen.c_str(),ios::out|ios::in|ios::binary);
                                                                                //lietotais ievada faila nosaukumu
while(menu(choice))                                                             //izveidojam pec tam atveram failu
{                                                                               //kamer lietotais neievada -100
 switch(choice)
 {
       case 1:                                                                  //izveido objektu
            {elem obj1;                                                         //ieraksta atslegu un saturu
            cout<<"\nEnter the Key of record\n";
            cin>>num;
            obj1.setkey(num);
            cout<<"Enter the value of record\n";
            cin.getline(inff,30,'/0');
            obj1.setinfo(inff);
			obj1.add(f);                                                        //pievieno componentu failam
			initPoint(f);}                                                      //uzstada next un prev
			break;
		case 2:
			{print(f);}                                                         //izdruka
			break;
		case 3:
			{printBack(f);}                                                     //izdruka
			break;
}
}			
f.close();
cout<<"Procceed with new file? (1)  or exit (0) \n";                            //atkartosanas iespeja
cin>>ok;
}
while(ok!=0);
return 0;
}            
            
bool menu(int &choice)                                                          //lietotaja izvele
{
    cout<<"\nEnter your choice\n"
    <<"1 - to add a record to file\n"
    <<"2 - to print\n"
    <<"3 - to print backwards\n"
    <<"-100 to end this file proccessing\n";
    cin>>choice;
    return choice!=-100;
}

int findPosNext(fstream &f,int key)                                             //ejam caur failu
{                                                                               //meklejam vismazako starpibu starp divam key
    int next=0,cur,gap=32000;                                                   //un lai key butu mazak
	
	f.seekg(0,ios::beg);
    
    while(f)
    {
            f.read((char*)&cur,sizeof(int));
            if(fabs((double)cur-(double)key)<gap&&key<cur)
            {
					next=cur;
					gap=fabs((double)cur-(double)key);
			}        
            f.seekg(38,ios::cur);
	}
	f.clear();
	return next;                                                                //atgriezam next atslegu
}
	
int findPosPrev(fstream &f,int key)                                             //tas pats bet meklejam mazako starpibu
{                                                                               //un lai key butu mazak
    int prev=0,cur,gap=32000;
    
	f.seekg(0,ios::beg);
	
    while(f)
    {
            f.read((char*)&cur,sizeof(int));
            if(fabs((double)cur-(double)key)<gap&&key>cur)
            {
					prev=cur;
					gap=fabs((double)cur-(double)key);
			}        
            f.seekg(38,ios::cur);
	}
	f.clear();
	return prev;
}

void initPoint(fstream &f)                                                      //ejam caur failu
{                                                                               //atrodam katram key , nakamo atslegu
	int key=0,prev=0,next=0,pos=0;                                              //uzstadam to, katrai komponentei
	
	f.seekg(0,ios::beg);
	f.read((char*)&key,sizeof(int));
	
	while(f)
	{
		pos=f.tellg();
		prev=findPosPrev(f,key);
		next=findPosNext(f,key);
		f.seekp(pos+30,ios::beg);
		f.write((char*)&prev,sizeof(int));
		f.write((char*)&next,sizeof(int));
		f.seekg(pos+38,ios::beg);
		f.read((char*)&key,sizeof(int));
		
	}
f.clear();
}

void print(fstream &f)                                                          //ejam caur failu , atrodam mazako key
{                                                                               //drukam to , skatamies uz next
	int key=0,next=1,pos=0,small=32000;                                         //ejam caur failu , atrodam next , drukam to
    char inff[size];
    
    f.seekg(0,ios::beg);
	while(f)
	{
		f.read((char*)&key,sizeof(int));
		if(key<small) 
		{
			small=key;
			pos=f.tellg();
		}
		f.seekg(38,ios::cur);
	}
	f.clear();
	key=small;
	
	while(next!=0)
	{
		f.seekg(pos,ios::beg);
		cout<<key<<" ";
		f.read(inff,size);
		cout<<inff<<endl;
		f.seekg(4,ios::cur);
		f.read((char*)&next,sizeof(int));
		if(next!=0)
		{
                   f.seekg(0,ios::beg);
                   
                   while(f)
                   {
					f.read((char*)&key,sizeof(int));
					if(key==next)
					{
						pos=f.tellg();
						break;
					}
					f.seekg(38,ios::cur);
					}
					f.clear();
				
	}
}
f.clear();
}	
void printBack(fstream &f)                                                      //viss tas pats bet sakuma atrodam lielako key
{                                                                               //un pec meklejam prev
	int key=0,next=1,pos=0,small=0;
    char inff[size];
    
    f.seekg(0,ios::beg);
	while(f)
	{
		f.read((char*)&key,sizeof(int));
		if(key>small) 
		{
			small=key;
			pos=f.tellg();
		}
		f.seekg(38,ios::cur);
	}
	f.clear();
	
	while(next!=0)
	{
		f.seekg(pos,ios::beg);
		cout<<key<<" ";
		f.read(inff,size);
		cout<<inff<<endl;
		f.read((char*)&next,sizeof(int));
		if(next!=0)
		{
                   f.seekg(0,ios::beg);
                   
                   while(f)
                   {
					f.read((char*)&key,sizeof(int));
					if(key==next)
					{
						pos=f.tellg();
						break;
					}
					f.seekg(38,ios::cur);
					}
					f.clear();
				
	}
}
f.clear();
}

so basically , the problem is that, when i am reading input from user ( with cin>> , or cin.getline) the program takes the input and fills c-style string info with it( for example i input "asdasdasd", and program fills string with this information) , then it adds terminating symbol (/0) , and then , if there is some space unused, the program fills this space with ASCII representation of the byte 0xCC(found this at some website) , anyway , i don't know , how to get rid of it
any ideas?
p.s. when i am trying to output the content of string for example on the string , the program goes into infinite cycle and outputs this byte.

If you are using C-style strings, then it is completely irrelevant what bytes come after the \0 character. \0 ends the string, end of story.

so i checked with visual studio debugger
when i am creating class elem object in main( elem obj1 )
the data member info of object obj1 is filled with
[0] -52 'Ģ' char
this value for all array cells

when i am reading input with cin , all free cells are filled with this value

bump

Originally Posted by possik

so i checked with visual studio debugger
when i am creating class elem object in main( elem obj1 )
the data member info of object obj1 is filled with
[0] -52 'Ģ' char
this value for all array cells

when i am reading input with cin , all free cells are filled with this value

bump

That is entirely expected and normal and not anything to worry about.

Well, sort of. You using C-strings in a C++ program is definitely something to worry about. But once you have made that choice, those char arrays have to be filled with some character, and -52 is as good as anything else. If you are having difficulties, you will need to be more specific about where in your program those appear, and why.

Used auto formatter in codeblocks to help out :

Code:

#include <iostream>
#include <fstream>
#include <cmath>
#include "elem.h"
#include <string>

using namespace std;

bool menu(int &);                                                               //menu lietotajam
int findPosNext(fstream &,int);                                                 //atrodam nakamo atslegu
int findPosPrev(fstream &,int);                                                 //atrodam iepriekseo atslegu
void initPoint(fstream &);                                                      //uzstadam nakamo uz ieprieksejo atslegu
void print(fstream &);                                                          //izdruka
void printBack(fstream &);                                                      //izdruka


int main()
{
    int ok=1,num=0,choice=1;
    char inff[30];
    string filen;

    do
    {
        cout<<"Enter the name of the file with an extension (.bin)\n";
        cin>>filen;
        fstream f;

        f.open(filen.c_str(),ios::out|ios::in|ios::binary);
        //lietotais ievada faila nosaukumu
        while(menu(choice))                                                             //izveidojam pec tam atveram failu
        {
            //kamer lietotais neievada -100
            switch(choice)
            {
            case 1:                                                                  //izveido objektu
            {
                elem obj1;                                                         //ieraksta atslegu un saturu
                cout<<"\nEnter the Key of record\n";
                cin>>num;
                obj1.setkey(num);
                cout<<"Enter the value of record\n";
                cin.getline(inff,30,'/0');
                obj1.setinfo(inff);
                obj1.add(f);                                                        //pievieno componentu failam
                initPoint(f);
            }                                                      //uzstada next un prev
            break;
            case 2:
            {
                print(f);    //izdruka
            }
            break;
            case 3:
            {
                printBack(f);    //izdruka
            }
            break;
            }
        }
        f.close();
        cout<<"Procceed with new file? (1)  or exit (0) \n";                            //atkartosanas iespeja
        cin>>ok;
    }
    while(ok!=0);
    return 0;
}

bool menu(int &choice)                                                          //lietotaja izvele
{
    cout<<"\nEnter your choice\n"
        <<"1 - to add a record to file\n"
        <<"2 - to print\n"
        <<"3 - to print backwards\n"
        <<"-100 to end this file proccessing\n";
    cin>>choice;
    return choice!=-100;
}

int findPosNext(fstream &f,int key)                                             //ejam caur failu
{
    //meklejam vismazako starpibu starp divam key
    int next=0,cur,gap=32000;                                                   //un lai key butu mazak

    f.seekg(0,ios::beg);

    while(f)
    {
        f.read((char*)&cur,sizeof(int));
        if(fabs((double)cur-(double)key)<gap&&key<cur)
        {
            next=cur;
            gap=fabs((double)cur-(double)key);
        }
        f.seekg(38,ios::cur);
    }
    f.clear();
    return next;                                                                //atgriezam next atslegu
}

int findPosPrev(fstream &f,int key)                                             //tas pats bet meklejam mazako starpibu
{
    //un lai key butu mazak
    int prev=0,cur,gap=32000;

    f.seekg(0,ios::beg);

    while(f)
    {
        f.read((char*)&cur,sizeof(int));
        if(fabs((double)cur-(double)key)<gap&&key>cur)
        {
            prev=cur;
            gap=fabs((double)cur-(double)key);
        }
        f.seekg(38,ios::cur);
    }
    f.clear();
    return prev;
}

void initPoint(fstream &f)                                                      //ejam caur failu
{
    //atrodam katram key , nakamo atslegu
    int key=0,prev=0,next=0,pos=0;                                              //uzstadam to, katrai komponentei

    f.seekg(0,ios::beg);
    f.read((char*)&key,sizeof(int));

    while(f)
    {
        pos=f.tellg();
        prev=findPosPrev(f,key);
        next=findPosNext(f,key);
        f.seekp(pos+30,ios::beg);
        f.write((char*)&prev,sizeof(int));
        f.write((char*)&next,sizeof(int));
        f.seekg(pos+38,ios::beg);
        f.read((char*)&key,sizeof(int));

    }
    f.clear();
}

void print(fstream &f)                                                          //ejam caur failu , atrodam mazako key
{
    //drukam to , skatamies uz next
    int key=0,next=1,pos=0,small=32000;                                         //ejam caur failu , atrodam next , drukam to
    char inff[size];

    f.seekg(0,ios::beg);
    while(f)
    {
        f.read((char*)&key,sizeof(int));
        if(key<small)
        {
            small=key;
            pos=f.tellg();
        }
        f.seekg(38,ios::cur);
    }
    f.clear();
    key=small;

    while(next!=0)
    {
        f.seekg(pos,ios::beg);
        cout<<key<<" ";
        f.read(inff,size);
        cout<<inff<<endl;
        f.seekg(4,ios::cur);
        f.read((char*)&next,sizeof(int));
        if(next!=0)
        {
            f.seekg(0,ios::beg);

            while(f)
            {
                f.read((char*)&key,sizeof(int));
                if(key==next)
                {
                    pos=f.tellg();
                    break;
                }
                f.seekg(38,ios::cur);
            }
            f.clear();

        }
    }
    f.clear();
}
void printBack(fstream &f)                                                      //viss tas pats bet sakuma atrodam lielako key
{
    //un pec meklejam prev
    int key=0,next=1,pos=0,small=0;
    char inff[size];

    f.seekg(0,ios::beg);
    while(f)
    {
        f.read((char*)&key,sizeof(int));
        if(key>small)
        {
            small=key;
            pos=f.tellg();
        }
        f.seekg(38,ios::cur);
    }
    f.clear();

    while(next!=0)
    {
        f.seekg(pos,ios::beg);
        cout<<key<<" ";
        f.read(inff,size);
        cout<<inff<<endl;
        f.read((char*)&next,sizeof(int));
        if(next!=0)
        {
            f.seekg(0,ios::beg);

            while(f)
            {
                f.read((char*)&key,sizeof(int));
                if(key==next)
                {
                    pos=f.tellg();
                    break;
                }
                f.seekg(38,ios::cur);
            }
            f.clear();

        }
    }
    f.clear();
}

thx for sanitizing my code, bump

ok , maybe this is the source of the bug
in this function

Code:

void print(fstream &f)                                                          //ejam caur failu , atrodam mazako key
{
    //drukam to , skatamies uz next
    int key=0,next=1,pos=0,small=32000;                                         //ejam caur failu , atrodam next , drukam to
    char inff[size];

    f.seekg(0,ios::beg);
	pos=f.tellg();
    while(f)
    {
        f.read((char*)&key,sizeof(int));
        if(key<small)
        {
            small=key;
            pos=f.tellg();
        }
        f.seekg(38,ios::cur);
    }
    f.clear();
    key=small;

    while(next!=0)
    {
        f.seekg(pos,ios::beg);
        cout<<key<<" ";
        f.read(inff,size);
        cout<<inff<<endl;
        f.seekg(4,ios::cur);
        f.read((char*)&next,sizeof(int));
        if(next!=0)
        {
            f.seekg(0,ios::beg);

            while(f)
            {
                f.read((char*)&key,sizeof(int));
                if(key==next)
                {
                    pos=f.tellg();
                    break;
                }
                f.seekg(38,ios::cur);
            }
            f.clear();

        }
    }
    f.clear();
}

and in the almost similar function ( printBack )

the seekg() functions not working properly

so in the beginning of function in lines:

Code:

    char inff[size];

    f.seekg(0,ios::beg);
	pos=f.tellg();
    while(f)
    {

Code:

 f.seekg(0,ios::beg);

puts the get pointer to the -1 position, and i cannot enter the while cycle.

maybe this is the source of the bug ? (((

It's doubtful that seekg'ing to the beginning of the file could cause a problem (although I suppose you never know). You probably passed in a filestream that was in a bad state -- and no function works on a filestream that is in a bad state; you have to clear it first. So you should go back and see just when your filestream goes bad.

bump , still haven't found the solution to this problem ((

One of my greatest annoyances with C++ is how indistinct it is with file I/O errors.

Code:

#include <cstdio>
#include <errno.h>

fstream f;
f.open(filen.c_str(),ios::out|ios::in|ios::binary);
if (f.is_open() == false)
{
   std::perror( filen.c_str() );
}

I'm not positive this will help but does perror say anything is wrong?