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What's wrong with this strcpy and this pointer

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What's wrong with this strcpy and this pointer

Feb 18th, 2007

Hello
I'm trying to assign a value from a string via some pointer, but I got an error and I cannot figure how to solve it.
Do you have an idea? I would really help me. The problematic line is marked between *********
Thanks.

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
// reading a text file
#include <iostream>
#include <fstream>
#include <string>
using namespace std;
 
 
struct Cours
{
    char *sigle;
    Cours *suivant;
};
 
struct Etudiant
{
    char *nom;
    Etudiant *apres;
};
 
struct Professeur
{
    char nom [20];
    Professeur *suivant;
};
 
 
class DossierProfesseur
{        
    public:
        Professeur *tete;
        DossierProfesseur();
        ~DossierProfesseur();
        void affichage();
};
 
 
DossierProfesseur::DossierProfesseur()
{
    Professeur *PCourant, *PTete;
    string line;
    ifstream myfile ("FP.txt");
    if (myfile.is_open())
    {
        while (! myfile.eof() )
        {
            getline (myfile,line);
            cout << line << endl;
            PCourant = new Professeur;
/*****************************************************/
            strcpy (PCourant->nom, line);
/*****************************************************/
        }
        myfile.close();
    }
 
    else cout << "Unable to open file";
}
 
 
void main () {
 
 
    DossierProfesseur *dossierProfesseur;
 
    dossierProfesseur= new DossierProfesseur;
}
// reading a text file
#include <iostream>
#include <fstream>
#include <string>
using namespace std;


struct Cours
{
    char *sigle;
    Cours *suivant;
};

struct Etudiant
{
    char *nom;
    Etudiant *apres;
};

struct Professeur
{
    char nom [20];
    Professeur *suivant;
};


class DossierProfesseur
{        
    public:
        Professeur *tete;
        DossierProfesseur();
        ~DossierProfesseur();
        void affichage();
};


DossierProfesseur::DossierProfesseur()
{
    Professeur *PCourant, *PTete;
    string line;
    ifstream myfile ("FP.txt");
    if (myfile.is_open())
    {
        while (! myfile.eof() )
        {
            getline (myfile,line);
            cout << line << endl;
            PCourant = new Professeur;
/*****************************************************/
            strcpy (PCourant->nom, line);
/*****************************************************/
        }
        myfile.close();
    }

    else cout << "Unable to open file";
}


void main () {
 

    DossierProfesseur *dossierProfesseur;
    
    dossierProfesseur= new DossierProfesseur;
}

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iamthwee

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Re: What's wrong with this strcpy and this pointer

Feb 18th, 2007

http://www.cplusplus.com/reference/c...ng/strcpy.html

Last edited by iamthwee; Feb 18th, 2007 at 4:47 pm.

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Re: What's wrong with this strcpy and this pointer

Feb 18th, 2007

Thanks iamthwee, but it is not helping me a lot, I was in that page before writing this post and I did what I understood:

strcpy (where-the-data-will-be, where-there-are-now)

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
strcpy (PCourant->nom, line);
strcpy (PCourant->nom, line);

Last edited by earlyriser; Feb 18th, 2007 at 4:56 pm.

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Re: What's wrong with this strcpy and this pointer

Feb 18th, 2007

>> strcpy (PCourant->nom, line);

line is a c++ class, strcpy() wants a c style pointer. You have to use std::string's c_str method to get the pointer, like this
strcpy (PCourant->nom, line.c_str());

 Help with Code Tags 
 c Syntax (Toggle Plain Text) 
struct Professeur
{
    char nom [20];
    Professeur *suivant;
};
struct Professeur
{
    char nom [20];
    Professeur *suivant;
};

Since you are writing a c++ program you should use c++ std::string class, not character arrays, unless your teacher requires you to use character arrays. Using std::string will make your life a lot easier and eleminate several problems with using strcpy() and other similar standard c string handling functions. The main problem with those functions is they will allow you to scribble all over memory by copying strings beyond the allocation of the destination buffer. Example: copy a 25 character string into that buffer that has only room for 19 characters plus null terminator. After that happens your program will likely crash at some point and you will spend hours trying to find the problem.

Last edited by Ancient Dragon; Feb 18th, 2007 at 5:03 pm.

Don't PM me with questions -- you might get a nasty PM in response. If you have a question then post it in one of the forums.

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Join Date: Aug 2005

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iamthwee

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Re: What's wrong with this strcpy and this pointer

Feb 18th, 2007

yeah and don't forget to clean up after with delete[], avoid void main and EOF blah blah blah.

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Re: What's wrong with this strcpy and this pointer

Feb 18th, 2007

Thanks Ancient Dragon!
It works, well, the program doesnt, but at least the strcpy works.
My teacher wants char arrays.

Thanks iamthwee!

Last edited by earlyriser; Feb 18th, 2007 at 5:34 pm.

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Re: What's wrong with this strcpy and this pointer

Feb 18th, 2007

After reading a line in a text file I need to read another line which contains an INT. I thought that the bold line in this code will be ok to retreive the data, but it doesnt.

Help with Code Tags

(Toggle Plain Text)

            
#include <iostream>
#include <fstream>
#include <string>
#include <cstdlib>
using namespace std;

struct Professeur
{
    char nom[20];
    int ancien;
};


class DossierProfesseur
{
   
        
    public:
        Professeur *tete;
        DossierProfesseur();
        ~DossierProfesseur();
};


DossierProfesseur::DossierProfesseur()
{
    Professeur *PCourant, *PTete=NULL;
    string line;
    ifstream myfile ("FP.txt");
    if (myfile.is_open())
    {
        while (! myfile.eof() )
        {
            getline (myfile,line);
            PCourant = new Professeur;
            strcpy (PCourant->nom, line.c_str());
            cout << PCourant->nom;
            getline (myfile, PCourant->ancien);
        }
        myfile.close();
    }

    else cout << "Unable to open file";
}


void main () {
 

    DossierProfesseur *dossierProfesseur;
    
    dossierProfesseur= new DossierProfesseur;
}

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John A

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Re: What's wrong with this strcpy and this pointer

Feb 18th, 2007

You're trying to use getline() to read a string into an integer. It just ain't going to work. Read it into a string, and take it out with atoi() or use a stringstream.

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
std::string line;
std::stringstream lineStream;
getline(myFile, line);
lineStream << line;
lineStream >> PCourant->ancien;
std::string line;
std::stringstream lineStream;
getline(myFile, line);
lineStream << line;
lineStream >> PCourant->ancien;

Your code is driving me crazy! If you're going to use char arrays, you might as well be using C. And no, I know it's not your fault, so I blame your teacher for that.

"Technological progress is like an axe in the hands of a pathological criminal."

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Re: What's wrong with this strcpy and this pointer

Feb 18th, 2007

Thanks joeprogrammer!
I will try that and give the feedback tomorrow, (I have been doing this homework all the day).
I didn't know that C is better for char arrays than C++.

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John A

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Re: What's wrong with this strcpy and this pointer

#10

Feb 18th, 2007

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Originally Posted by earlyriser

Thanks joeprogrammer!
I will try that and give the feedback tomorrow, (I have been doing this homework all the day).
I didn't know that C is better for char arrays than C++.

It's better because C functions were designed for char arrays. A lot of C++ functions were designed for std::string. You could always use the old C functions to manipulate the mix of C and C++ strings, but you usually shouldn't mix C and C++ functions unless it's absolutely necessary.

"Technological progress is like an axe in the hands of a pathological criminal."