Basic char */const char* problem

**wisuzu** · 12-01-2011

I have a problem with some code
MyClass.h

Code:

public:
  //stuff

protected:
  // stuff
  char * path;
  //more stuff

   void function1();
   void function2();

};

MyClass.cc

Code:

//stuff

void MyClass::function1() {

      int spinvalue = 50;
      std::cout << "Parameter 1 = " << spinvalue << std::endl;
      std::cout << path << std::endl;
      //stuff
}


void MyClass::function2() 
{
  //stuff

  path = const_cast<char*> ( dialog.get_filename().c_str() );
      std::cout << "pathImagen = " << path << std::endl;

  //stuff
}

// more stuff
}

I need a char * in my function1(). I tried some possibilities, all envolving creating a new class variable (path).

I tried for this variable a char * path, char path[] ... and tried to convert the const char * in that, but for most i got a memory crash and for others i was not obtaining the value in function1().

I don't know what is wrong with it, but when i run function2() and function1() in this order i got :

1 pathImagen = /home/myhome/pathToImage/image.jpg
2 Parameter 1 = 50
3 �6� �

The 1, is the cout just after the const_cast<char*>, the 2 is the spinbutton working and the 3 is some random garbage :S

Anyone know what i'm doing wrong or know the way to do what i want? any lead/hint/help will be appreciated.

Thx in advance for all!

**R.Stiltskin** · 12-01-2011

It's hard to tell what your problem is from the little code you posted, but maybe this will help:

Code:

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

class A {

public:
    const char* str;
    
    void fun(const char* tmpstr) {
        str = tmpstr;
        cout << "str is " << str << endl;
    }
};


int main() {
    A myobj;
    string instr, instr2;
    cout << "enter a string: ";
    getline( cin, instr );
    myobj.str = instr.c_str();
    cout << "str is " << myobj.str << endl;
    
    cout << "enter another string: ";
    getline( cin, instr2 );
    myobj.fun(instr2.c_str() );
    return 0;
}

Good luck.

**MK27** · 12-01-2011

You must use either a real const char* (not a cast one, that is an illegal conversion) for this, or else a sufficiently sized char array and strcpy().

**wisuzu** · 12-01-2011

Edited

**wisuzu** · 12-01-2011

I answer it myself

the problem was that the memory that the pointer was pointing is free when the function ends, so i use a std::string as the variable in the header and then use path = std::string(dialog.get_filename().c_str()) and path.c_str() to access where i want
Solved

Thx to all the leads and hints!

**Elysia** · 12-01-2011

You don't need the ".c_str()".

**Salem** · 12-01-2011

If your class still contains a char * (or a const char *), then you're still doing it wrong.

Having a class member variable POINTING to something outside the class is a sure way to screw up at some point.

Make str a std::string str and the problem goes away.

**wisuzu** · 12-02-2011

Originally Posted by Salem

If your class still contains a char * (or a const char *), then you're still doing it wrong.

Having a class member variable POINTING to something outside the class is a sure way to screw up at some point.

Make str a std::string str and the problem goes away.

Yes, as i said finally the solution to the problem was creating a std::string class variable. Thx all the hints anyways!

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