fopen fclose in class constructor

bedoni · 03-24-2006, 09:20 AM

hi

I am getting an "[Linker Error] unresolved external 'fopen' referred from ...", when I want to use this function in the constructor of a class. I included stdio.h and there are other occasions of fopen (not in the constructor), which don't make problem. The parameter file_name is static, defined out of the class in a separate namespace. environment: borland C++ builder 5.

Does someone know something about this problem?

thanx bedoni

paulsm4 · 03-24-2006, 11:59 AM

Hi -

There should be no problem using "fopen()" in a constructor - or a destructor, or a class method, or anywhere else in any C++ program.

Please try this:
1. Write a simple, standalone C++ "hello world" (with an fopen in a constructor)
2. If it works, figure out what's different between your test program and your app
3. If it doesn't work, then post your code, and cut/paste the exact error message

I suspect the problem is a simple typo somewhere in your code...

'Hope that helps .. PSM

graemef · 03-24-2006, 02:24 PM

You probably want to include <stdio> rather than <stdio.h> But without seeing the code it's rather difficult to be sure.

paulsm4 · 03-24-2006, 04:08 PM

Hi -

This example "hello world" compiles, links and runs fine under both MS Visual C++ (Windows) and Gnu C++ (Suse Linux):

Code:

/*
 * x: test program calling stdio "fopen()" from a C++ constructor
 *
 * BUILD:
 * - GC++ 3.3.4:
 *   g++ -g -o x x.cpp
 * - MSVC++ 6.0:
 *   vcvars32
 *   cl -GX x.cpp
 *
 * SAMPLE OUTPUT:
 * C:\temp>x
 * Constructor: Successfully wrote file "x.txt"!
 * 
 * C:\temp>type x.txt
 * Hello from x!
 */
#include <stdio.h>
#include <iostream>

#if defined(WIN32)
  #include <windows.h>
  #define ERRNO GetLastError ()
#else
  #include <errno.h>
  #define ERRNO errno
#endif

class MyClass {
public:

  MyClass (const char *progname) 
  {
    FILE *fp = fopen ("x.txt", "w");
    if (fp != NULL)
    {
      fprintf (fp, "Hello from %s!\n", progname);
      fclose (fp);
      std::cout << "Constructor: Successfully wrote file \"x.txt\"!\n";
    }
    else
    {
      std::cout << "Unable to open file x.txt, errno: " << ERRNO << std::endl;
    }
  }

  ~MyClass () 
  {
    std::cout << "Done with MyClass..." << std::endl;
  }

};

int
main (int argc, char *argv[])
{
  MyClass *c = new MyClass (argv[0]);
  delete c;
  return 0;
}

addy86 · 03-24-2006, 04:29 PM

What compiler-/linker-options did you use?

bedoni · 03-25-2006, 10:20 AM

hi
thanks for replies, the code is spread in two files, one .h and one .cpp. (btw, in g++ i can compile, build and make (but not run, because of some other bug), so it might be borland-related shit.)

pile_engine.h:
--------------
#include <stdio.h>

namespace confined{
static char *full_path = NULL,
}

class pile_engine

ublic pile_access{public:

pile_engine( short P_MB,
unsigned char bits_for_QualifieRs,
P_interrupt_TYPE *interrupt,
char *path
); // Class Constructor
}

pile_engine.cpp:
----------------
pile_engine:

ile_engine
( short P_MB,
unsigned char bits_for_QualifieRs,
P_interrupt_TYPE *interrupt,
char *path )

{confined::full_path = new char[ path ];
FILE *F = fopen(confined::full_path, "r" );
bool Relational_Base_exists = ( F != NULL );
fclose(F);

if( Relational_Base_exists )
{STOP(); // take from HD
}
else
{ // create new
}
}

of course there is more code, but I pasted the relevant pieces, I think.

As for the compiler-/linker-options:

=>Compiler:
Code optimization: none
Warnings: selected
Debug Information: Y
Line nb. info... : Y
Disable inline expansions: Y
Pre-compiled Headers: none
Stack-frames: Y

=>Advanced Compiler:
Instruction set: Pentium Pro
Data alignment: Double word
Calling convention: C
Register variables: None
Output: Generate underscores
Floating Point: None
Langage compliance: Borland
Source: Identifier length(z): 250

=>C++:
Member pointers: Smallest
Honor member precision: Y
Zero length empty base classes: Y
Zero length empty class members: Y
Virtual tables: Y

=>Linker:
create debug info: Y
use dynamyc TRL: N
use debug libraries: N
Generate import library: Y
Don't generate state files: Y
max erros: 0
map file: off
warning: selected
min heap: 0x1000
max heap: 0x100000
image base: 0x100000
subsystem major: 4
subsystem minor: 0

Thanks, bedoni

paulsm4 · 03-25-2006, 01:10 PM

Hi -

Please use code tags when posting:

Code:

pile_engine.h:
--------------
#include <stdio.h>

namespace confined
{
  static char *full_path = NULL,
}

class pile_engine : public pile_access
{
public:

  pile_engine (short P_MB, unsigned char bits_for_QualifieRs, P_interrupt_TYPE *interrupt, char *path ); // Class Constructor
}

pile_engine.cpp:
----------------
pile_engine :: pile_engine (short P_MB, unsigned char bits_for_QualifieRs, P_interrupt_TYPE *interrupt, char *path )
{
  confined::full_path = new char[path];
  FILE *F = fopen (confined::full_path, "r" );
  bool Relational_Base_exists = (F != NULL);
  fclose (F);

  if (Relational_Base_exists)
  {
    STOP(); // take from HD
  }
  else
  {
    // create new
  }
}

And please post the linker message you get trying to compile this snippet.

Thanx in advance .. PSM

bedoni · 03-25-2006, 08:45 PM

The message I get is:

[Linker Error] Unresolved external 'fopen' referenced from E:\pile\easy_engine.obj
[Linker Error] Unresolved external 'fclose' referenced from E:\pile\easy_engine.obj

Thanks bedoni

paulsm4 · 03-25-2006, 10:20 PM

I'm surprised there isn't more to the message than that (an error number, for example).

But yes, it sounds like something in Borland C++ Builder 5 (quite old, as I'm sure you're aware).

SUGGESTIONS (if you still really want to get to the bottom of it):

1. Try the "hello world" approach I suggested (heck, cut/paste the "hello world" program I gave you). I'm sure you'll find the problem actually has nothing to do with calling "fopen()" in a constructor. My guess is it might instead have to do with your use of "namespace confined" and/or your parent class "pile_access" (which I don't believe you've shown us yet).

2. Set the Borland "generate mapfile" option to "ON".
This will give you vital clues.

3. Export your IDE configuration to a Borland makefile.

Acquaint yourself with bcc32.cfg and ilink32.cfg. They are your friends.

Experiment with the *order* in which you specify your libraries: it's critical.

4. Iterate between steps 1, 2 and 3; adding and removing stuff from your "hello world"
and adding and removing stuff from your .cfg and makefiles until you resolve the problem.

'Hope that helps .. PSM

bedoni · 03-26-2006, 10:25 AM

thank you for your explicit suggestions, I'll try it out - and let you know when I will get enlighted... (propably I'll get grey meanwhile

), thanks already, bedoni