Question

Question on replacing existing functions with a wrapper.

Asked by: ankurshri

I have a wrapper written for malloc and realloc(they take different signatures as malloc but do the same thing). I need to use this function in existing code which uses malloc. Is there a way in C where i can 'alias' as in unix parlance, my wrapper, whenever the compiler encounters a malloc function. That is, my wrapper should be used whenever a malloc or realloc function is encountered.

Any help will be greatly appreciated.

Regards,
Ankur

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Asked On
2003-02-06 at 20:53:40ID20503938
Tags

c

,

malloc

Topic

C Programming Language

Participating Experts
2
Points
75
Comments
10

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Answers

 

by: zebadaPosted on 2003-02-06 at 21:49:42ID: 7900639

Use #define

Assume your replacement for malloc is
void *ualloc(int size,int otherparm);
If you specify
#define malloc(s) ualloc(s,123)
then the precompiler will change all instances of malloc to ualloc.
Do the same type of thing for realloc.

Regards
Paul

 

by: ankurshriPosted on 2003-02-07 at 01:05:13ID: 7901285

The problem i am facing is,
my function looks something like this:

char *memalloc(int,char *,int)
{
..
..
..
malloc(size);
..
..
}

now in main, i call
main()
{
p3=memalloc(size,__file__,__line__);
}

now in my header.h, i define,

#define malloc() (memalloc())

The problem i am facing is, in my memalloc function,i am calling malloc. This "malloc" call also seems to get replaced by memalloc, while inside the memalloc function itself. So is there anyway i can get around this?

TIA
Ankur

 

by: zebadaPosted on 2003-02-07 at 02:26:58ID: 7901870

Although not very elegant (I hope a more elegant solution exists - anyone?), you could just place your memalloc function at the bottom of a C source file and #undef malloc just prior to it like this:

#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <memory.h>

#define malloc(a) memalloc(a,__FILE__,__LINE__)

// _________________________________________________________________________
int
main(int argc, char *argv[])
{
  char *s;

  s = malloc(100);
  free(s);
  return 0;
}

// _________________________________________________________________________
void *
memalloc(int size, char *f, int l)
{
#undef malloc
  return malloc(size);
}

 

by: ankurshriPosted on 2003-02-07 at 03:14:28ID: 7902079

But still a preprocessor will not be able to undef at compile time. THe undef does not seems to work!
Is there any other way out?
Ankur

 

by: ankurshriPosted on 2003-02-07 at 03:19:03ID: 7902097

But still a preprocessor will not be able to undef at compile time. THe undef does not seems to work!
Is there any other way out?
Ankur

 

by: ankurshriPosted on 2003-02-07 at 05:33:00ID: 7902800

This will not work becaue malloc is not preprossor directive its a function. If u give some other name other than malloc like xmalloc it is working.
Is overriding is possible in c. Means can i use my malloc as well as library malloc in different places in a same file suppose x.c.
Thanks

 

by: zebadaPosted on 2003-02-07 at 11:14:50ID: 7905216

What compiler are you using - I tested it using VC++ and it works OK.

This sorce code:

#define malloc(a) memalloc(a,__FILE__,__LINE__)

void *memalloc(int size, char *f, int l);

// _________________________________________________________________________
int
main(int argc, char *argv[])
{
  char *s;

  s = malloc(100);
  free(s);
  return 0;
}

// _________________________________________________________________________
void *
memalloc(int size, char *f, int l)
{
#undef malloc
  return malloc(size);
}


after the pre-compiler executes becomes this source code:

void *memalloc(int size, char *f, int l);


int
main(int argc, char *argv[])
{
  char *s;

  s = memalloc(100,"d:\\mystuff\\vc++\\nullterm\\nullterrm.c",108);
  free(s);
  return 0;
}


void *
memalloc(int size, char *f, int l)
{

  return malloc(size);
}

 

by: zebadaPosted on 2003-02-07 at 11:16:17ID: 7905222

By the way,
I used the /P option (Project->Settings->C/C++, Project Options) to only run the precompiler and produce the <file>.i preprocessor output.

 

by: jmcgPosted on 2003-12-19 at 20:01:59ID: 9976461

Nothing has happened on this question in over 10 months. It's time for cleanup!

My recommendation, which I will post in the Cleanup topic area, is to
accept answer by zebada.

Please post any comments here within the next seven days.

PLEASE DO NOT ACCEPT THIS COMMENT AS AN ANSWER!

jmcg
EE Cleanup Volunteer

20120131-EE-VQP-002

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