segmentation fault reading an image

ramako (36)
Hi guys, I'm trying to load an image into a buffer, but it gives a segmentation fault. Here's the code

main: 
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#include "imagen.h"
#include "codificar.h"
#include "imagenES.h"
using namespace std;

int main (int argc, char** argv) {

Imagen test(512,512);
test.leerimagen(argv[1]);
}


class private 
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      private:
              int fil,col;
              unsigned char **buffer;


Constructor: 
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Imagen::Imagen(int filas,int columnas) {
 fil=filas;
 col=columnas;
 buffer=new unsigned char*[fil];
 for (int i=0; i<fil; i++)
     buffer[i]=new unsigned char[col];
}


reading image

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bool Imagen::leerimagen(const char file[]){ // se puede saber con antelacion fil y col???
return LeerImagenPGM(file,fil,col,*buffer);

}


function of reading an image

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bool LeerImagenPGM (const char nombre[], int& filas, int& columnas, unsigned char buffer[])
{
  bool exito= false;
  filas=0;
  columnas=0;
  ifstream f(nombre);
  
  if (LeerTipo(f)==IMG_PGM)
    if (LeerCabecera (f, filas, columnas))
	if (f.read(reinterpret_cast<char *>(buffer),filas*columnas))
	  exito= true;
  
  return exito;
}


I am sure that LeerImagenPGM is working ok (actually it is not I who did that function so that's why I am positive that's not the function that gives the segfault, lol).

The image IS actually 512 x 512.
Last edited on
webJose (2948)
The buffer is wrong. It should be:

unsigned char *buffer = new unsigned char[fil * col];
ramako (36)
The buffer must be a matrix. It is a requirement. and must be done that way (pointer to pointers).
Moschops (7244)
Compile it with debugging symbols in, run it under a debugger, and know exactly on which line and with what values the segFault occurs.
Last edited on
ramako (36)
Well, thank you, I was afraid of using DDD because I kinda had a trauma with it :P But it was quite easy to use and I found the segfault was....the destructor.

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Imagen::~Imagen() {

delete[] buffer;



}


Well, quite the suprise for me..

Moschops (7244)
As ye sow new, so shall ye reap delete.

Something like this, possibly. I don't often allocate arrays of pointers to arrays, so I could well have this a bit wrong.

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// Allocate
buffer=new unsigned char*[fil];
 for (int i=0; i<fil; i++)
     buffer[i]=new unsigned char[col];
.
.
.
.
// deallocate
 for (int i=0; i<fil; i++)
   delete[] buffer[i];
 delete[] buffer;


Alternatively, use a C++ container such as vector and you won't have to worry about it :)
Last edited on
ramako (36)
This is what it returns me, after coding the destructor that way.

*** glibc detected *** ./ocultar: double free or corruption (!prev): 0x0000000001384020 ***
======= Backtrace: =========
/lib/libc.so.6(+0x774b6)[0x7fc41fa094b6]
/lib/libc.so.6(cfree+0x73)[0x7fc41fa0fc83]
./ocultar[0x401c48]
./ocultar[0x400fa3]
/lib/libc.so.6(__libc_start_main+0xfe)[0x7fc41f9b0d8e]
./ocultar[0x400e79]
======= Memory map: ========
00400000-00403000 r-xp 00000000 08:03 544528                             /home/


And it keeps going in the memory map, too long to post it.
I'll try to look more into it later since I have to go now.

Thanks for your help!
Moschops (7244)
Yes, that was a bit of a hacked together stab in the dark at it!

If you don't want to use vectors, you might find it easier you to use a single array of size fil*col to store all the pixels. It'll be much simpler to allocate, deallocate and use.
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