I'm really unfamiliar with the grabber and reading bytes from file and I need to get a .pcx pictur from a compacted file with this definition:
from byte x to y file offset where PCX data is located
from byte x' to y' length of pcx data in byte

For those who know I want to extract BITMAP *'s from .sff and .fnt file format form Elecbyte's Mugen (http://www.elecbyte.com) to make an utility.

Thank's a lot for any help.

In the allegro/src directory is a file called "pcx.c". It contains the pcx reading / loading code. What you need to do is to copy that file into your project and then change it slightly.
(Like skipping to the position of the pcx in the file)

I'm working on it.
This is my class:

class spriteObj{
   public:
      spriteObj();
      ~spriteObj();
      spriteObj* searchSprite(int,int);

      BITMAP* img;
      int groupNo, imgNo;
      int x, y;
      PALETTE ownPal;
      bool samePal;
      bool hasPreviousCopy;
      spriteObj* next;
};

And the code is there:
<code>
spriteObj::spriteObj(){
x=y=0;
groupNo=imgNo=0;
img=NULL;
next=NULL;
hasPreviousCopy=false;
}

spriteObj::~spriteObj(){
if(img!=NULL&&!hasPreviousCopy)destroy_bitmap(img);
if(next!=NULL)delete next;
}

spriteObj* spriteObj::searchSprite(int inGroupNo, int inImgNo){
if(groupNo==inGroupNo&&imgNo==inImgNo) return this;
if(next!=NULL)return next->searchSprite(inGroupNo,inImgNo);
return NULL;
}

spriteObj* load_sff(char* directory, const char* filename){
FILE* infile;
char newFilename[256];
strcpy(newFilename,directory);
strcpy(newFilename+strlen(directory),filename);
spriteObj* Head=NULL;

char signature[12];
char ver[4];
int noOfGroup;
int noOfImg;
int offsetOfFirstFile;
int sizeOfSubheader;
char palType;
char blank[3];
char comment[476];

int offsetOfNextSubfile;
int subfileLength;
int xCoord,yCoord;
int unsigned groupNo;
int unsigned imgNo;
int unsigned indexOfPreviousCopy;
bool samePal;
char imgBlank[14];
PALETTE pal;

int xmin,ymin,width,height,bpp,bytes_per_line;
BITMAP *tmpBitMap;
int sizeCount;
bool gotPal=false;
PALETTE previousPal;

_fmode=O_BINARY;
if((infile=fopen(newFilename,"r"))!=NULL){
printf("loadinf file %s...\n",newFilename);
fread(signature,12,1,infile);
fread(ver,4,1,infile);
fread(&noOfGroup,4,1,infile);
fread(&noOfImg,4,1,infile);
fread(&offsetOfFirstFile,4,1,infile);
fread(&sizeOfSubheader,4,1,infile);
fread(&palType,1,1,infile);
fread(blank,3,1,infile);
for(int i=0;i<476;i++)comment<i>=getc(infile);

/*printf("\nsignture: %s\n", signature);
printf("version: %d%d%d%d\n", ver[0], ver[1], ver[2], ver[3]);
printf("no of group: %d\n", noOfGroup);
printf("no of img: %d\n", noOfImg);
printf("offset of first subheader: %d\n", offsetOfFirstFile);
printf("size of subheader: %d\n", sizeOfSubheader);
printf("palette type: %d\n", palType);
printf("blank: %s\n", blank);
printf("comment: %s\n", comment);*/

Head = new spriteObj;
spriteObj* current = Head;
for(int i=0;i<noOfImg;i++){
tmpBitMap=NULL;
xmin=ymin=width=height=bytes_per_line=0;
xCoord=yCoord=groupNo=imgNo=indexOfPreviousCopy=0;

fread(&offsetOfNextSubfile,4,1,infile);
fread(&subfileLength,4,1,infile);
fread(&xCoord,2,1,infile);
if(xCoord&0x00008000)xCoord-=65536;
fread(&yCoord,2,1,infile);
if(yCoord&0x00008000)yCoord-=65536;;
fread(&groupNo,2,1,infile);
fread(&imgNo,2,1,infile);
fread(&indexOfPreviousCopy,2,1,infile);
fread(&samePal,1,1,infile);
fread(blank,13,1,infile);
sizeCount=subfileLength;
if(/*indexOfPreviousCopy==0*/subfileLength!=0){
for(int i=0;i<4;i++)fgetc(infile);
fread(&xmin,2,1,infile);
fread(&ymin,2,1,infile);
fread(&width,2,1,infile);
fread(&height,2,1,infile);
width+=1-xmin;
height+=1-ymin;
for(int i=0;i<53;i++)fgetc(infile);
bpp=fgetc(infile)*8;
fread(&bytes_per_line,2,1,infile);
for(int i=0;i<60;i++)fgetc(infile);

tmpBitMap = create_bitmap_ex(bpp,width-xmin+1,height-ymin+1);

sizeCount-=128;
if(bpp == 8){
for(int liney=0;liney<height;liney++){
int linex=0, linexx=0;
while(linex<bytes_per_line){
char ch=fgetc(infile);
sizeCount--;
int c=0;
if(0xc0 == (0xc0&ch)){
c=(ch&0x3f);
ch=fgetc(infile);
sizeCount--;
}else c=1;
while (c--) {
if (linex < tmpBitMap->w)
tmpBitMap->line[liney][linex] = ch;
linex++;
}
}
}

if(!samePal){
while(sizeCount>0){
fgetc(infile);
sizeCount--;
if(sizeCount==768){
for(int i=0;i<256;i++){
current->ownPal<i>.r=(int)fgetc(infile)/4;
current->ownPal<i>.g=(int)fgetc(infile)/4;
current->ownPal<i>.b=(int)fgetc(infile)/4;
sizeCount-=3;
}
current->ownPal[0].r=63;
current->ownPal[0].g=0;
current->ownPal[0].b=63;

if(!gotPal||palType==0){
previousPal=current->ownPal;
gotPal=true;
}
break;
}
}
}else{
current->ownPal = previousPal;
}
}
}else{
spriteObj* tmpPointer=Head;
for(int i=0;i<indexOfPreviousCopy&&tmpPointer->next!=NULL;i++){
tmpPointer=tmpPointer->next;
}
tmpBitMap = tmpPointer->img;
current->ownPal = tmpPointer->ownPal;
current->hasPreviousCopy = true;
}
if(palType==1)for(;sizeCount>0;sizeCount--)fgetc(infile);
else if(samePal){fgetc(infile);sizeCount--;}
/* printf("\noffset of next subfile: %d\n", offsetOfNextSubfile);
printf("subfile length: %d\n", subfileLength);
printf("axis x coord: %d\n", xCoord);
printf("axis y coord: %d\n", yCoord);
printf("group no.: %d\n", groupNo);
printf("image no.: %d\n", imgNo);
printf("index of previous copy: %d\n", indexOfPreviousCopy);
printf("same palette: %s\n", (samePal)?"true":"false");
printf("xmin: %d\n",xmin);
printf("ymin: %d\n",xmin);
printf("width: %d\n",width);
printf("height: %d\n",height);
printf("bpp: %d\n",bpp);
printf("bytes_per_line: %d\n",bytes_per_line);
printf("byte leave: %d\n", sizeCount);
system("PAUSE"); */
current->x = xCoord;
current->y = yCoord;
current->img = tmpBitMap;
current->groupNo = groupNo;
current->imgNo = imgNo;
current->next = new spriteObj;
current = current->next;
}

fclose(infile);
current = Head;
if(current->next != NULL){
while(current->next->next != NULL)current=current->next;
delete current->next;
current->next = NULL;
}
}else printf("\ncan't open file %s\n",newFilename);
_fmode=O_TEXT;
printf("load finish.\n");
return Head;
}
<code>

This work fine for 8bits pcx since the newest version doesn't support 16bits sprites.