John W. Colby
jwcolby at colbyconsulting.com
Mon Feb 21 18:42:38 CST 2005
I found c++ code for opening a pdf file and extracting the texst inside of
it. This is the only actual source code I've found for doing this. I am
not a c++ kinda guy and am wondering if anyone here can convert the code to
VB.net for me. It isn't too long (a few pages of code). If anyone thinks
they can do this let me know. No money available, just a challenge.
//This file contains extremely crude C source code to extract plain text
//from a PDF file. It is only intended to show some of the basics involved
//in the process and by no means good enough for commercial use.
//But it can be easily modified to suit your purpose. Code is by no means
//warranted to be bug free or suitable for any purpose.
//
//Adobe has a web site that converts PDF files to text for free,
//so why would you need something like this? Several reasons:
//
//1) This code is entirely free including for commericcial use. It only
// requires ZLIB (from www.zlib.org) which is entirely free as well.
//
//2) This code tries to put tabs into appropriate places in the text,
// which means that if your PDF file contains mostly one large table,
// you can easily take the output of this program and directly read it
// into Excel! Otherwise if you select and copy the text and paste it into
// Excel there is no way to extract the various columns again.
//
//This code assumes that the PDF file has text objects compressed
//using FlateDecode (which seems to be standard).
//
//This code is free. Use it for any purpose.
//The author assumes no liability whatsoever for the use of this code.
//Use it at your own risk!
//PDF file strings (based on PDFReference15_v5.pdf from www.adobve.com:
//
//BT = Beginning of a text object, ET = end of a text object
//5 Ts = superscript
//-5 Ts = subscript
//Td move to start next line
//No precompiled headers, but uncomment if need be:
#include "stdafx.h"
#include <stdio.h>
#include <windows.h>
//YOur project must also include zdll.lib (ZLIB) as a dependency.
//ZLIB can be freely downloaded from the internet, www.zlib.org
//Use 4 byte struct alignment in your project!
#include "zlib.h"
//Find a string in a buffer:
size_t FindStringInBuffer (char* buffer, char* search, size_t buffersize)
{
char* buffer0 = buffer;
size_t len = strlen(search);
bool fnd = false;
while (!fnd)
{
fnd = true;
for (size_t i=0; i<len; i++)
{
if (buffer[i]!=search[i])
{
fnd = false;
break;
}
}
if (fnd) return buffer - buffer0;
buffer = buffer + 1;
if (buffer - buffer0 + len >= buffersize) return -1;
}
return -1;
}
//Keep this many previous recent characters for back reference:
#define oldchar 15
//Convert a recent set of characters into a number if there is one.
//Otherwise return -1:
float ExtractNumber(const char* search, int lastcharoffset)
{
int i = lastcharoffset;
while (i>0 && search[i]==' ') i--;
while (i>0 && (isdigit(search[i]) || search[i]=='.')) i--;
float flt=-1.0;
char buffer[oldchar+5]; ZeroMemory(buffer,sizeof(buffer));
strncpy(buffer, search+i+1, lastcharoffset-i);
if (buffer[0] && sscanf(buffer, "%f", &flt))
{
return flt;
}
return -1.0;
}
//Check if a certain 2 character token just came along (e.g. BT):
bool seen2(const char* search, char* recent)
{
if ( recent[oldchar-3]==search[0]
&& recent[oldchar-2]==search[1]
&& (recent[oldchar-1]==' ' || recent[oldchar-1]==0x0d ||
recent[oldchar-1]==0x0a)
&& (recent[oldchar-4]==' ' || recent[oldchar-4]==0x0d ||
recent[oldchar-4]==0x0a)
)
{
return true;
}
return false;
}
//This method processes an uncompressed Adobe (text) object and extracts
text.
void ProcessOutput(FILE* file, char* output, size_t len)
{
//Are we currently inside a text object?
bool intextobject = false;
//Is the next character literal (e.g. \\ to get a \ character or \(
to get ( ):
bool nextliteral = false;
//() Bracket nesting level. Text appears inside ()
int rbdepth = 0;
//Keep previous chars to get extract numbers etc.:
char oc[oldchar];
int j=0;
for (j=0; j<oldchar; j++) oc[j]=' ';
for (size_t i=0; i<len; i++)
{
char c = output[i];
if (intextobject)
{
if (rbdepth==0 && seen2("TD", oc))
{
//Positioning.
//See if a new line has to start or just a
tab:
float num = ExtractNumber(oc,oldchar-5);
if (num>1.0)
{
fputc(0x0d, file);
fputc(0x0a, file);
}
if (num<1.0)
{
fputc('\t', file);
}
}
if (rbdepth==0 && seen2("ET", oc))
{
//End of a text object, also go to a new
line.
intextobject = false;
fputc(0x0d, file);
fputc(0x0a, file);
}
else if (c=='(' && rbdepth==0 && !nextliteral)
{
//Start outputting text!
rbdepth=1;
//See if a space or tab (>1000) is called
for by looking
//at the number in front of (
int num = ExtractNumber(oc,oldchar-1);
if (num>0)
{
if (num>1000.0)
{
fputc('\t', file);
}
else if (num>100.0)
{
fputc(' ', file);
}
}
}
else if (c==')' && rbdepth==1 && !nextliteral)
{
//Stop outputting text
rbdepth=0;
}
else if (rbdepth==1)
{
//Just a normal text character:
if (c=='\\' && !nextliteral)
{
//Only print out next character no
matter what. Do not interpret.
nextliteral = true;
}
else
{
nextliteral = false;
if ( ((c>=' ') && (c<='~')) ||
((c>=128) && (c<255)) )
{
fputc(c, file);
}
}
}
}
//Store the recent characters for when we have to go back
for a number:
for (j=0; j<oldchar-1; j++) oc[j]=oc[j+1];
oc[oldchar-1]=c;
if (!intextobject)
{
if (seen2("BT", oc))
{
//Start of a text object:
intextobject = true;
}
}
}
}
//int _tmain(int argc, _TCHAR* argv[])
int _tmain()
{
//Discard existing output:
FILE* fileo = fopen("c:\\pdf\\output2.txt", "w");
if (fileo) fclose(fileo);
fileo = fopen("c:\\pdf\\output2.txt", "a");
//Open the PDF source file:
FILE* filei = fopen("c:\\pdf\\somepdf.pdf", "rb");
if (filei && fileo)
{
//Get the file length:
int fseekres = fseek(filei,0, SEEK_END); //fseek==0 if ok
long filelen = ftell(filei);
fseekres = fseek(filei,0, SEEK_SET);
//Read ethe ntire file into memory (!):
char* buffer = new char [filelen]; ZeroMemory(buffer,
filelen);
size_t actualread = fread(buffer, filelen, 1 ,filei);
//must return 1
bool morestreams = true;
//Now search the buffer repeated for streams of data:
while (morestreams)
{
//Search for stream, endstream. We ought to first
check the filter
//of the object to make sure it if FlateDecode, but
skip that for now!
size_t streamstart = FindStringInBuffer (buffer,
"stream", filelen);
size_t streamend = FindStringInBuffer (buffer,
"endstream", filelen);
if (streamstart>0 && streamend>streamstart)
{
//Skip to beginning and end of the data
stream:
streamstart += 6;
if (buffer[streamstart]==0x0d &&
buffer[streamstart+1]==0x0a) streamstart+=2;
else if (buffer[streamstart]==0x0a)
streamstart++;
if (buffer[streamend-2]==0x0d &&
buffer[streamend-1]==0x0a) streamend-=2;
else if (buffer[streamend-1]==0x0a)
streamend--;
//Assume output will fit into 10 times input
buffer:
size_t outsize = (streamend -
streamstart)*10;
char* output = new char [outsize];
ZeroMemory(output, outsize);
//Now use zlib to inflate:
z_stream zstrm; ZeroMemory(&zstrm,
sizeof(zstrm));
zstrm.avail_in = streamend - streamstart +
1;
zstrm.avail_out = outsize;
zstrm.next_in = (Bytef*)(buffer +
streamstart);
zstrm.next_out = (Bytef*)output;
int rsti = inflateInit(&zstrm);
if (rsti == Z_OK)
{
int rst2 = inflate (&zstrm,
Z_FINISH);
if (rst2 >= 0)
{
//Ok, got something, extract
the text:
size_t totout =
zstrm.total_out;
ProcessOutput(fileo, output,
totout);
}
}
delete[] output; output=0;
buffer+= streamend + 7;
filelen = filelen - (streamend+7);
}
else
{
morestreams = false;
}
}
fclose(filei);
}
if (fileo) fclose(fileo);
return 0;
}
John W. Colby
www.ColbyConsulting.com
Contribute your unused CPU cycles to a good cause:
http://folding.stanford.edu/