Thread: gggrrr, unknown problem with <fstream>

k, i'm gonna paste a bunch of code in here cause i'm not sure what is causing this to generate errors. my problem apears to be in
void pkrEdit::export(string file)

if i compile and run exfile gets written to 0 bytes, however if i single step the program it produces and access violation at the line of code

ifAllPkr.read((char *)&buffer, FStruct[i].data_len1);

hope someone can help with this.


main.cpp

Code:

#include "pkr.h"


int main()
{
	pkrEdit pk;
	string *dirs;
	string *files;
	ofstream test;
	test.open("test.txt", ios::binary | ios::app);
	files = new string[pk.numfiles];
	dirs = new string[pk.numdirs];
	pk.GetDirs(dirs);
	pk.GetFiles(files);
    pk.export(files[20]);
}

pkr.cpp

Code:

#include "pkr.h"

pkrEdit::pkrEdit()
{

	ifAllPkr.open("ALL.PKR", ios::binary | ios::ate);

	ifAllPkr.seekg(0, ios::beg);

	ifAllPkr.read((char *)&HStruct, sizeof(HStruct));

	DStruct = new PK_DIR_STRUC[HStruct.num_dirs];    //create an array of dir_structs and file_structs
	FStruct = new PK_FILE_STRUC[HStruct.num_files];  //= the number of dirs and files

	for(int i = 0; i < HStruct.num_dirs; i++)        //and populate said arrays
	{
		ifAllPkr.read((char *)&DStruct[i], sizeof(PK_DIR_STRUC));
	}

	for(i = 0; i < HStruct.num_files; i++)
	{
		ifAllPkr.read((char *)&FStruct[i], sizeof(PK_FILE_STRUC));
	}
	numfiles = HStruct.num_files;
	numdirs = HStruct.num_dirs;

//	ofAllPkr.open("ALL.PKR", ios::binary | ios::ate);
//	ofAllPkr.seekp(0, ios::beg);
}

string * pkrEdit::GetDirs(string *dirs)
{

	for(int i = 0; i < HStruct.num_dirs; i++)
	{
	
		dirs[i] = DStruct[i].path;

	}
	return(dirs);

}

string * pkrEdit::GetFiles(string *files)
{
	for(int i = 0; i < HStruct.num_files; i++)
	{
		files[i] = FStruct[i].name;
	}
	return(files);
}

void pkrEdit::import(char *oldFile, char *newfile)
{}

void pkrEdit::export(string file)
{
	char *buffer;
	for(int i = 0; i < HStruct.num_files; i++)
	{
		if(file == FStruct[i].name)
		{
            ifAllPkr.seekg(FStruct[i].data_offset);
			buffer = new char[FStruct[i].data_len1];
			ifAllPkr.read((char *)&buffer, FStruct[i].data_len1);
			exFile.open(file.c_str(), ios::binary | ios::ate);
			exFile.write(buffer, FStruct[i].data_len1);
			exFile.close();
			delete[] buffer;
		}
	}
}

pkr.h

Code:

#include <fstream>
#include <string>
#include <iostream>

using namespace std;

typedef struct PK_HEAD_STRUC
{
	char ident[4];
	int unknown;// always 1
	int num_dirs;
	int num_files;
}
PK_HEAD;

typedef struct PK_DIR_STRUC
{
	char path[32];
	int file_offset;
	int file_count;
}
PK_DIR;

typedef struct PK_FILE_STRUC
{
	char name[32];
	int unknown; // always -2
	int data_offset;
	int data_len1;
	int data_len2; // always == data_len2
}
PK_FILE;


class pkrEdit 
{
public:
	int numfiles;
	int numdirs;
    pkrEdit();
	string *GetDirs(string *dirs);
	string *GetFiles(string *files);
	void import(char *oldFile, char *newFile);
	void export(string file);

protected:
	PK_HEAD_STRUC HStruct;
	PK_DIR_STRUC *DStruct;
	PK_FILE_STRUC *FStruct;
private:
	ofstream exFile;
	ifstream imFile;
	ofstream ofAllPkr;
	ifstream ifAllPkr;

	
};

ps. thanks in advance for any help.
btw, i know i still need to go back and cleanup a lot of the memory i allocated just havn't got around to it yet

>>ifAllPkr.read((char *)&buffer, FStruct[i].data_len1);
Try:
>>ifAllPkr.read((char *)buffer, FStruct[i].data_len1);
Note the lack of &

still the same, after single steping some more and shuffling some code around i've found that the problem is partialy realated to

FStruct[i].data_len1

as in

ifAllPkr.read((char *)&buffer, FStruct[i].data_len1);

i have verified that FStruct[I].data_len1 is a valid integer
and is being read properly in the class constructor.
so why it should generate an error is beyond me.

however, i have noticed that if i replace all the references
to FStruct[i].data_len1 and replace them with integers such as

ifAllPkr.read((char *)&buffer, 500);

then the read operation is succesfull but
i then get another access violation from
the exfile.open() statement.

hope that made some sense , this has been driving me mad all day

[edit]
after playing around with it a bit more i found that removing the & does kind of work however, the first 120,000 someodd bytes of the output file are blank, after that everything is hunky dorey.
any ideas?
[/edit]

success!!! but i'm at a loss as to explain why.
so here's my revised code if anyone cares to take a crack at
telling me why one works and not the other i'd really aprieciate it.

new code

Code:

void pkrEdit::export(string file)
{
	char *buffer;
	for(int i = 0; i < HStruct.num_files; i++)
	{
		if(file == FStruct[i].name)
		{
		         ifAllPkr.seekg(FStruct[i].data_offset, ios::beg);
			buffer = new char[FStruct[i].data_len1];
			ifAllPkr.read((char *)buffer, FStruct[i].data_len1);
			cout<<FStruct[i].data_len1;
			exFile.open("file.c_str()", ios::binary | ios::ate);
			exFile.write((char *)buffer, FStruct[i].data_len1);
                           exFile.close();
			delete[] buffer;
		}
	}
}

old code

Code:

void pkrEdit::export(string file)
{
     char *buffer;
     for(int i = 0; i < HStruct.num_files; i++)
    {
          if(file == FStruct[i].name)
         {
                ifAllPkr.seekg(FStruct[i].data_offset);
                buffer = new char[FStruct[i].data_len1];
                ifAllPkr.read((char *)&buffer, FStruct[i].data_len1);
                exFile.open(file.c_str(), ios::binary | ios::ate);
                exFile.write(buffer, FStruct[i].data_len1);
                exFile.close();
                delete[] buffer;
           }
      }
}

hey, thanks for the help


grrr, gotta start looking over my code more carefully before i post though

exFile.open("file.c_str()", ios::binary | ios::ate);

for a minute there i was thinking that fstream couldn't accept
file.c_str so i just quickly enclosed it in quotes to see if it would would accept a normal string or if there was something else wrong there. but i forgot to get rid of the quotes when i was done. embarassing

anyway thanks once again to both of you for helping me out.