Programming Forums > Application Development > C++

davidguygc · Dec 6th, 2005, 11:28 PM

Hey, I'm stuck on this code for a project of mine. I need to create a PGM struct that takes in a filename, reads the type, # of columns, # of rows, and max val, followed by the bulk of the data. It takes in the filename and opens it, and does fine until the loop that reads in the bulk of the data. It changes the pgm.filename variable for no reason I can see:

(Toggle Plain Text)

PGM open(bool &file_opened)
{
	PGM file;
	int x;
	
	cout << "File name? ";
	cin >>  file.filename;
	string filename = file.filename;
	if(file.filename == "") throw 2;

	ifstream ifs(filename.c_str());
	ifs >> file.type >> file.col >> file.row >> file.max;
	if(!ifs) throw 1;
	else
	{
		//getting the int's
		for(x = 0; x < (file.col * file.row); x++)
		{
			cout << x +1 << ". " << file.filename << endl;
                        system("pause");
			ifs >> file.bulk[x];
		}

I have it cout the filename every cycle so I can see when it starts to change the name, and after about 10 iterations, it starts to warp the filename.
Here is the code for the struct:

(Toggle Plain Text)

struct PGM
{
	int max, row, col;
	string filename, type;
	int* bulk;
	string* readable;
	PGM();
	PGM(string filename, int type, int maxval, int row, int col);
};

the code was changing the filename before I added in the cout. It crashes right after that when it tries to read the file, but can't find the file.
Any ideas?
Thanks,
---David

grumpy · Dec 7th, 2005, 2:55 AM

You haven't provided enough information, but I'm guessing that you haven't initialised the pointer file.bulk to point at anything useful. A consequence of that is that the line (in the loop)

(Toggle Plain Text)

    ifs >> file.bulk[x];

will tromp on random memory.

After the line;

(Toggle Plain Text)

   ifs >> file.type >> file.col >> file.row >> file.max;

you need to add a line something like;

(Toggle Plain Text)

   file.bulk = new int[file.col*file.row];

That will stop the immediate crash, but won't prevent other problems. For example, you will also need to hand-roll a copy constructor (and operator=()) for the PBM type as well.

DaWei · Dec 7th, 2005, 8:12 AM

This is just another way of saying something Grumpy said, to emphasize the point. Those two thangys down ther are like your address book. There you may put directions on where to find someone, but you can't actually make those someones live in your address book. You need to go build a couple houses and put the ADDRESSES there.

(Toggle Plain Text)

	int* bulk;
	string* readable;

davidguygc · Dec 7th, 2005, 9:05 PM

I'm fairly sure that is what is wrong with the code, this project is about creating dynamic memory and pointers. My only problem now is that when I try to compile it, two functions I have in a header that I created, say that there are multiple definitions of it. I have the header (console.h) nested in another header (include.h), that is then in my main header, (header.h). In each header I put in

(Toggle Plain Text)

#ifndef filename_h_
#define filename_h_

blah blah

#endif

The really big thing that's making me scratch my head is the fact that it was compiling just fine without those errors appearing, then one time i compiled the project it gave me that error, and has been ever since. I am using Dev-C++, and I tried putting all the files in a new project, but same problem. Any suggestions?

DaWei · Dec 7th, 2005, 9:45 PM

Quote:

two functions I have in a header

This has been covered about a half-dozen times in the last two weeks. Don't put code in a header file. The reasons are plentiful, and so are the recent threads explaining them. I recommend a search and some research.

Dec 6th, 2005, 11:28 PM	#1
davidguygc Programmer Join Date: Mar 2005 Location: Lubbock, TX Posts: 30 Rep Power: 0	Code is changing a variable that isn't involved Hey, I'm stuck on this code for a project of mine. I need to create a PGM struct that takes in a filename, reads the type, # of columns, # of rows, and max val, followed by the bulk of the data. It takes in the filename and opens it, and does fine until the loop that reads in the bulk of the data. It changes the pgm.filename variable for no reason I can see: (Toggle Plain Text) PGM open(bool &file_opened) { PGM file; int x; cout << "File name? "; cin >> file.filename; string filename = file.filename; if(file.filename == "") throw 2; ifstream ifs(filename.c_str()); ifs >> file.type >> file.col >> file.row >> file.max; if(!ifs) throw 1; else { //getting the int's for(x = 0; x < (file.col * file.row); x++) { cout << x +1 << ". " << file.filename << endl; system("pause"); ifs >> file.bulk[x]; } PGM open(bool &file_opened) { PGM file; int x; cout << "File name? "; cin >> file.filename; string filename = file.filename; if(file.filename == "") throw 2; ifstream ifs(filename.c_str()); ifs >> file.type >> file.col >> file.row >> file.max; if(!ifs) throw 1; else { //getting the int's for(x = 0; x < (file.col * file.row); x++) { cout << x +1 << ". " << file.filename << endl; system("pause"); ifs >> file.bulk[x]; } I have it cout the filename every cycle so I can see when it starts to change the name, and after about 10 iterations, it starts to warp the filename. Here is the code for the struct: (Toggle Plain Text) struct PGM { int max, row, col; string filename, type; int* bulk; string* readable; PGM(); PGM(string filename, int type, int maxval, int row, int col); }; struct PGM { int max, row, col; string filename, type; int* bulk; string* readable; PGM(); PGM(string filename, int type, int maxval, int row, int col); }; the code was changing the filename before I added in the cout. It crashes right after that when it tries to read the file, but can't find the file. Any ideas? Thanks, ---David

Dec 7th, 2005, 2:55 AM	#2
grumpy Programming Guru Join Date: Jun 2005 Location: Adelaide, South Australia Posts: 1,260 Rep Power: 5	You haven't provided enough information, but I'm guessing that you haven't initialised the pointer file.bulk to point at anything useful. A consequence of that is that the line (in the loop) (Toggle Plain Text) ifs >> file.bulk[x]; ifs >> file.bulk[x]; will tromp on random memory. After the line; (Toggle Plain Text) ifs >> file.type >> file.col >> file.row >> file.max; ifs >> file.type >> file.col >> file.row >> file.max; you need to add a line something like; (Toggle Plain Text) file.bulk = new int[file.colfile.row]; file.bulk = new int[file.colfile.row]; That will stop the immediate crash, but won't prevent other problems. For example, you will also need to hand-roll a copy constructor (and operator=()) for the PBM type as well.

Dec 7th, 2005, 8:12 AM	#3
DaWei Resident Grouch Join Date: Jun 2005 Posts: 6,453 Rep Power: 10	This is just another way of saying something Grumpy said, to emphasize the point. Those two thangys down ther are like your address book. There you may put directions on where to find someone, but you can't actually make those someones live in your address book. You need to go build a couple houses and put the ADDRESSES there. (Toggle Plain Text) int* bulk; string* readable; int* bulk; string* readable; __________________ Abstraction doesn't make it impossible to write bad code; it makes it possible to write superior code. Contributor's Corner: Grumpy on C++ Exceptions DaWei on Pointers

Dec 7th, 2005, 9:05 PM	#4
davidguygc Programmer Join Date: Mar 2005 Location: Lubbock, TX Posts: 30 Rep Power: 0	Thanks, I'm fairly sure that is what is wrong with the code, this project is about creating dynamic memory and pointers. My only problem now is that when I try to compile it, two functions I have in a header that I created, say that there are multiple definitions of it. I have the header (console.h) nested in another header (include.h), that is then in my main header, (header.h). In each header I put in (Toggle Plain Text) #ifndef filename_h_ #define filename_h_ blah blah #endif #ifndef filename_h_ #define filename_h_ blah blah #endif The really big thing that's making me scratch my head is the fact that it was compiling just fine without those errors appearing, then one time i compiled the project it gave me that error, and has been ever since. I am using Dev-C++, and I tried putting all the files in a new project, but same problem. Any suggestions?

Thread Tools
Show Printable Version Email this Page
Display Modes
Linear Mode Switch to Hybrid Mode Switch to Threaded Mode

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)

Programming Forums > Application Development > C++

Code is changing a variable that isn't involved