Weird Ouput

This is a discussion on Weird Ouput within the C++ Programming forums, part of the General Programming Boards category; Okay. I'm currently designing a small little "maze" game. Heading towards an ascii dungeon game, but keeping it simple for ...

  1. #1
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    Weird Ouput

    Okay. I'm currently designing a small little "maze" game. Heading towards an ascii dungeon game, but keeping it simple for now. Simply, the program so far is meant to read in a text file containing the maze, copy to a terrain class which draws it to the screen class. The screen class then outputs the map. It reads it all in okay, but every time I output, the first line is all messed up. For example, a text file that contained:
    Here is some text.
    Here is some more.
    And here's a line.
    Outputs:
    O?¶a♦ is some more.
    And here's a line.
    I'm using notepad2 to edit the text and Cygwin to compile. I have tried both windows and unix format. I have tried all the different encodings. Has anyone else come across this? There's quite a bit of code so I won't post it until you ask for it. (Just in case it's not a programming issue.)

    Thanks.

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    I'd say the most likely culprit is that you're going past the end of some other data that in turn clobbers your string data. Try adding some debug prints to verify your string data at various places in the code, and narrow down the scope until you have one function (or a few lines), then analyze that bit of code.

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    Quote Originally Posted by matsp View Post
    I'd say the most likely culprit is that you're going past the end of some other data that in turn clobbers your string data. Try adding some debug prints to verify your string data at various places in the code, and narrow down the scope until you have one function (or a few lines), then analyze that bit of code.

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    I was able to add debugging code to verify that the file is being read correctly. I tried adding a sort of std::cout << charBeingProcessed << std::endl; kind ok stuff. Nothing was output.

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    So, you are saying that the strings are read OK, but later on they are not OK, which is exactly the point I was trying to make - some other bit of code is overwriting your string.

    Alternatively, you are not storing the text correctly -keeping a pointer to a string on the stack of a function that is no longer active is a classic example of this - been done by almost every programmer ever to write string handling code, I would expect.

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    Well, the function which draws the terrain onto the screen takes a pointer to the screen class. I removed the pointer, and the output is different but still messed up. The problem is that I can think of heaps of places where this map data is being transfered and copied. I'm just having a hard time figuring out where it's wrong.

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    Whenever you copy or otherwise process the data, add a printout to make sure it's OK. That's the best way to debug this sort of problem - or in a debugger, put a break on every function that processes the data and then check it at the end of the function - but that can be tedious if there's a lot of functions and a lot of data.

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    I have tried to output data in some of the copying processes. It's not actually outputing anything.

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    Quote Originally Posted by addle_brains View Post
    I have tried to output data in some of the copying processes. It's not actually outputing anything.
    Then your output isn't working right, so try fixing that first... ;-)

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    I may have figured it out. Is there a way to reset the "read position" in a file so to the start?

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    In C- style file handling (fopen, fread, fgets, and friends): fseek(stream, pos, SEEK_SET)
    In C++ style file handling (fstream class): seekg(pos) member function.

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    Ok. I managed to narrow it down where it's happening to a constructor:

    Code:
    #include <fstream>
    #include <string>
    #include <vector>
    #include <iostream>
    #include "terrain.h"
    
    
    using namespace Game;
    
    terrain::terrain (std::string fileName) {
    	
    	std::ifstream in(fileName.c_str());
    	
    	if (!in) {
    	
    		throw GameException("Cannot open terrain file.");
    	}
    	
    	else {
    	
    		std::string entry;
    		std::string longFile;
    		std::vector<string> stringVect;
    		
    		while (getline(in, entry)) {
    			
    			if (entry > longFile) {
    				longFile = entry;
    			}
    			
    			stringVect.push_back(entry);
    		}
    		
    		width = longFile.size();
    		height = stringVect.size();
    	}
    	
    	in.seekg (0);
    	terrainArray = new Array2D<char>(width, height);
    
    	char passTo;
    	while (in.get(passTo)) {
    		
    		for(
    			unsigned y = 0;
    			y < height;
    			y++
    		) {
    			for(
    				unsigned x = 0;
    				x < width;
    				x++
    			) {
    				terrainArray->Put(x, y, passTo);
    				
    			}
    		}
    	}
    	in.close();
    }
    The Array2D template was supplied by a lecturer, so it works. I've asked him about this issue, but all he said was to check my file format.
    Last edited by addle_brains; 08-18-2007 at 10:43 AM.

  12. #12
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    Code:
    			if (entry > longFile) {
    				longFile = entry;
    			}
    You are using "longFile" to determine the max size of the array, but you are comparing strings in alphabetica order, so, rather than comparing the length of the strings. So a shorter string will overwrite a longer one with alphabetically higher value, e.g. "Aardvark" < "Elk"

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    Okay, i've changed that to
    Code:
    if (entry.size() > longFile.size()) {
    	longFile = entry;
    }
    Regardless, that didn't fix the problem.

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    Don't know for sure, but I think you may want to add one to the size to allow for the string "abc" being 'a', 'b', 'c', '\0' : 4 chars.

    And watch for newlines that may not be taken in the "getline", but are taken in "in.get" perhaps?

    I don't know what else may be the problem.

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    >> while (in.get(passTo))
    That code should never run. The previous loop with getline goes until the stream reaches a fail state (which will happen after you pass the end of the file). You never clear the fail state, so get won't get anything and that loop will never be entered. Call in.clear() before that loop.

    Then, once you actually get into the loop, you do have to account for the fact that getline discards newlines but get reads them in.

    >> I think you may want to add one to the size to allow for the string "abc" being 'a', 'b', 'c', '\0' : 4 chars.
    There is no null terminator in C++ strings, its not relevant (technically there might be one in a given implementation, but again, it is not relevant).

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