problem code isolated but makes no sense

JTR1080 · 2005-06-13T23:30:34

I have a complex problem in my tile engine that only occurs when i strictly use a loadMap function. For some reason when i read the tiles name from the text file into a string buffer on the third Node in the linked list it overwrites the second nodes stringHandle (ie bitmap3.bmp) with whatever is being read into it. So when it parses the list of surfaces it returns that second node which is not the correct surface, so every single tile painted is the second node (which is actually the first because the very first node is reserved as NULL anyway.) So it paints the first tile listed in the file for all the tiles. I've isolated the exact line this occurs so my question is why? here is the code: //load the map of file specified void map::loadMap(char* tileFile, videoMemory* memoryAlloc) { //debug buffer for breaking down file into components char tileBitmap[256]; char buffer[128] = {""}; long tileID; bool bWalkable; int xOfs, yOfs, zOfs; //debug printf ("next node string: %s", memoryAlloc->pFirst); //dont forget to create an origin (!!!INVALID COORDS BUT VALID RECT!!!) SDL_Surface* tileImage = memoryAlloc->querySurface("tile0.bmp"); this->pOrigin = new CgameTile(-1, -1, tileImage, -1, "tile0.bmp", false); ifstream mapStream (tileFile); if (! mapStream.is_open()) { cout << "Error opening file"; return; } //get header first!! first two lines are read as HEADER! mapStream.getline(buffer, 128); mapStream.getline(buffer, 128); while(!mapStream.eof()) { //break line down into components mapStream >> tileID; mapStream >> xOfs; mapStream >> yOfs; //node 2 of the link list handleString changes to //tileBitmap for unknown reason mapStream >> &tileBitmap[0]; //on this line mapStream >> zOfs; mapStream >> bWalkable; if(this->maxHeight<zOfs) { this->maxHeight=zOfs; } if(this->sizeOfMapX<xOfs) {this->sizeOfMapX=xOfs; } if(this->sizeOfMapY<yOfs) {this->sizeOfMapY=yOfs; } /*debug*/ //cout << tileID << "," << xOfs << "," << yOfs << "," << tileBitmap << "," << zOfs << endl; tileImage = memoryAlloc->querySurface(&tileBitmap[0]); /*read data feed it into the constructor */ CgameTile* newNode = new CgameTile(xOfs, yOfs, tileImage, zOfs, &tileBitmap[0], tileID, bWalkable); this->addTail(newNode); } return; } i've experienced this before somewhat, i would guess its some kind of memory going to a part of an array its not supposed to and overiting the handlestring (how i have no idea) but i already investigated tileBitmap by "watching" it and it goes to only the amount allocated and then terminates '\0' so it looks sound. so whats going on? thanks for any help

For Beginners

Started by JTR1080 June 09, 2005 11:44 AM

13 comments, last by Dave Hunt 18 years, 10 months ago

Lacutis

301

June 13, 2005 01:29 PM

Quote:Original post by JTR1080
Quote:Original post by Zahlman
C++ provides tools for dealing with this sort of thing in a way that's easy and *works*. In particular, it provides std::string (which also avoids problems with needing a particular buffer length).

I think that is my problem, the constructor for the surface with the overloaded
value of char* handleName, sets that char* to whatever the address in memory
handleName is, which is probably tileBitmap array so when it gets changed to
the new variable it changes the handleSurface. I'm changing the members of Csurfaces to have char intstead of char* to hold the data, the only problem is converting between the two so i have to write some annoying code like
*** Source Snippet Removed ***
hopefully it works

edit: problem solved! :)

No, the problem as was mentioned by Zahlman is that you are using char's and char *'s when you should be using std::string. There really isn't many reasons now adays when you actually want to use a char *. It really is in your best interest to learn how to use std::string. It's way easier to handle and can be converted to a char * if needed to by some archaic api function.

You are basically doing a lot of work to work around a problem that already has a valid answer. Please consider reading up on std::string.

Dave Hunt

4,872

June 13, 2005 02:03 PM

Quote:Original post by Lacutis
No, the problem as was mentioned by Zahlman is that you are using char's and char *'s when you should be using std::string.

No, the problem was exactly as stated - assigning the address of the source to the destination, rather than making a copy. The "best" solution may be to use std::string instead, but that isn't the "problem". It is perfectly possible to get his code working without std::string. Less clean, but not impossible.

CyberFox

198

June 13, 2005 03:38 PM

char* something = something_else;

This will make something a pointer to something_else. You want to copy the data instead. In windows the following code will work like a charm:

strcpy( something, something_else );

Alternatively you could write a function that loops through both strings and copies the data over, this however requires assembly language to be done at a speed comparable to strcpy.

** edit **
Don't let using c style strings scare you, click here instead. [cool]

- FoxWolfDesigns -

Zahlman

1,682

June 13, 2005 04:37 PM

Quote:Original post by Dave Hunt
Quote:Original post by Lacutis
No, the problem as was mentioned by Zahlman is that you are using char's and char *'s when you should be using std::string.

No, the problem was exactly as stated - assigning the address of the source to the destination, rather than making a copy. The "best" solution may be to use std::string instead, but that isn't the "problem". It is perfectly possible to get his code working without std::string. Less clean, but not impossible.

I've been doing maintenance work recently... please don't tell me that "un-clean" code isn't a "problem". :)

Dave Hunt

4,872

June 13, 2005 11:30 PM

Quote:Original post by Zahlman
I've been doing maintenance work recently... please don't tell me that "un-clean" code isn't a "problem". :)

I wouldn't dream of it. I've dealt with other people's (and my own) unclean code for 25 years.

Now that the OP's code is working, perhaps he has learned something about pointers. Hopefully he will take a look at std::string for future use. But, he needed a solution to an immediate problem, not a lecture on the virtues of the standard C++ library.

problem code isolated but makes no sense

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problem code isolated but makes no sense

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