I explained you point by point where the problem is and how it occurred. Despite of it, you repeat your ideas about pointers. It is rather ridiculous, because I have the source code, generated asm file and result of disassembling of exe file (which can be compared with the asm file, generated by compiler). Finally, I can (and I did) run my exe file under debugger. You have no such options at all. Under such circumstances it is very strange idea to try to explain me not what actually happened, but what might happen!

jschell wrote:

I read the following which you posted.
 
"but occurred again after some insignificant change in code (which was made far from the procedure, where problem occurred!)"
 
Presumably you do not understand what that statement means in terms of what I said and in terms of what you are claiming.

I do know. Assume you have a pointer, which points yo some array. Sentence like *(p+k)=a may cause a problem if k is greater than array's size. This is the typical problem, associated with pointers. In my case all was different. What I wrote clearly meant that I had changed the source C++ code, then compiler built executable and the problem disappeared. Then I changed code again, recompiled it and the problem occurred again. That's just what I meant. Where do you see pointers? Moreover, at that very moment when I wrote aforementioned text, I did not know, where the problem was. I only noticed, that code worked correctly when I had excluded max and min. But problem occurred again! The most remarkable was the fact that I did not change suspicious procedure- changes had made far from it. But if one single line of code has been changed, compiler compiles the whole file with this line of code. I got compiler to build release with debug info and ran procedure under debugger. This was how I found where the problem is- I noticed that very command, which overwrote RECT structure and immediately found, why it happened. That's all.

jschell wrote: Either you didn't read what I said in my previous replies or didn't understand what I said. I did. It was you who did not read (or did not understand what he read). Look at quotes from your messages: I want to emphasize again that the pointer bug could be anywhere. The behavior you are seing is a symptom not a cause. Don't know how to state this more clearly. Either you have a pointer bug or there is a compiler problem. If the latter then reducing the code will demonstrate it AND changing code far from it and unrelated will NOT impact it. Conversely if the former then you will not be able to reduce it because the code that you are looking at is not the source of the problem. You have a C++ application and do not use pointers ANYWHERE in the application? (Again is has NOTHING to do with pointers directly associated with the code where you think the bug is.) There are empty words about what might happens. Nothing common with real situation. Compiler placed temporary variable too close to another one and when the tv5476 was used, RECT structure was partially overwritten. So simple. It is no pointer's problem- the compiler's one.

I do not think where the bug is. I know it. I know exactly where variables was incorrectly allocated in stack and which command overwrote data. What are you talking about pointers? I do use them, of course, but they was not the cause. It is pointless to discuss here what might happens, ignoring all available info.

There was no pointer bugs at all. I declared no pointers, but the structure- RECT lrct. And some local variables too. Compiler allocated them in a stack and added some temporary variables. In a such way: _lrct$=-212; tv5476=-204; It is a time bomb, which might explode in any time. And it did. That's all. So simple.

Interesting bit about the size comments. I don't recall ever seeing that - maybe a different setting... Which compiler do you use? I only asked it to generate asm file with source code. All the rest was default settings (Sorry, later I added /Zi to generate debugger's symbols in release version. But it does not affect on generation of asm listing) I trust that by now you realized that it is hard for us to reproduce the exact situation that led to the problem. I do. You have no choice but to trust me (and stop looking where is light!). I still hold that it's dangerous to deduce anything from optimized code, short of print statements or similar right in the original code: you'll never know just what the compiler did, and why, to optimize your memory footprint and performance. It's difficult to draw correlations from assembler to the original code, and the expectations that come with it. But I do know exactly, what compiler does!!! What do you think asm listing exists for? Correlation is very simple and there are no problems with it. No matter, which sort of optimization is in use, resulting exe file must do the same things, and no matter, which optimization was used. The code you posted doesn't look very complex. About the only optimization I would anticipate is that some of the local variables would be stored in register only, rather than on the stack. But then, optimizers work in mysterious ways - you'll never know what kind of optimization they can come up with until you see the code... I saw. And without it I would never find, where the problem is. GOTOs are a bit like wire coat hangers: they tend to breed in the darkness, such that where there once were few, eventually there are many, and the program's architecture collapses beneath them. (Fran Poretto) Even Straustrup claims, that there are situation, when goto is useful. Assume you need get out of nested loops... do { do { do { if(something is wrong) goto Skip_loops; } while (cond A) } while(cond B) } while(cond C) Skip_loops:;

Stefan_Lang wrote: Therefore I decided to derive it based on you statements elsewhere: Variant B contains code that works by your own statement elsewhere. neither contains the max() funtion you refer to in your original question. So B is the working and A the not working - albeit not the original - version. Q. E. D. Again- I never claimed, which variant works and which does not. It was my question. And what "not the original version" means? I made my own investigation since the time, when I asked my first question. I changed code many times. I found, that no min nor max are not the source of the problem. There is no need in demonstrating of the rest of original code- it is the same for A and B. The difference is only here, in these few lines. And my question was- how could it be- both variants are correct. So you cannot answer to my question. Should I send you the answer or you will think for a while? As for what is pointless or not: advice is only pointless if it isn't heeded. You believe that the debugger shows you every information correctly? It doesn't. It can't. It's physically impossible. Why? Which part is hidden? Pipelines? Debugger demonstrates me all what I need to understand the core of situation. You must work really hard, if you want to cheat (or to trick- whichever word do you prefer) debugger. It happens mostly with self-modified code. I've dealt with optimizers 30 years ago: back then it wasn't to hard to anticipate what it would do, and in C you could often emulate pretty much the same without having to invoke the optimizer at all. meaning well optimized C code ran almost as well in debug mode as it did in release. I've dealt with optimizers 20 years ago, and it got more tricky. Still, well optimized C-code often turned out to be near optimal. I've dealt with optimizers 10 years ago, and the experience was very different: for one, the same optimizations in C code sometimes led to slower code, because it prevented the optimizer from performing extremely sophisticated optimizations that you'd never have thought of. Plus the size of the codebase made it impossible to optimize all of your code in that way anyway. At that point I stopped trying to optimize my C/C++ code by hand. More than strange idea. Hi-level optimization cannot be performed by compiler. Low-level usually yes, but not always. Nowadays, when I check release code that doesn't do the same as debug code, I often find that half the variables aren't on stack, and some others get overwritten at unex

Stefan_Lang wrote: 1.a) I realize that one is from the generated assembler code , but "I am able to see" is not an answer to my question. But never mind, you later wrote the original symbol is named _lrct, which I consider sufficient information at this point. Not exactly. In my code was a simple line like RECT lrct; compiler converted it into tv6649 = -332 ; size = 4 _lrct$ = -328 ; size = 16 _sf$204092 = -312 ; size = 8 There is no "sizeof"; yeah this operator made me problems once or twice. Look at how here lrct is placed- just correctly (it is another procedure! I rewrote that one, which caused problems, but as I wrote, there was difference not 16 bytes, but only 8. (I cannot show you the code, which caused problem- I rewrote it. Wrong allocation can be found now only here, in this tread) Considering the fact that symbols starting with '_' are common within windows system libaries and the MFC, and 'rct' is a common name fragment used for windows rectangle types and variables, I presume this is the Windows RECT struct[^] that you're talking about? Positive. But _ (and $ as well) was added by compiler. 1b) Are you saying you used the sizeof() function? That would be the only way I know of the compiler can 'tell' you as much. Or if you derived it from bits of the assembler code, I have to trust your word for it - I don't don't know how to extract that kind of information. I did not tell it- look up. Compiler wrote its size as a commentary in asm listing. 1c) it could have been different procedures, or even different threads. Before your more recent answers there was no way to tell. So this isn ot (part of) the cause of the problem. 2 As mentioned in another post: you can't trust debugger output in optimized code! Some variables may not be stored in the stack at all, others may be overwritten before they expire, and addresses used to view a particular element may not contain the correct value, or the most recent state of the variable, due to caching, or memory optimization. The only way to be sure of the actual, current state of a variable, is print it out to the console or maybe log file. What makes you think so? I watch at assembler code (well plus the source one), when I run release under debugger. And it demonstrates me just what it does. 4 I meant memory allocation, as in whether they are on the stack, the heap, or temporaries. But in light of the other responses this is no longer important. 5: see 2. - Don't trust the debugger in optimized code.

Stefan_Lang wrote: In the meantime I've spotted the code that you posted in a different branch of this thread. It isn't the original code though, and doesn't provide sufficient insight to answer any of the questions I posted. You state that variant A doesn't work, but it doesn't use the max() function, so we have to assume that the assembler code generated from that doesn't match the bits you later found to be incorrect (if they are indeed that - we still do not know) What do you mean, writing "it isn't the original code?" That I copied it from somewhere or what? I never stated, that variant A does not work. It is your idea. I asked, which works and which not (and why). You was not able to answer this question and preferred to ignore it. In the code you posted you use some variables that are only referenced over a couple of lines. They may not in fact be stored in the stack at all! As a result, the debugger will not show their contents in the optimized release code. Similarly, if you define a struct with data that is never referenced, the compiler may decide to optimize away the unneeded bits, reducing the size of the struct. You haven't posted the definition of the struct, nor where it's accessed, so it's impossible to tell if that is the case. All fields of the RECT structute was later used. If compiler decided that they are no more in use, it is just its bug. RECT structure is so well-known, that i did not placed its definition here. It contents 4 fields of type long- top, left, right and bottom. Just 16 bytes. I ran release version under debugger and I saw all assembler commands and order of their execution. Therefore, I know which variables was not stored in a stack and which temporary variables (which I did not declared!) was stored and where. I could go on and easily bring up half a dozen or more other optimization techniques that you appear to be unaware of, and that will confound your ability to read useful information from the debugger alone within optimized code. But it's pointless. Pointless is to repeat things like "there are more things on the Earth, on the heaven, than any dreamt of in our philosophy". What makes you think that I do not know about optimization? Stop walking around and answer to one simple question: why local variable, visible and accessible, was overwritten? You cannot name at least one more or less credible reason. If it is not visible, I couldn't get access to it and debugger wouldn't show it. Just this situation happens with variables, which are used in

Well, I've just answered, but I do not see it... Well, let's go point by point Stefan_Lang wrote: You should really look at the problem again and consider some or all of the following questions: 1. Where did you get the information that - _lrct$ refers to the start address of the RECT struct you're referring to What do you think .asm files exist for? Compiler made them and I was able to see, where local and temporary variables was allocated. - the RECT struct is really 16 bytes in size Nice question, it comes to my mind too- but the same compiler was so kind, that showed me the size of a RECT structure - the offsets you show are in fact relative to the same base address You should know, that ebp register remains constant within any procedure! And in this particular case all local and temporary variables was addressed via ebp. 2. Did you derive from your observation of these addresses that part of your data is overwritten, or did you check the actual RECT structure to verify that? I saw it, running my prog under debugger and I know which command (fst) overwrote aforementioned RECT (in fact, only right and bottom). 3. What are the original declarations of the C/C++ symbols corresponding to the two addresses _lrct$ and tv5476? RECT lrct; the second variable is local storage, using to temporary storage of ST(0) 4. How were the two objects allocated? I wrote it, but I can repeat it again. _lrct=-212 and tv5476=-204 (number a decimal ones!) It means, that command fst tv5476[ebp] overwrites 8 bytes- one half of lrct structure. 5. Are you sure that one of them (the RECT) hasn't been deallocated in the meantime? Note that optimizers may discard variables before the end of their lifetime as seen in code if they realize it is no longer used! It would be possible, but in such case debugger refuses to show such variable and gives message like "expression cannot be evaluated". Moreover, compiler wouldn't let me to use a variable outside of the block, where it was declared. I'm sure I could think of more questions, but this could be much more productive if we could see the actual code ... You saw it. Answer a question, originally addressed to Richard- which variant (and why) refuses to work properly.

Dear Stefan, it seems to me, that I have to remind you some theory. Local variables within some procedure may be addressed via ebp or esp. In my particular case they was addressed via ebp. It is much simpler to read such code, because ebp remains constant within a procedure. I some local variable is defined within some block, it becomes inaccessible, when eip leaves this particular block. Its place may be overwritten by something else, that's correct. But simultaneously debugger refuses to show this variable!!! But it showed it- therefore, lrct (16 byte RECT structure) was in its own block, was visible and accessible. But it was partially overwritten- 8 bytes was used as temporary storage for ST(0). That behavior cannot be taken as a normal one. And not lrct only- same fate waited h and maybe something else.

It is only my suggestion. There are few books on debugging, and this one is really useful.

Here you are. I could you recommend one useful book, written by John Robbins- "Debugging Applications". If you haven't read it, you'll find there many useful things.

I can only recommend to you reread the whole discussion. I do know now, where the problem is. OK, compiler is absolutely stable. No problem with it. But it works incorrectly. It reserves some places in a stack for temporary variables. In fact, these variables stores content of co-processor's registers. Some of such temporary variables overlap (partially or completely) another local variables. It might be no problem- some local variables are visible only within some block, not within the whole procedure. If execution of code leaves some block (part of code within such {} brackets), all variables, declared within this block, becomes inaccessible and their place in a stack may be rewritten by another local variable. But compiler creates exe file, which performs this op even when some local variable is visible and accessible!!! And it happens not only with RECT structure, but with some of other local variables too. I saw this process, when I was running release version under debugger. Look up, where I placed piece of my code. Variable "h" was rewritten at least once. If it is not a compiler's bug, I'm definitely an elefant.

You cannot help me. How could you help me, if you even do not know, which bytes overwrites fst command? I do not send my procedure only because of its size. And I know now, where the problem is. Well, if you think that the problem is in my code, look at two small pieces and try to understand, why and which one works properly, but the other does not. I fixed the problem (well, not completely- I only rewrote my code, using my knowledge about compiler's incorrect behavior. lrct was removed at all.) Variant A: int xmin=xf+(fct*pdpr->m_croprect[Right].left-xf-ddi)*(xl-xf)/(yr1-yr0); int xmax=xl+(fct*pdpr->m_croprect[Left].right-xl)*(xl-xf)/(yl1-yl0); h=0.5*pdpr->m_croprect[Left].top+0.5*pdpr->m_croprect[Left].bottom; pdpr->GetKorrHorz2D(xfirst, xlast, Dv, Dh, h, ddi, yh, yv, yhs, yvs, pKorr, ph, pv); pdpr->GetCorrLineH2(xfirst, xlast, h, ddi, yh, yv, yh, yv, ph, pv, 0, 0); yl0=xf+0.5*yh[xf]; yl1=xl+0.5*yh[xl]; yr0=xf+ddi-0.5*yh[xf]; yr1=xl+ddi-0.5*yh[xl]; int xl2=xf+(fct*pdpr->m_croprect[Right].left-xf-ddi)*(xl-xf)/(yr1-yr0); if(xl2>xmin) xmin=xl2; int xr2=xl+(fct*pdpr->m_croprect[Left].right-xl)*(xl-xf)/(yl1-yl0); if(xmax>xr2) xmax=xr2; h=0.1*pdpr->m_croprect[Left].top+0.9*pdpr->m_croprect[Left].bottom; pdpr->GetKorrHorz2D(xfirst, xlast, Dv, Dh, h, ddi, yh, yv, yhs, yvs, pKorr, ph, pv); pdpr->GetCorrLineH2(xfirst, xlast, h, ddi, yh, yv, yh, yv, ph, pv, 0, 0); yl0=xf+0.5*yh[xf]; yl1=xl+0.5*yh[xl]; yr0=xf+ddi-0.5*yh[xf]; yr1=xl+ddi-0.5*yh[xl]; int xl3=xf+(fct*pdpr->m_croprect[Right].left-xf-ddi)*(xl-xf)/(yr1-yr0); if(xl3>xmin) xmin=xl3; int xr3=xl+(fct*pdpr->m_croprect[Left].right-xl)*(xl-xf)/(yl1-yl0); if(xmax>xr3) xmax=xr3; xfirst=xmin+0.02*(xmax-xmin); xlast=xmax-0.02*(xmax-xmin); Variant B: int xl1=xf+(fct*pdpr->m_croprect[Right].left-xf-ddi)*(xl-xf)/(yr1-yr0); int xr1=xl+(fct*pdpr->m_croprect[Left].right-xl)*(xl-xf)/(yl1-yl0); h=0.5*pdpr->m_croprect[Left].top+0.5*pdpr->m_croprect[Left].bottom; pdpr->GetKorrHorz2D(xfirst, xlast, Dv, Dh, h, ddi, yh, yv, yhs, yvs, pKorr, ph, pv); pdpr->GetCorrLineH2(xfirst, xlast, h, ddi, yh, yv, yh, yv, ph, pv, 0, 0); yl0=xf+0.5*yh[xf]; yl1=xl+0.5*yh[xl]; yr0=xf+ddi-0.5*yh[xf]; yr1=xl+ddi-0.5*yh[xl]; int xl2=xf+(fct*pdpr->m_croprect[Right].left-xf-ddi)*(xl-xf)/(yr1-yr0); int xr2=xl+(fct*pdpr->m_croprect[Left].right-xl)*(xl-xf)/(yl1-yl0); h=0.1*pdpr->m_croprect[Left].top+0.9*pdpr->m_croprect[Left].bottom; pdpr->GetKorrHorz2D(xfirst, xlast, D

I will. I've just registered at M$'s site. And I got you all info to understand, where the problem is. For me situation is clear. What I got, running release under debugger: lrct {top=30 bottom=958 left=162 right=750} 0041A88F fst qword ptr [ebp-0D4h] lrct {top=30 bottom=1080213504 left=162 right=0} Here you may see, what made one single command- RECT structure before and after this command. What additional info do you need? Prefix "tv" definitely means Temporarily Variables. This variable was placed too close to storage of RECT structure and fst overwrote it. If you cannot see it, I wash my hands. If you do not know, which bytes fst overwrite, sorry, man- there are problems, which obviously cannot be solved at the level of source code. One must dig deeper. And to do it, you must know many things, like assembler, structure of stack frame and so on and so on. (lrct was stored at ebp-0DCh)

There is no way to demonstrate problem, if compiler is unstable. problem disappeared, when I replaced max() and min(), but occurred again after some insignificant change in code (which was made far from the procedure, where problem occurred!). I used default compiler's options. Later, when I was looking for the source of the problem, I created database and set /Zi switch for the release version. After these actions I was able to find the very command, which destroyed my data. The next was trivial- I find offsets of local variables and noticed, that some of them was incorrectly placed (one partially overlaps another). This is the bug in compiler, not mine.

I clearly demonstrated, what cased problem in particular. I can repeat it again. There was two local variables: _lrct$ = -212 ; size = 16 tv5476 = -204 ; size = 8 The next command rewrites 8 bytes of _lrct$ fst QWORD PTR tv5476[ebp] That's all info. Which data in particular was replaced and by what- means nothing. The only important fact is that data was replaced with something else.

I did it. Problem was caused by incorrect allocation of local variables in stack frame. This is what I hardly can change- it is a bug in compiler. The only important fact is that one value was replaced by another. Exact values of variables here mean nothing.

I need help. Question is, if any of you can give me some more or less valuable tip. When I asked my question the first time, I was not sure, that a bug really presents in Visual Studio. Now I know it. Problem is, what I have to do in such sorrowful situation. If someone else met such problem and fixed it, such person could share his experience. May be, this bug presents only in my own exemplar of Visual Studio- may be, it was damaged in some way and produces code with defects- in such case re-installation will solve this problem. Or such bug presents in each exemplar of Visual Studio 2005- in such case, I have to throw it away and buy 2008 or 2010. I know about a bug in Borland's compiler.