I am trying to find an error in my code. The problem is the error occurs in a loop. But the loop iterates about 500 times. Instead of clicking through the loop. Is it possible to skip over a certain amount of the loop ??
VS allows you to set a condition on a breakpoint in terms of variables that are in scope. So, in your case, you can test against the loop counter.
Here is a crude answer:
if ((iter % 10) == 0) {
int stop = 1;
}
Then place a break-point at "int stop = 1;". Perhaps, there is a better way in VS but this is what I do from time-to-time.
You can assign new values to variables during debug session. Step through the loop statements as many times as you like, then set your loop counter (or whatever other vars maintain loop condition) to terminate the loop.
Just put the breakpoint in the loop like indicated below >>. Use F5 to get to the condition that causes failure so you can loop through the individual pass. How to know where to break is up to you.
for (int i = 0; i < LOOPMAX; i++) {
>>some_proc(i);
some_other_proc(i);
some_third_proc(i);
}
By pressing F5 it'll continue running till it gets to the next breakpoint (the next pass through the code). Sure you'll have to hit it 500 times, but that beats some thousands of times. Combine this with #Troubador code above.
PS: This answer IS really simple, but some people don't know they can do this.
Related
I'm trying to make a limit for a program where if you keep answering the wrong question the program shuts down. How do I do this? I've tried adding a limit to a loop where once the limit ends if the loop exceeds the limit then I should end. I've also tried to turn the error message into a string variable and counting and adding a limit to how many times it can be printed. How do I fix this? Here's the code:
std::cout << error; // error is the error message
cin.clear();
cin.ignore(123, '\n');
std::cin >> units;
One simple solution could be a while loop with a counter;
int tries = 3;
while (tries--) {
// Other code
}
This will run the "other code" until tries reaches 0, and tries is decremented each time you go round the loop.
I would advice using a counter. Whenever the user inputs a wrong answer the counter should increase. As long as the counter would be smaller than your limit of choice user input can continue. When:counter == someLimit, you can provide some output to let the user know he rached the limit and stop the execution.
Unfortunately a program I wrote in C++ has a bug (or bugs), yet I can't deduce what it is since only a single output line doesn't match the expected output (the input file has 3K lines of input). I know which input line is the problematic, yet it's over 2K lines into the input file so debugging it manually isn't very efficient.
Is there any way to let the debugger run "alone" with the first 2K lines and stop exactly before trying to execute the problematic input line? I use Windows and eclipse but don't mind switching the IDE or switch to Linux if necessary.
Thanks in advance!
Don't reinvent the wheel!
Eclipse has powerfull feature Enable condition for breakpoint.
Set breakpoint in your code
Right-click on breakpoint - "Breakpoint properties"
Check "Conditional"
Write your condition when breakpoint should be stopped (you have access to scope and global variables)
Here is Eclipse help page. Breakpoint Enable Condition
(with screenshot)
Well, eclipse may well have advanced debugging features, and to tell the truth I do not know the first thing about eclipse, but FWIW you can easily simulate what you want.
What you have is:
for(i = 0; i < lineCount; ++i)
process one line
Add a condition to check the line number and place a breakpoint inside it!:
for(i = 0; i < lineCount; ++i)
if(i == 2000)
{
int x = i*i; //random line, just add your breakpoint here!
}
process one line
Since you know exactly what line is problematic, just a dummy if statement which would check the contents of the line, and if mathces your problem line, do nothing - and put a breakoint at this line.
I am using gdb-7.0.1 and I think I have detected a bug in a certain section of my code, which
has a for loop. The for loop looks like
for (int i=0 ; i< end ; ++i )
{
//Code here.
}
Here end is a very large integer. The code does not crash at the first iteration, and seems to crash somewhere at iteration number end/2.
Since I want to understand the behaviour of the code at iteration number end/2 , just stepping and nexting from i=0 till I reach this iteration point, is unfeasible.
Is there a way to tell gdb to continue through a for loop till i gets the value end/2 and then wait for the user to manually step through iteration number end/2?
I am using gcc-4.5.2 on Ubuntu Linux
Here's a tutorial on conditional breakpoints with gdb.
I'm guessing you didn't know the term for this, otherwise it would have been easy to google.
When you set the breakpoint it'll give you a breakpoint number (for the moment, let's assume it's 1). You'll then make that breakpoint conditional, something like:
condition 1 i==end/2
You have to use conditional breakpoint. Here is more about it: http://www.cs.cmu.edu/~gilpin/tutorial/#3.4
And on SO: How do I set a conditional breakpoint in gdb, when char* x points to a string whose value equals "hello"?
In your case (not tested):
break <line_number> if i==end/2
You should be able to place an if (i == (end/2 -1)) { Foo; } in there then set a breakpoint at Foo, which would allow you to continue stepping from there.
If end is big (in the tens of thousands), then the conditional breakpoint solution can be very slow - gdb has to evaluate the condition each time round the loop. If this is a problem for you, then you can use this trick:
for (int i=0 ; i< end ; ++i )
{
if (i == end/2)
i %= end ; // This has no effect, but lets you set a breakpoint here
//Code here.
}
I do this all the time :-)
Another solution is to set a skip-count on the breakpoint. I use gdb in a Qt environment, so I can't give you the gdb syntax. But it's faster than setting a condition.
I have a function that creates and insert some numbers in a vector.
if(Enemy2.dEnemy==true)
{
pt.y=4;
pt.x=90;
pt2.y=4;
pt2.x=125;
for(int i=0; i<6; i++)
{
Enemy2.vS1Enemy.push_back(pt);
Enemy2.vS2Enemy.push_back(pt2);
y-=70;
pt.y=y;
pt2.y=y;
}
Enemy2.dEnemy=false;
Enemy3.cEnemy=0;
}
It should insert 6 numbers in two vectors, the only problem is that it doesn't - it actually inserts more.
I don't think the snippet will run unless Enemy2.dEnemy == true, and it won't stay true for ever.
The first time the snippet runs, then Enemy2.dEnemy is set to false and it shouldn't run again.
I don't set Enemy2.dEnemy to true anywhere except when the window is created.
If I insert a break point any where in the snippet, the program will work fine - it will insert ONLY 6 numbers in the two vectors.
Any ideas what's wrong here?
ok so i did some debugging.
i found that Enemy2.dEnemy=false; is being skipped for some reason.
i tried to do this to see if it was.
if(Enemy2.dEnemy)
{
pt.y=4;
pt.x=90;
pt2.y=4;
pt2.x=125;
for(int i=0; i<6; i++)
{
Enemy2.vS1Enemy.push_back(pt);
Enemy2.vS2Enemy.push_back(pt2);
y-=70;
pt.y=y;
pt2.y=y;
}
TCHAR s[244];
Enemy2.dEnemy=false;
if(Enemy2.dEnemy)
{
MessageBox(hWnd, _T("0"), _T(""), MB_OK);
}
else
{
MessageBox(hWnd, _T("1"), _T(""), MB_OK);
}
Enemy3.cEnemy=0;
}
well the message box popped saying 1 and my code worked fine. it seems that Enemy2.dEnemy=false; doesn't have time to run ;/
blahblahblahblahblahblahblahblahblahblahblahblahblahblahblahblah!
ok i found where is the real problem which was causing to insert more than 6 numbers..
it was where i was asigning Enemy2.dEnemy=true;
if(Enemy2.e1)
{
Enemy2.now=time(NULL);
Enemy2.tEnemy=Enemy2.now+4;
Enemy2.e1=false;
}
if(Enemy2.tEnemy==time(NULL))
{
check=1;
Enemy2.aEnemy=0;
Enemy2.dEnemy=true;
}
the problem seems that the second if runs more than one time, which is weird!
First things first: get rid of that abominable if (Enemy2.dEnemy == true) - it should be:
if (Enemy2.dEnemy)
(I also prefer to name my booleans as a readable sentence segments like Enemy2.isABerserker or Enemy3.hasHadLeftLegCutOffThreeInchesBelowTheKnee but that's just personal preference).
Other than that, the only thing I can suggest is a threading problem. There's nothing wrong with that code per se, but there is a window in which two threads could enter the if statement and both start pushing values into your vector.
In other words, if thread 1 is doing the pushing when thread 2 encounters the if statement, thread 2 will also start pushing values, since thread 1 has yet to set dEnemy to true. And don't think you can just move the assignment to the top of the if block - that will reduce but not remove the window.
My advice is to print out the contents of the vectors in the situation where they have more than six entries and that may give a clue as to what's happened (post the output here if you wish).
Re your update that the second if below is running twice:
if(Enemy2.e1)
{
Enemy2.now=time(NULL);
Enemy2.tEnemy=Enemy2.now+4;
Enemy2.e1=false;
}
if(Enemy2.tEnemy==time(NULL))
{
check=1;
Enemy2.aEnemy=0;
Enemy2.dEnemy=true;
}
If this code is executed twice in the same second (and that's not beyond the bounds of possibility), the second if statement will run twice.
That's because time(NULL) give you the number of seconds since the epoch so, until that second is over, you may well be executing the contents of that if thousands of times (or more).
If this problem disappears when you put in a breakpoint or a diagnostic output message, that's a strong clue that the problem is undefined behavior, which is usually caused by something like dereferencing an uninitialized pointer or careless use of const_cast.
The cause of the problem probably has nothing to do with the code you're looking at. It's caused somewhere else and just happens to show up here. It's like someone being hit by a falling brick: the obvious symptom is a man lying unconscious on the sidewalk, but the real problem has nothing to do with the man or the sidewalk, it's several stories up.
If you want to find the cause of the error, remove your diagnostics until the problem reappears, then start removing everything else. Prune away all of the other code. Whenever the error stops, back up until it starts again; if you don't see the cause of the error, start pruning somewhere else. Eventually the bug will have nowhere to hide.
I'm trying to debug a method which among other things, adds items to a list which is local to the method.
However, every so often the list size gets set to zero "midstream". I would like to set the debugger to break when the list size becomes zero, but I don't know how to, and would appreciate any pointers on how to do this.
Thanks.
Why not use conditional breakpoints?
http://blogs.msdn.com/saraford/archive/2008/06/17/did-you-know-you-can-set-conditional-breakpoints-239.aspx
in C#
if(theList.Count == 0){
//do something meaningless here .e.g.
int i = 1; // << set your breakpoint here
}
in VB.NET
If theList.Count = 0 Then
'do something meaningless here .e.g.
Dim i = 1; ' << set your breakpoint here
End If
For completeness sake, here's the C++ version:
if(theList->Count == 0){
//do something meaningless here .e.g.
int i = 1; // << set your breakpoint here
}
I can give a partial answer for Visual Studio 2005. If you open the "Breakpoints" window (Alt + F9) you get a list of breakpoints. Right-click on the breakpoint you want, and choose "Condition." Then put in the condition you want.
You have already got both major options suggested:
1. Conditional breakpoints
2. Code to check for the wrong value, and with a breakpoint if so happens
The first option is the easiest and best, but on large loops it is unfortunately really slow! If you loop 100's of thousands iterations the only real option is #2. In option #1 the cpu break into the debugger on each iteration, then it evaluates the condition and if the condition for breaking is false it just continiues execution of the program. This is slow when it happens thousands of times, it is actually slow if you loop just 1000 times (depending on hardware of course)
As I suspect you really want an "global" breakpoint condition that should break the program if a certain condition is met (array size == 0), unfortunately that does not exist to my knowledge. I have made a debugging function that checks the condition, and if it is true it does something meaningless that I have a breakpoint set to (i.e. option 2), then I call that function frequently where I suspect the original fails. When the system breaks you can use the call stack to identify the faulty location.