One of my functions returns a 'msg' object... which is merely a string.
I got into 2 for loops in the function.
msg=''
for e in example:
msg+= "some crap"
msg+= "some crap1"
for sl in somelist
msg+= v.somevalue
msg+="-------------"
return httpresponse(msg)
There's an example of the code.
'somelist' contains two values... when the 'msg' returns it only returns the second of the two values! I'm rather confused.
Your code uses sl as the loop variable, then pulls values from v. I'm not sure how they relate. If the final message includes a number of copies of the last value, then probably you forgot to relate sl and v somehow. If it includes only a single copy of the last value, then perhaps the line of code appending to msg is actually outside the loop. This would mean nothing is appended as the loop progresses, then once it exits, the last value is appended.
If your code is exactly like that, it should work just like you want it to. However, as this clearly isn't the actual code, I'd guess you have msg = ... somewhere, when you should have msg += ... At least that's the most likely reason for the behaviour you're seeing.
If you have trouble finding where it goes wrong, put in there some "print msg" statements and test it by running your Django project in development server. You'll see where it goes wrong.
Related
Hello I have been having trouble with my program I've created a list and I have the following program
Its goal is to Read the 5 variables inside the text file 5 variables in 5 different inputs
so I manage to correctly show the list inside the while loop since every time a line is read it's printed untill .eof(End Of File)
My goal is that I am trying to print the list OUTSIDE of the while Loop that has already read and printed those 5 variables 10x the problem is that it repeats the last entered 5 Variables in the list
I and repeats that 10x (size of the list)
I've also tried something like this inside the for loop which I found in here:
int ID=it->ID;
string NAME=it->NAME;
int SEMESTER=it->SEMESTER;
string DIRECTION=it->DIRECTION;
double GRADE=it->GRADE;
As if those are nodes but I am a starter with nodes as well as lists and it seems to have failed
When I look at the code you've provided, I see that in your for loop the a_student is used, which is not updated by/with the iterator. Basically you're not looping over the created student list.
Maybe try using std::for_each (cppreference) it will save you a lot of time:)
Godbolt example: https://godbolt.org/z/fQUhcr
The issue on the left column of code is that you are not de-referencing the iterator. You never set the a_students variable inside the loop, so why do you expect it to change on each iteration?
Write something like:
a_students = *it;
inside the loop. However there is a simpler way. Instead of manually handling the iterators, use:
for (auto a_students: s_stl_list)
{
// do something with each "a_students" which will be AUTOmatically the right type
}
I am working with dirEntries. Great function by the way. I wanted to test for the number of files before I used a foreach on it. I looked here on stack overflow and the suggested method was to use the walkLength function (Count files in directory with Dlang). I took that suggestion. The return from it was a non-zero value - great. However, the foreach will not iterate over the result of dirEntries. It acts like the walkLength has left the dirEntries at the end of the range. Is there a way to reset it so I can start at the beginning of the dirEntries list? Here is some example code:
auto dFiles = dirEntries("",filter, SpanMode.shallow);
if (walkLength(dFiles) > 0)
{
writeln("Passed walkLength function");
foreach (src; dFiles)
{
writeln("Inside foreach");
}
}
The output shows it gets past the walkLength function, but never gets inside the foreach iterator.
Am I using dirEntries wrong? I have looked at Ali Cehreli's great book Programming in D as someone suggest. Nothing stuck out at me. I have looked online and nothing points to my interpretation of the problem. Of course, I could be completely off base on what the problem really is.
dirEntries gives you a range. You consume that range with walkLength and reach its end. Then you attempt to read more entries from it with the foreach loop. However, you have already reached its end, so there is nothing more to read.
You can either repeat the dirEntries call, use the array function from std.array to convert the range to an array, or use the .save function to create a copy of the range that you pass to walkLength.
If you don't care about the length and only care about whether it's empty, you can use the .empty property of the range instead of walkLength.
I have noticed on several occasions that I may be creating a problem (described below) when I lay my C++ code out as below. While it may not be ideal, I do it to save space sometimes.
I can only show you a small code snipped because the program is quiet large. Hopefully can articulate the problem clearly.
string st= "TestString,"; // I declare a string.
//further down in my code I want to remove the comma as I do below.
// I do it in the below syntax to save space. Ok, maybe not ideal but I did it.
if(st[st.length()-1]==','){st=st.substr(0,st.length()-1);}
cout << "My new string is: " << st << endl;
// I place a line of codeimmediately below my if statement.
The problem is, sometimes the code directly below my one line If Statement follows the logic of the If Statement when I thought that would be reserved for the code only int the { } .
It doesn't always happen but it does happen randomly. When I leave a space between the One Line If Statement and the code below it, the problem goes away.
Is there a common problem I have created here or is this just an unusual anomaly?
So I have this simple code snippet:
CString str;
..................
if ( str.IsEmpty() )
str = spRelease->GetID();
I want to put a conditional breakpoint on the last line to test if str is empty.
I tried this first:
str == ""
But I get this:
Error overloaded operator not found
Then this:
str.isEmpty() == 0
And get this:
Symbol isEMpty() not found
Any idee how this could be done ? Any workaround ?
Thanks.
Why don't you just put a normal breakpoint on the last line? You already know str is empty. If you want to double check whether your string is empty, I would use an ASSERT instead.
If you really have to check your string, you have to check m_pszData in your CString, so your condition looks like this:
str.m_pszData[0] == '\0'
In Visual Studio 6 you have the operation IsEmpty(), note that the first 'I' is uppercase. You also have the Compare() operation. Which version of VS are you using?
One pattern that I've seen for things like this is to add a bit of code like this:
if (some_condition) {
int breakpoint=rand();
}
This generates a warning about breakpoint being initialized but not used so it is easy to remember to take it back out. This also allows you test any condition you want, including invoking functions or anything else, without having to worry about restructions of the debugger. This also avoids the limit on the number of conditional breakpoints you can have that some debuggers have.
The obvious downsides are that you can't add one during a debug session, recompiling, remembering to take them out, etc.
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.