int a=0;
while (a<2)
{
//infos.stops is point to one array, called abc[10]
output = output + QString::fromStdString(*infos.stops)+ "." ;
infos.stops++;
a++;
}
ui->showMsg->setText(output);
The problem is infos.stops did show, but some funny characters appear like:
I have uploaded all my source code which is designed in QT Designer
http://uploading.com/files/eaddfaf8/bus.zip/
The problem line is at manager.cpp line 133.
Try using
output = output + QString::fromStdString(*(infos.stops))+ "." ;
I think i solved it after a bit testing your application. The following code segment should do it:
output = output+ "Stops travelled: ";
for(int a = 0; a < infos._numstops; ++a)
{
if(a)
output += ", ";
output = output + QString::fromStdString(infos.stops[a]);
}
output = output + "<br>";
Note that you have the member infos._numstops availlable and should use it. The if(a) is a nice trick if you want to output a comma separated list.
(I ran your application and noticed that the info struct does not include the stop where you're starting your path but the one where it ends. You should include the starting stop in the output or exclude the target stop. Further note that the += operator like in the if-body is a common way to append strings.)
In manager.cpp:103 you are calling DE1.cost(X,Y). This method creates a std::string array (passed) on the stack (datzz.cpp:432) and at datzz.cpp:502 you do
c.stops = passed;
which stores a pointer to a memory block allocated on the stack in the stops variable of your DatzEzy::info instance c. When the method cost(string, string) returns, the memory allocated for passed is freed and your output will be garbage. Never store pointers to stack allocated objects.
By the way, you should consider using const references when passing (read-only) strings in function calls, which avoids expensive copying.
Related
For the sake of me better understanding C++ strings, array and pointers; I want to know: Why is it that I can use a condition whereby I check if the index has reached the null-terminating character like this...
const char* myString = "Grandopolous";
for (int i = 0;;i++)
{
if (!myString[i])
break;
else
cout << myString[i];
}
So that works just fine. Here I am instead checking to see if the character equals something other than the null-terminating character and so I expect that if it doesn't the result should be not 0 and the condition should be true. but this does not work, and I simply cannot fathom why:
const char* myString = "Grandopolous";
for (int i = 0;;i++)
{
if (myString[i])
cout << myString[i];
}
This does not work on my machine and crashes, also it outputs a lot of unreadable error messages mixed with strange symbols. I don't think that part matters although it is the first time error have been printed to my console application instead of the debug console.
The reason I mentioned pointers is because I managed to get the condition to work using pointers instead of the array index syntax which I find much easier to read.
So could someone please help me understand why my first bit of code is valid and why my second is not.
It does work. The check for null isn't the problem.
Your program crashes because you got rid of the break so your program overruns the array then continues forever into the abyss.
Your debugger would surely have revealed this to you as you stepped through the program, observing i.
To reverse the logic of your first example, write:
const char* myString = "Grandopolous";
for (int i = 0;;i++)
{
if (myString[i])
cout << myString[i];
else
break;
}
I am working on city generation for a pcg game of mine. I have a for loop which makes 3 cities in random locations, I assign parentIteration to get that "id" for the city and do the same in the for loop where I make a building
for (int i = 0; i < 3; i++)
{
parentIteration = i;
std::srand(i);
_rootNode = GameManager::getSingletonPtr()->getSceneManager()->getRootSceneNode();
_cityNode = _rootNode->createChildSceneNode("cityNode " + parentIteration);
generateCity(std::rand() % 10000 + 10, std::rand() % 10000 + 10, std::rand() % 11 +1);
}
building
for (int i = 0; i < _numberOfBuildings; i++)
{
childIteration = i;
printf(" parent %d and child %d \n", parentIteration, childIteration);
Ogre::SceneNode* buildingNode = _cityNode->createChildSceneNode("citybuildingNode"+childIteration+parentIteration );
}
However when I try to launch the game it will crash on creating the second city. Saying it already has a name similar to what it is trying to write. Yet my printf clearly show that the numbers at that point are all unique. Anyone know how to resolve this issue? (added picture for proof of output)
The "itybuildingNode" in the error message suggests that
"citybuildingNode"+childIteration+parentIteration
is not working quite the way you wanted.
This is because of a couple things working against you:
"citybuildingNode" is a String Literal, and not a string object. It is litteraly just a bunch of characters in a row terminated by a null character and represented as a const char *, a pointer to that array of characters. It is low-level voodoo, the sort of stuff you might make a string class around. For more information see String Literals
Because it's not a string object, you can't pull any of the usual string object tricks like concatenating with a + and comparing with ==. But because it is a pointer, the compiler interprets + as an attempt to perform pointer arithmetic and reference another location in the array. It compiles, but note how it turned "citybuildingNode" into "itybuildingNode". Oops.
What this looks like is something like:
const char* temp = "citybuildingNode"
_cityNode->createChildSceneNode(temp + childIteration + parentIteration);
which resolves to
const char* temp = "citybuildingNode"
_cityNode->createChildSceneNode(&temp[childIteration + parentIteration]);
Even if it was a string object, the C++ standard string object, std::string does not allow you to add numbers to strings. It only adds strings together to build a bigger string. To add a number to a std::string, you have to turn the number into a std::string. std::to_string can help you here, but there is a cleaner-looking way to do this with std::stringstream
Eg:
std::stringstream nodename("citybuildingNode");
// builds a string stream around the string literal
nodename << childIteration << parentIteration;
// writes the numbers into the stream the same way `cin << number;` would
// turning the number into a string for you
Ogre::SceneNode* buildingNode = _cityNode->createChildSceneNode(nodename.str());
// gets the assembled string from the stringstream
// null-terminated string like ogre expects
This gets you started in the right direction, but still allows for collision between child 1 and parent 10 ("citybuildingNode110") and child 11 and parent 0 (also "citybuildingNode110") and similar. So you really want something more like
nodename << childIteration << '_' << parentIteration;
to force a separator between the two numbers.
Documentation for std::stringstream.
There is also another possible nasty. The string we just supplied to ogre will only exist for as long as std::stringstream nodename exists and it will die at the end of the loop that generates it. I do not see anything in a quick perusal of the documentation that says ogre makes its own copy of this string. So play around a bit to make sure that you don't have to store this name somewhere to prevent it from falling out of scope, being destroyed, and leaving ogre with a dangling reference.
I have created a program that randomly assigns roles(jobs) to members of a certain house using file input / output.. It builds successfully, but when using cout and I actually see the results, I can see why the program is not working.
Here is the snippet of code I believe something is wrong with :
std::string foo = std::string("Preferences/") + std::to_string(members[random]) + "-Preferences";
cout << foo << endl;
And here is the members[random] array, it is randomly selecting members from this array and reviewing their available times and assigning them jobs based on their Preference input file.
unsigned const char members[22] =
{ 'a','b','c','d','e','f','g','h','i','j','k','l','m','n','o','p','q','r','s','t','u','v' };
I have created a random number picker that goes through 0-21 and assigns the value it creates to variable random. So, in essence, it is members[random] and completely random.
Here is the output I get in my terminal.
Preferences/116-Preferences
But I set the output to do Preferences/ member[random] -Preferences.
It is accessing a number and not my array chars.
I created a cout << members[random]; right below it, and every time I run the program, I get
Preferences/107-Preferences <---- A random number every time
k <---- random letter every time.
So I know it must be accessing my random functions, but assigned it to numbers! How do I fix this so my proper output can be :
Preferences/t-Preferences
Please help me, and thanks!
"The more you overthink the plumbing, the easier it is to stop up
the drain" - Scotty, Star Trek III
Declaring members to be unsigned chars does not accomplish anything useful. A simple char will suffice. std::string already implements an overloaded + operator that takes a char parameter, so it's much easier than you thought it would be:
const char members[22] = {
'a','b','c','d','e','f','g','h','i','j','k','l','m','n','o','p','q','r','s','t','u','v' };
// ...
std::string foo = std::string("Preferences/") + members[random]
+ "-Preferences";
There is no ::std::to_string(char), only (among less close) ::std::to_string(int). So your character is actually converted to its numerical representation and you get your unwanted result.
Try instead
std::string foo("Preferences/");
foo = foo.append(1, members[random]).append("-Preferences");
Variant using string streams:
ostringstream oss;
oss << "Preferences/" << members[random] << "-Preferences";
// get your string via:
oss.str();
EDIT: Problem solved! Turns out Windows 7 wont let me read/ write to files without explicitly running as administrator. So if i run as admin it works fine, if i dont i get the weird results i explain below.
I've been trying to get a part of a larger program of mine to read a file.
Despite trying multiple methods(istream::getline, std::getline, using the >> operator etc) All of them return with either /0, blank or a random number/what ever i initialised the var with.
My first thought was that the file didn't exist or couldn't be opened, however the state flags .good, .bad and .eof all indicate no problems and the file im trying to read is certainly in the same directory as the debug .exe and contains data.
I'd most like to use istream::getline to read lines into a char array, however reading lines into a string array is possible too.
My current code looks like this:
void startup::load_settings(char filename[]) //master function for opening a file.
{
int i = 0; //count variable
int num = 0; //var containing all the lines we read.
char line[5];
ifstream settings_file (settings.inf);
if (settings_file.is_open());
{
while (settings_file.good())
{
settings_file.getline(line, 5);
cout << line;
}
}
return;
}
As said above, it compiles but just puts /0 into every element of the char array much like all the other methods i've tried.
Thanks for any help.
Firstly your code is not complete, what is settings.inf ?
Secondly most probably your reading everything fine, but the way you are printing is cumbersome
cout << line; where char line[5]; be sure that the last element of the array is \0.
You can do something like this.
line[4] = '\0' or you can manually print the values of each element in array in a loop.
Also you can try printing the character codes in hex for example. Because the values (character codes) in array might be not from the visible character range of ASCII symbols. You can do it like this for example :
cout << hex << (int)line[i]
So I have a binary file that I create and initialize. If I set my pointer to seekg = 0 or seekp = 0, then I can overwrite the line of text fine. However if I jump ahead 26 bytes (the size of one line of my file and something I have certainly confirmed), it refuses to overwrite. Instead it just adds it before the binary data and pushes the old data further onto the line. I want the data completely overwritten.
char space1[2] = { ',' , ' '};
int main()
{
CarHashFile lead;
lead.createFile(8, cout);
fstream in;
char* tempS;
tempS = new char[25];
in.open("CarHash.dat", ios::binary | ios::in | ios::out);
int x = 2000;
for(int i = 0; i < 6; i++)
tempS[i] = 'a';
int T = 30;
in.seekp(26); //Start of second line
in.write(tempS, 6); //Will not delete anything, will push
in.write(space1, sizeof(space1)); //contents back
in.write((char *)(&T), sizeof(T));
in.write(space1, sizeof(space1));
in.write(tempS,6);
in.write(space1, sizeof(space1));
in.write((char *)&x, sizeof(x));
//Now we will use seekp(0) and write to the first line
//it WILL overwrite the first line perfectly fine
in.seekp(0);
in.write(tempS, 6);
in.write((char*) &x, sizeof(x));
in.write(tempS, 6);
in.write((char *) &T, sizeof(T));
return 0;
}
The CarHashFile is an outside class that creates a binary file full of the following contents when create file is invoked: "Free, " 1900 ", Black, $" 0.00f.
Everything enclosed in quotes was added as a string, 1900 as an int, and 0.00f as a float obviously. I added all of these through write, so I'm pretty sure it's an actual binary file, I just don't know why it only chooses to write over the first line. I know the file size is correct because if I set seekp = 26 it will print at the beginning of the second line and push it down. space was created to easily add the ", " combo to the file, there is also a char dol[1] = '$' array for simplicity and a char nl[1] = '\n' that lets me add a new line to the binary file (just tried removing that binary add and it forced everything onto one row, so afaik, its needed).
EDIT: Ok so, it was erasing the line all along, it just wasn't putting in a new line (kind of embarrassing). But now I can't figure out how to insert a newline into the file. I tried writing it the way I originally did with char nl[1] = { '\n' }. That worked when I first created the file, but won't afterwards. Are there any other ways to add lines? I also tried in << endl and got nothing.
I suggest taking this one step at a time. the code looks OK to me, but lack of error checking will mean any behavior could be happening.
Add error checks and reporting to all operations on in.
If that shows no issues, do a simple seek then write
result = in.pseek(26);
//print result
result = in.write("Hello World",10);
// print result
in.close();
lets know what happens
The end problem wasn't my understand of file streams. It was my lack of understanding of binary files. The newline screwed everything up royally, and while it could be added fine at one point in time, dealing with it later was a huge hassle. Once I removed that, everything else fell into place just fine. And the reason a lot of error checking or lack of closing files is there is because its just driver code. Its as bare bones as possible, I really didn't care what happened to the file at that point in time and I knew it was being opened. Why waste my time? The final version has error checks, when the main program was rewritten. And like I said, what I didn't get was binary files, not file streams. So AJ's response wasn't very useful, at all. And I had to have 25 characters as part of the assignment, no name is 25 characters long, so it gets filled up with junk. Its a byproduct of the project, nothing I can do about it, other than try and fill it with spaces, which just takes more time than skipping ahead and writing from there. So I chose to write what would probably be the average name (8 chars) and then just jump ahead 25 afterwards. The only real solution I could say that was given here was from Emile, who told me to get a Hex Editor. THAT really helped. Thanks for your time.