Programming :: Child Classes That Extend Each Type Of Pet
Jan 6, 2011
I am fairly new to c++. There must be a better way to do the following?:- Say I have a base class, Pet. I have several child classes that extend from this, like Dog, Cat, Fish etc.
I have the following function, that returns a pointer to a new Pet:-
Code: Pet* addPetToVet()
{ //Do some stuff
return new Pet();
} This will return a pointer an instance of a pet object.
Now, if I want to interpret this pet as a dog or cat I have to do this:-
Code: Dog* dogA = static_cast<Dog*>(addPetToVet());
Cat* catA = static_cast<Cat*>(addPetToVet()); Is there a way around this? Casting seems lame. I cant write a function for each type of pet.
I have a doubt about signals in C programming. I have done this little program to explain it. It creates a child process with fork and, when the child ends, receives the SIGCHLD signal and wait for its termination.Ok, quite easy, BUT when I execute this code the SIGCHLD signal is received twice, first as an error (returns -1) and the second one to finish the child process.I don't understand the meaning of the first received signal. Why is it generated? Is the code wrong? (if you add the SIGINT and press Ctrl+C during the execution it also receives two signals instead of one)
When I start Firefox I get the subject error. Suse 11.2. What does it mean, and how can I fix it? It also says "[java script application]" in the task bar when FF launches.
I have a desktop with Ubuntu on it that will be used by children for internet access and the parents of those who will be using it would like that some sort of basic child protection software was installed on it so that those using the computer don't accidentally or even deliberately out of curiosity access adult material.Is there a decent easy to use Ubuntu software out there that allows for parental control over what kind of websites can be accessed by children?
Parent: chid_pid=4356 i=0 parent's pid=4355 This is child 4356 i=0 This is child 4357 i=1
[code]....
I can observe instead of two children(as I expect) processes there are three. This is because child process 4356 creates its own child. Why all the messages of the type "This is child X i=Y" are concentrated one under another? How exactly fork works? Is affected by the fact that I have a dual-core processor?
I know the basic answer about how to create a class as ABC.But I don;'t know- - why I have to create a AbstractBaseClass. - In what situations it can be used.an example code base and not like a animal(base) and tiger(derived) relationship example.
This is probably a really stupid thing to ask considering the development I'm doing (effectivly creating a virus scanner), but how do I link classes/cpp files?I have 3 applications/sections that I can compile/combine with a makefile, that's fine, but I need them to run 1, 2, 3 once the output from the makefile is done.Currently the only section to actually run is whichever I have "main" in and obviously if I put that into all three, they won't compile as one.I've been looking all over the place at all sorts, header files and such, but there is no mention of how toually do this although I'm sure it must be possible. I'm used to being able to do this in Java and I'm sure I've seen C++ applications do it, but not worked out how.I have 3x .cpp files which are combined into one using a makefile:
Is it possible to have a templated c++ stl container in another class without specifying the type prior to compile time? I haven't coded in c++ in a while and im at a total loss.
For example - Not real code. Just outlining the problem code...
I'm new to Java. I'm trying to use some dynamically loaded classes in my application. The application doesn't know those classes , Just it try to load a class by name that its name came from input. It doesn't know class (So I can't use casting) but just needs to call some methods of that class (every class should have that methods). I thought about interfaces but I don't know how. How can I call those methods?
Why are the 'defense' method calls actually using the 'offense' methods.Also, is there a way to remove the commented base classes for 'Player' so that the casting isn't necessary?
I've got a set of objects (all of the same type). I'm trying to think of a good way to divide it into equivalence classes, with equivalence of two objects defined as meaning a specified set of attributes are equal for both objects. More concretely, I've got:
- a Java class with around 50 fields - a bunch of instances of the class
I want:
- to divide the instances into a few sets - in each set, each instance has field 1 - field 5 equal to fields 1-5 of the other instances in the set.
The method I've come up with is to generate a hashcode for each instance based on the hashcodes of fields 1-5*, and map the hashcode to one of my sets. Ignoring problems with potential hashcode collisions (which I'm expecting to be too rare to worry about for now), does that sound reasonable? It seems simple enough, but I'm wondering if there's a simpler method I haven't thought of.
* I'll generate the hashcode using a method based on Eclipse's generic hashcode method, which looks like this:
Code:
public int hashCode() { final int prime = 31; int result = 1;
I was wondering if 7735, 7736, 7737, 7743 were really processes. Then I checked /proc, I could cd to /proc/7735, /proc/7736, etc, but I could not ls them out. I looked at the man page of "pstree", it says,
Code:
Child threads of a process are found under the parent process and are shown with the process name in curly braces, e.g.
icecast2---13*[{icecast2}]
So, what does all this mean? Does it mean that 7735, 7736, 7737, 7743 are just threads but not processes? If so, why could I cd to /proc/<id> but not see them in "ps -elf".
Now,I created one parent and two children. I must create some value as random in child1 and child1 has to send these values to child2.Child2 must read them.. now,I cant create some random values and i can send them.But child2 doesnt work. I have two functions. One them is writing, another one is reading. Child2 uses reading function,but it doesnt work (child2 cant call it, because writing function in endless loop) What i must do? I used wait,usleep... No way.. I attached my file and also there is code..
I want to extend my perl capabilities using CGI. So, could you please tell me where to start and how to start my cgi scripts on linux RHEL AS 4 system.
I have a root process (on linux) that forks a child and the child process then drops privileges by doing a setuid() to a normal user. After the child setuid()'s, it is of course impossible for it to gain root again by itself. But since the main process is still running as root, i was wondering if there was a simple/smart way of getting the root-master-process to elevate the child back to root (or maybe just to another non-privi uid). Is there some way to do a setuid() on another pid? or maybe something can be done through /proc/<pid>/? Killing the child is not an option (because its what it does today and im trying to find a smarter way). (The program is apache2's mpm-itk worker and the "child" is the actual apache2 process serving a page.)
I work on Linux for ARM processor for cable modem. There is a tool that I have written (as the job demands) that sends/storms customized UDP packets using raw sockets. I form the packet from scratch so that we have the flexibility to play with different options. This tool is mainly for stress testing routers.
The details are here.
I actually have multiple interfaces created. Each interface will obtain IP addresses using DHCP. This is done in order to make the modem behave as virtual customer premises equipment (vcpe).
When the system comes up, I start those processes that are asked to. Every process that I start will continuously send packets. So process 0 will send packets using interface 0 and so on. Each of these processes that send packets would allow configuration (change in UDP parameters and other options at run time). Thats the reason I decide to have separate processes.
I start these processes using fork and excec from the provisioning processes of the modem.
The problem now is that each process takes up a lot of memory. Starting just 3 such processes, causes the system to crash and reboot.
I have tried the following:- 1-I have always assumed that pushing more code to the Shared Libraries will help. So when I tried moving many functions into shared library and keeping minimum code in the processes, it made no difference to my surprise.
2-I also removed all arrays and made them use the heap. However it made no difference. This maybe because the processes runs continuously and it makes no difference if it is stack or heap?
3-I suspect the process from I where I call the fork is huge and that is the reason for the processes that I make result being huge. I am not sure how else I could go about. say process A is huge -> I start process B by forking and excec. B inherits A's memory area. So now I do this -> A starts C which inturn starts B will also not help as C still inherits A?. I used vfork as an alternative which did not help either. I do wonder why.
reduce the memory used by each independent child processes.
the wrong part of the forum but basically im working on a project and getting no where what so ever and i was wondering if i could get your help. Basically i have to create two scripts do:
The parent script which is going to: o spawn several child processes. o keep track of the progress of the child processes.
Im using gdb for debugging my application.. I was able to debug child process(when fork comes) .. and in child process we have an exec call to .... So the problem is, when the control come to exec , the exec process is executing at a time... I could not debug the exec. process... error is stack curruption due to same frame So, is there any way to debug the exec process
I'm writing a sort of toy shell using fork() and execv(). It runs smoothly enough untill the user enters an invalid command at which point the program hangs, so I need a way to check if the program loaded using execv returned correclty or not in the parent process and kill it if it didntI tried writing stderr to a text file to see if something whent wrong but doesnt really work out. Try running ./digenv GDM -i -Q for instance. (-Q is an invalid option for grep which the program runs at a certain point).Heres the code:
I'm trying to write a shell script that do ftp and download file periodically, this script should be called by a daemon running in the background.
the shell script "script.sh" is as follows:
Code: yafc ftp://test:test@192.168.1.225:21 < commands and the "commands" files is
Code: d Root/md5* / quit
if I run script.sh it will work just fine. But when the daemon software calls the "script.sh", the script will send ftp login request to the ftp server, but will not even answer the username or anything.
I believe it is something about child process redirection, but I don't know how to deal with it.
This problem is not only with yafc, it is the same with any ftp client or any application like telnet and so.
If a process forks its child and communicate with the child using pipe, do closing the write end of the pipe and terminating the writing process have the same effect?
what I am trying to do is to pass an argument to the standard input stream of a child process. I mean I create two programs .. first one invokes the other. second one contains something like
Code:
scanf("%d", &n);
now I want my first program to be able to pass a value to the second one so that it gets stored in n.
One requirement of a project I am currently working on (for Maemo) is that the Qt application displays a QSplashScreen when it loads.
My issue is that the application is fairly small and I have written it to load components etc as they are required rather than at start-up. This has lead to quick start up times (which, in a perfect world is what we all strive for!)
How would I intentionally delay the start-up time so that the splash shows for longer?
I have investigated
Quote:
QTimer:: oneShot() (Space added to prevent smiley)
however, its prototype dictates that it be connected to a slot. I am running this QSplashScreen from inside main so this is neither needed nor feasible.
What is the best way to essentially do this:
Code: Display Splash Timer for 3 seconds Close Splash Display mainWindow
I do not want to use native system calls such as sleep() and would instead rather a Qt based solution.
I'm in the process of writing a program that is a server- it will accept connections and stuff, and spawn a child process for each. However, i've run into a small problem. I do NOT want to bother with keeping track of the processes unless i need to. So, i set SA_NOCLDWAIT (#ifdef) on a SIG_IGN to the SIGCHLD handler through sigaction interface. The standard says that it the kernel will then keep track of reaping zombie processes for me (a HUGE plus). However, upon receiving a SIGINT signal, i want to stop the server from accepting new connections (done), and then wait for there to be no new connections. I was thinking of just putting a loop like so:
However, I'm not *sure* that this will work, especially with SIGCHLD still ignored. So how can i tell if there are still child processes? I can't find any call like int getnumchld(pid_t proc); (i wish). Plus it would be inefficient to spin on that function anyway. OTOH, i would rather *NOT* have to do the same thing in a loop with a system("ps |...>file"); read(file); etc. either. Is there a way i can portably implement this feature (I was hoping i could run it on linux and the major BSDs, at least).
TO SUM IT UP:
How can i tell if a process has no child processes if i've SIG_IGN'd SA_NOCLDWAIT'd the SIGCHLD? Is there a _reasonably_ portable way to do so? I *don't* want to manually wait for EVERY process. Maybe only those still active at the time of SIGTERM, but that requires keeping track of the number of connections and whether those have terminated...
EDIT: Does anyone know if the above code *would* work, even with SIGCHLD ignored and the kernel cleaning up zombies *for* me? I checked the manpage and it doesn't say much.
EDIT1: Note that all of the processes are in the same process group and session. SO i can find them through this as well. Perhaps even setting the uid/gid and finding all processes run by that group?
EDIT2: i have an idea if the above isn't feasible. If there is no "elegant" way to do it, i could reduce the complexity by sending a SIGUSR1 to the whole process group. Each process would then set a flag telling it to send a SIGUSR1 in reply and send a SIGUSR2 when it is done executing. Then i could keep a count of signals. Maybe that would be *easier*. Or perhaps a count of all child processes and just a termination signal to decrement the counter.
i need C code to get child pids from its parent pid in linux and in kernel mode, is there anything like getpid() or getppid() which works in kernel mode?
I'm looking for a way in Perl to be able to take a list of servers, ssh multiple commands to it and store the results. If I do this process serially, sometimes one server will hang the whole script and if it doesn't, it still takes hours to complete.
I'm thinking what I need to do is make a parent loop that calls out a separate process that passes the server name to the child sub process and then executes all the commands I have defined in its own process. If one server 'hangs', at least that won't stop the script from doing all the other servers in the list.
I'm guessing using the fork() command would serve me best, however, all the online descriptions I have found have been vague at best.
I am writing a perl script where forking a child and the child is waiting for some response from C++ exe. Here is the code snippet:
Code: my $retPid = fork; if ($retPid) { # I am parent ... # Install signal handler $SIG{CHLD} = &REAPER; ... # sleep for a week (6 hours at a time) for ($cnt = 0; $cnt < 28 ; $cnt++) { select(undef, undef, undef, 21600); last if ( ! -e "/proc/$retPid" ); } ... } else { # I am child ($iid, $rc, %data) = $cpp_exe->getResponse(604800); # 1 week timeout ... }
If the cpp_exe takes very long time (around 30 hours) to respond then the perl script (both parent and child) is dieing. The SIG{CHLD} handler defined in parent is not getting called. It seems parent is dieing first then child is dieing (or may be both dieing at the same time). Why the script is dieing?
i got basic knowledge about creating a single child from a parent using fork(). But when it comes into creating multiple children, i am simply stuck. I am trying to create two processes from a parent and it would wait for both two processes to finish. my attempt is as below
