April 2003 - openSUSE Programming - openSUSE Mailing Lists

how to call linux command with java ?
by Linux Aremania 17 Apr '03

17 Apr '03

hi list, I wanna make java application which call linux command, but I don't know how to call linux command. For example : I wanna display the output of "ps -ax" command in applet. Please, I need some help here. Thx a lot ===== Linux Aremania __________________________________________________ Do you Yahoo!? The New Yahoo! Search - Faster. Easier. Bingo http://search.yahoo.com

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re[2]: [suse-programming-e] how to call linux command with java ?
by Greg Freemyer 16 Apr '03

16 Apr '03

>> On Mittwoch, 16. April 2003 15:30, Linux Aremania wrote: >> > I wanna make java application which call linux >> > command, but I don't know how to call linux command. >> > For example : I wanna display the output of "ps -ax" >> > command in applet. >> I don't program Java, but from what I know you have only very limited >> access >> to the client system in Java applets - that would be a considerable >> security >> hole. Imagine everybody who can set up a web server could run commands >> remotely on your machine over the Internet! (That would be the consequence >> of >> what you wish to do). >> Bottom line: I doubt you can do that at all in a Java applet. >> Any true expert's opinion? Signed applets may be one way to go, but I have never used them. I'm not sure how they impact the sandbox settings. Alternatively, if you have access to the client computers, you can directly open up the applets sandbox as much as you want. I support a 500 machine (win98) intranet applet based project. We edit the java.policy file on all of the client machines to enable what we need. In that file you can grant all sorts of different access rights to servlets, on a codebase by codebase basis. For instance the default java.policy file has: grant codeBase "file:${java.home}/lib/ext/*" { permission java.security.AllPermission; }; Which means any servlet launched from the above directory tree has full permissions. Greg -- Greg Freemyer

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GCC Warning: variable might be used uninitialized
by Raúl Gutiérrez Segalés 15 Apr '03

15 Apr '03

Hi, Should we always initialize our int (perhaps this applies to char as well) to something so we dont risk using it uninitialized (well at least that is what gcc warns while using to the -Wall flag) ??? ( Even though knowing our code on a normal situation it is imposible that it happens) Example: int i; int z; for(i=0;i<10;i++) { if(i==5) /* we are definitely coming in here so I have no need to give z a value*/ { z=i; printf("%d\n", z); } }

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abusive use of goto
by Raúl Gutiérrez Segalés 15 Apr '03

15 Apr '03

Hi, Today while I wwas coding I noted that I almost always use goto in this constructs: while(condition) { switch(some_var) { case 'y': do_something(); break; case 'x': goto end; break; } } end: Is this something not very advisable to do? Well at least that is what an author suggested.. in my short experience I can firmly say that it doesnt look so clean on my code..

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(slightly out of topic) libresolv
by Raúl Gutiérrez Segalés 15 Apr '03

15 Apr '03

Hi, Today I became curious of something that is completely trivial but perhaps very educational... Anybody knows if libresolv checks up the nameservers in /etc/resolv.conf everytime somebody calls gethostbyname or any other call of the family or if it has some sort of smart routine, like to make this smarter it only parses /etc/resolv.conf if its mtime has changed...

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Re: [suse-programming-e] Advice on a style issue(writing funcions)
by Nicholas Parsons 13 Apr '03

13 Apr '03

Hi all, I agree with Alan, with one added note. Its been my experience that you never want to make a source code file too big either. On some of the old UNIX C compilers, they refuse to compile these "large" source code files. So, to get around this you have to do ugly things like log in as root and use ulimit -v unlimited. Not good, especially if you are on a clients machine and don't have root access. Also avoid using global variables if at all possible. Its hard tracking down side-effects in a program if you do. Its also very hard to prove a large C program correct in that case. >This is advice that's often offered, and like all advice it >shouldn't be >followed slavishly - it really depends on the circumstances. At it's >worst >it results in horriblely dense and unreadable code as the programmer >tries to make what he wants fit into one screen. At its best it encourages programmers to think about what they are putting in to their functions. >>I would have said that a better piece of advice would be to suggest >>that >>functions should only do one thing, unless they are higher level >>functions, in which case they should call a series of functions, >>each of >>which does one thing. If you follow this, then your functions will >>generally only take up a relatively small number of lines without >>having >>to artificially squash them down. _______________________________________________ Join Excite! - http://www.excite.com The most personalized portal on the Web!

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RE: [suse-programming-e] Freeing memory
by Nicholas Parsons 13 Apr '03

13 Apr '03

Hi Rau, >>This might be an obvious question but I am a little unsure so I am >>going to go ahead and ask: Thats fine. Even a genius asks questions. >>When I create a pointer of array, and while declaring I initialize >>them, am I responsible of freeing them? No, you don't have to free them. The only time you free a pointer is after you have set it to the return value of a malloc(), realloc() or calloc() function call in C. (since I didnt have to call >>malloc I think the OS releases it..) The PROCESS is what releases/obtains memory from the OS. Normally the process obtains a certain amount of memory from the OS and sets this aside as part of the "heap". This occurs because system calls are expensive. When you call malloc() in your program for instance then the memory is allocated from the heap. If the heap gets too small as the program is running and more memory is needed, then malloc() will invoke the brk() or sbrk() system calls to obtain more memory from the Operating System. Thats why it is always wise to free() memory that you don't need anymore. When you call free() memory is returned to the heap, not the operating system per say. >>And where are they saved, in >>the heap ? >>Example: >>char mypntrs[]= { "hi", "this", "is", "a", "test" }; Not in your example. There is a syntax error there, I think you meant to say: char *mypnts[] = { "hi", "this", "is", "a", "test" }; It depends where this is declared. If you declare it as a global (outside of any function definition), then it will remain on the heap and is statically allocated at compile-time. It will not be destroyed until the program terminates. If it is declared inside a block ({}), then it is allocated/deallocated upon entry/exit of that block. This part has to do with the stack. A good book to read on this subject is a book called "The C Programming Language" by Kernighan and Richie. ~~Nick (BTW, this is in C, I guess it applies to every language, the question I mean) _______________________________________________ Join Excite! - http://www.excite.com The most personalized portal on the Web!

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Advice on a style issue(writing funcions)
by Raúl Gutiérrez Segalés 13 Apr '03

13 Apr '03

I once read an author that suggestion that one shouldnt write a function (or module) that took more then a screen(would be nice to know what resolution and letter size he meant :)) .. Now I usually write functions that take more than a screen, perhaps two or two and half and in myh opinion there is no convenient way of splitting it up or giving parts of it to another subfunction or subroutine.. Any advices for this style issue ?

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Freeing memory
by Raúl Gutiérrez Segalés 13 Apr '03

13 Apr '03

This might be an obvious question but I am a little unsure so I am going to go ahead and ask: When I create a pointer of array, and while declaring I initialize them, am I responsible of freeing them? (since I didnt have to call malloc I think the OS releases it..) And where are they saved, in the heap ? Example: char mypntrs[]= { "hi", "this", "is", "a", "test" }; (BTW, this is in C, I guess it applies to every language, the question I mean) Thanks.

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Namespaces compared to Java Packages
by Steven T. Hatton 11 Apr '03

11 Apr '03

I've had a small taste of namespace usage in C++ with the std library. I know there are some differences, but it seems C++ namespaces could be used in much the same way Java packages are used. Do people do this in C++? I haven't attempted this myself, and I haven't seen an explicit example of nested namespaces, but I have seen the scope resolution operator used twice, e.g., top::outer::inner when resolving class methods in multiple inheritance situations. Such an approach seems to work fairly well in Java. Are there reasons to use or avoid such a namespace structure in C++? Assuming it can even be done. STH

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