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  • where is c function attribute set (how to unset) with gcc

    - by cvsdave
    I am working with code from the GNU core utils, and find that the void usage() function is apparently set with the attribute "noreturn". Well, I am modifying the function, and I wish it to return (I removed the call to exit()). The compiler still complains that a "noreturn" function returns, and when using the Eclipse CDT debugger, stepping thorugh the code is anomolous - I skip over lines of code. I do not see the function be set in the .c file, and there is no .h file for this .c file. The file is df.c. I have renamed the file df_call.c. How can the compiler be finding this attribute? How can I unset it? Thanks. ======= Thanks to all contributors for their help! The short answer is "the usage() function found in GNUutils 7.4 is prototyped in system.h as 'void usage (int status) ATTRIBUTE_NORETURN'. Changing to 'void usage (int status); /*ATTRIBUTE_NORETURN;*/' resolved the issue for me, but leaves the problem of a modified system.h. The long answer is: The GNU c compiler supports assigning attributes to functions (see http://gcc.gnu.org/onlinedocs/gcc/Function-Attributes.html) one of which is "noreturn". The syntax is "attribute ((noreturn))" (see http://gcc.gnu.org/onlinedocs/gcc/Attribute-Syntax.html#Attribute-Syntax) but is often macro'd to ATTRIBUTE_NORETURN. If the attribute is set, and in this case one tries to return from the function, the executable compiles with a complaint, but compiles and runs. It will, however, behave unexpectedly (skipping over src lines in my case, maybe due to the optimization). The debugger in Eclipse CDT actually jumps past lines of code, leading the developer to doubt his senses.

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  • Saving information in the IO System

    - by djTeller
    Hi Kernel Gurus, I need to write a kernel module that simulate a "multicaster" Using the /proc file system. Basically it need to support the following scenarios: 1) allow one write access to the /proc file and many read accesses to the /proc file. 2) The module should have a buffer of the contents last successful write. Each write should be matched by a read from all reader. Consider scenario 2, a writer wrote something and there are two readers (A and B), A read the content of the buffer, and then A tried to read again, in this case it should go into a wait_queue and wait for the next message, it should not get the same buffer again. I need to keep a map of all the pid's that already read the current buffer, and in case they try to read again and the buffer was not changed, they should be blocked until there is a new buffer. I'm trying to figure it there is a way i can save that info without a map. I heard there are some redundant fields inside the I/O system the I can use to flag a process if it already read the current buffer. Can someone give me a tip where should i look for that field ? how can i save info on the current process without keeping a "map" of pid's and buffers ? Thanks!

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  • Misaligned Pointer Performance

    - by Elite Mx
    Aren't misaligned pointers (in the BEST possible case) supposed to slow down performance and in the worst case crash your program (assuming the compiler was nice enough to compile your invalid c program). Well, the following code doesn't seem to have any performance differences between the aligned and misaligned versions. Why is that? /* brutality.c */ #ifdef BRUTALITY xs = (unsigned long *) ((unsigned char *) xs + 1); #endif ... /* main.c */ #include <stdio.h> #include <stdlib.h> #define size_t_max ((size_t)-1) #define max_count(var) (size_t_max / (sizeof var)) int main(int argc, char *argv[]) { unsigned long sum, *xs, *itr, *xs_end; size_t element_count = max_count(*xs) >> 4; xs = malloc(element_count * (sizeof *xs)); if(!xs) exit(1); xs_end = xs + element_count - 1; sum = 0; for(itr = xs; itr < xs_end; itr++) *itr = 0; #include "brutality.c" itr = xs; while(itr < xs_end) sum += *itr++; printf("%lu\n", sum); /* we could free the malloc-ed memory here */ /* but we are almost done */ exit(0); } Compiled and tested on two separate machines using gcc -pedantic -Wall -O0 -std=c99 main.c for i in {0..9}; do time ./a.out; done

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  • GNU Emacs: skeleton-mode, is it still used ?

    - by xma
    Hi, given all the possible solutions to have a template system with GNU Emacs, what do people use today ? I am still using skeleton-mode but as I read it here and there, we must be really few to do so. What are you using and why ? (maybe I could switch to a more popular tool). Cheers

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  • Function pointers uasage

    - by chaitanyavarma
    Hi All, Why these two codes give the same output, Case - 1: #include <stdio.h> typedef void (*mycall) (int a ,int b); void addme(int a,int b); void mulme(int a,int b); void subme(int a,int b); main() { mycall x[10]; x[0] = &addme; x[1] = &subme; x[2] = &mulme; (x[0])(5,2); (x[1])(5,2); (x[2])(5,2); } void addme(int a, int b) { printf("the value is %d\n",(a+b)); } void mulme(int a, int b) { printf("the value is %d\n",(a*b)); } void subme(int a, int b) { printf("the value is %d\n",(a-b)); } Output: the value is 7 the value is 3 the value is 10 Case -2 : #include <stdio.h> typedef void (*mycall) (int a ,int b); void addme(int a,int b); void mulme(int a,int b); void subme(int a,int b); main() { mycall x[10]; x[0] = &addme; x[1] = &subme; x[2] = &mulme; (*x[0])(5,2); (*x[1])(5,2); (*x[2])(5,2); } void addme(int a, int b) { printf("the value is %d\n",(a+b)); } void mulme(int a, int b) { printf("the value is %d\n",(a*b)); } void subme(int a, int b) { printf("the value is %d\n",(a-b)); } Output: the value is 7 the value is 3 the value is 10

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  • How to return a value based on the type of the generic T

    - by Blankman
    I have a method like: public T Get<T>(string key) { } Now say I want to return "hello" if the type is a string, and 110011 if it is type int. how can I do that? typeof(T) doesn't seem to work. I ideally want to do a switch statement, and return something based on the Type of the generic (string/int/long/etc). Is this possible?

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  • Is an Object the smallest pageable unit in the Heap?

    - by DonnieKun
    Hi, If I have a 2 GB ram and I have an 2 instances of an Object which is 1.5 GB each, the operating system will help and context switch the pages to and from harddisk. What if I have 1 instances but is 3 GB. Can the same paging method breakdown this instances into 2 pages? Or will I encounter out-of-memory issue? Thanks.

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  • Does anybody know of a USB Postage Scale that's Linux compatible?

    - by Nick
    I'm looking for a postage scale that already has linux support (drivers, etc) for a shipping system that I'm working on. I'm planning to use Ubuntu 9.04, but I am willing to switch distro's for compatibility. Does anybody know of any scales that currently work? Is there an open source project that's working on scale drivers or similar? Thanks!

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  • Are there any scripts to synchronize sites?

    - by Matrym
    I've just set up a fail-over DNS to switch the site to a second host if the first is down. This is great for showing an old / archived version of the site, but I suspect maintenance is going to be a real pain. I moved the files over with rsync in the first place. Is this the kinda thing that could be run as a cron job, automatically moving over newer files?

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  • Function pointers usage

    - by chaitanyavarma
    Hi All, Why these two codes give the same output, Case 1: #include <stdio.h> typedef void (*mycall) (int a ,int b); void addme(int a,int b); void mulme(int a,int b); void subme(int a,int b); main() { mycall x[10]; x[0] = &addme; x[1] = &subme; x[2] = &mulme; (x[0])(5,2); (x[1])(5,2); (x[2])(5,2); } void addme(int a, int b) { printf("the value is %d\n",(a+b)); } void mulme(int a, int b) { printf("the value is %d\n",(a*b)); } void subme(int a, int b) { printf("the value is %d\n",(a-b)); } Output: the value is 7 the value is 3 the value is 10 Case 2 : #include <stdio.h> typedef void (*mycall) (int a ,int b); void addme(int a,int b); void mulme(int a,int b); void subme(int a,int b); main() { mycall x[10]; x[0] = &addme; x[1] = &subme; x[2] = &mulme; (*x[0])(5,2); (*x[1])(5,2); (*x[2])(5,2); } void addme(int a, int b) { printf("the value is %d\n",(a+b)); } void mulme(int a, int b) { printf("the value is %d\n",(a*b)); } void subme(int a, int b) { printf("the value is %d\n",(a-b)); } Output: the value is 7 the value is 3 the value is 10

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  • Difference between SET autocommit=1 and START TRANSACTION in mysql (Have I missed something?)

    - by tkolar
    Hey there, I am reading up on transactions in mysql and am not sure whether I have grasped something specific correctly, and I want to be sure I understood that correctly, so here goes. I know what a transaction is supposed to do, I'm just not sure whether I understood the statement semantics or not. So, my question is, is anything wrong, (and, if that is the case, what is wrong) with the following: By default, autocommit mode is enabled in mysql. Now, SET autocommit=0; will begin a transaction, SET autocommit=1; will implicitly commit. It is possible to COMMIT; as well as ROLLBACK;, in both of which cases autocommit is still set to 0 afterwards (and a new transaction is implicitly started). START TRANSACTION; will basically SET autocommit=0; until a COMMIT; or ROLLBACK; takes place. In other words, START TRANSACTION; and SET autocommit=0; are equivalent, except for the fact that START TRANSACTION; does the equivalent of implicitly adding a SET autocommit=0; after COMMIT; or ROLLBACK; If that is the case, I don't understand http://dev.mysql.com/doc/refman/5.5/en/set-transaction.html#isolevel_serializable - seeing as having an isolation level implies that there is a transaction, meaning that autocommit should be off anyway? And if there is another difference (other than the one described above) between beginning a transaction and setting autocommit, what is it? Thanks a lot in advance for your help!

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  • SQL Server Redirection

    - by MrTehee
    We are switching from a SQL cluster to a mirrored solution. The problem is that we have a bunch of programs that would have to switch connection strings to handle the failover. Is there any way the we can set up a redirect or proxy that would take any legacy requests and forward them to the mirrored solution?

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  • How Can I Create A Featured Content Area?

    - by ThatMacLad
    I'm working on a blog and I'd love to create a homepage with a featured post image area. I'd like it to switch between 2-3 of the latest posts images. I was wondering how I would go about doing this but so that I also have a form to update it rather than constantly editing my code.

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  • [Android] Is disabling landscape mode unforgivable?

    - by Nicolas Raoul
    Our application could support landscape mode without any problem, but it is such a pain that we are thinking about forcing portrait mode. Question: Is it BAD? The main problem is that changing orientation generates random crashes on many screens. Avoiding those crashes would potentially allow us to spend more time on the core aspects of the app. Will the same crashes happen when users switch apps anyway? Also, are there landscape-oriented devices where our app will become useless?

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  • JQuery ajax success help

    - by Jason
    Hi all, I am implementing a "Quick delete" function into a page I am creating. The way it works is like this: 1: You click the "delete" button in the table row for the record that you want to delete. 2: The page sends a request to the ajax page and return a successfully message of "yes" or a failure message of "no". My issue is that if I get a successful message of "yes" I want to hide the row for that record. I am having issue "finding" the row using JQuery. Here is my jquery code: $(document).ready(function(){ $(".pane .btn-delete").click(function(){ var element = $(this); var del_id = element.attr("id"); var dataString = 'action=del&cid=' + del_id; if(confirm("Are you sure you want to delete this content block?")) { $("#msgbox").addClass('ajaxmsg').text('Checking permissions....').fadeIn(1000); $.ajax({ type: "get", url: "ajax/admArticles_ajax.php", data: dataString, success: function(data){ switch(data) { case "yes": $("#msgbox").addClass('ajaxmsg').text('Deleting content block....').fadeIn(1000); $(this).parents(".pane").animate({ backgroundColor: "#fbc7c7" }, "fast") .animate({ opacity: "hide" }, "slow") break case "no": $("#msgbox").removeClass().addClass('error').text('You do not have the correct permissions to delete this content....').fadeIn(1000); break default: }; } }); } return false; }); }); This is the lines of code I am using to hide the row however it is not working because I don't think $(this).parents(".pane") finds the element. $(this).parents(".pane").animate({ backgroundColor: "#fbc7c7" }, "fast") .animate({ opacity: "hide" }, "slow") Any help would be greatly appreciated. Thanks...

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  • How to add an extra language input to Android?

    - by bgever
    Is it possible to add extra languages to Android? My current Android phone only supports English and Chinese language input. I would like to have Dutch also, as I can use it for word completion. The question on top of that is, how to switch easily between these languages in the text input (keyboard) GUI?

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  • Regular expression - stop at first match

    - by publicRavi
    My pattern looks something like <xxxx location="file path/level1/level2" xxxx some="xxx"> I am only interested in the part in quotes assigned to location. Shouldn't it be as easy as below without the greedy switch? Does not seem to work :( /.*location="(.*)".*/

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  • LocationMatch Regex for versioning

    - by Aventus
    I've tried using the docs but I'm quite new to regex. I've had success with others but the same method is not working for what I'm actually after. I'm trying to send users to different servers based on the version number in the URL. This this case, older versions are to be sent to the new server for a particular service. <LocationMatch "/(1.0|2.0|3.0)/appname"> ... </LocationMatch> The following is working - <LocationMatch "/1/appname"> ... </LocationMatch> <LocationMatch "/2/appname"> ... </LocationMatch> What I would love to achieve is sending all those major releases with a single tag - <LocationMatch "/(1*|2*|3*)/appname"> ... </LocationMatch> I've already referred the documentation at http://httpd.apache.org/docs/2.2/mod/core.html#locationmatch but unfortunately it doesn't cover my case with enough detail to help me.

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