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  • Remove extra junk from C preprocessor?

    - by Brendan Long
    I'm trying to use the C preprocessor on non-C code, and it works fine except for creating lines like this at the top: # 1 "test.java" # 1 "<built-in>" # 1 "<command-line>" # 1 "test.java" The problem is that these lines aren't valid in Java. Is there any way to get the preprocessor to not write this stuff? I'd prefer not to have to run this through something else to just remove the first 4 lines every time.

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  • Can I append to a preprocessor macro?

    - by JCSalomon
    Is there any way in standard C—or with GNU extensions—to append stuff to a macro definition? E.g., given a macro defined as #define quux_list X(foo) X(bar) can I append X(bas) so that it now expands as if I’d defined it #define quux_list X(foo) X(bar) X(bas)? I’m playing with discriminated/tagged unions along these lines: struct quux_foo { int x; }; struct quux_bar { char *s; }; struct quux_bas { void *p; }; enum quux_type {quux_foo, quux_bar, quux_bas}; struct quux { enum quux_type type; union { struct quux_foo foo; struct quux_bar bar; struct quux_bas bas; } t; }; I figure this is a good place for the X-macro. If I define a macro #define quux_table X(foo) X(bar) X(bas) the enumeration & structure can be defined thus, and never get out of sync: #define X(t) quux_ ## t, enum quux_type {quux_table}; #undef X #define X(t) struct quux_ ## t t; struct quux { enum quux_type type; union {quux_table} t; }; #undef X Of course, the quux_* structures can get out of sync, so I’d like to do something like this, only legally: struct quux_foo { int x; }; #define quux_table quux_table X(foo) struct quux_bar { char *s; }; #define quux_table quux_table X(bar) struct quux_bas { void *p; }; #define quux_table quux_table X(bas) (Well, what I really want to be able to do is something like member_struct(quux, foo) { int x; }; but I’m well aware that macros cannot be (re)defined from within macros.) Anyhow, that’s my motivating example. Is there a way to accomplish this? Boost.Preprocessor examples are fine, if you can show me how to make the X-macro technique work with that library.

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  • What are the lengths/limits C preprocessor as a language creation tool? Where can I learn more about

    - by Weston C
    In his FAQ @ http://www2.research.att.com/~bs/bs_faq.html#bootstrapping, Bjarne Stroustrup says: To build [Cfront, the first C++ compiler], I first used C to write a "C with Classes"-to-C preprocessor. "C with Classes" was a C dialect that became the immediate ancestor to C++... I then wrote the first version of Cfront in "C with Classes". When I read this, it piqued my interest in the C preprocessor. I'd seen its macro capabilities as suitable for simplifying common expressions but hadn't thought about its ability to significantly add to syntax and semantics on the level that I imagine bringing classes to C took. So now I have a couple of questions on my mind: 1) Are there other examples of this approach to bootstrapping a language off of C? 2) Is the source to Stroustrup's original work available anywhere? 3) Where could I learn more about the specifics of utilizing this technique? 4) What are the lengths/limits of that approach? Could one, say, create a set of preprocessor macros that let someone write in something significantly Lisp/Scheme like?

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  • Detecting login credentials abuse

    Greetings. I am the webmaster for a small, growing industrial association. Soon, I will have to implement a restricted, members-only section for the website. The problem is that our organization membership both includes big companies as well as amateur “clubs” (it's a relatively new industry…). It is clear that those clubs will share the login ID they will use to log onto our website. The problem is to detect whether one of their members will share the login credentials with people who would not normally supposed to be accessing the website (there is no objection for such a club to have all it’s members get on the website). I have thought about logging along with each sign-on the IP address as well as the OS and the browser used; if the OS/Browser stays constant and there are no more than, say, 10 different IP addresses, the account is clearly used by very few different computers. But if there are 50 OS/Browser combination and 150 different IPs, the credentials have obviously been disseminated far, and there would be then cause for action, such as modifying the password. Of course, it is extremely annoying when your password is being unilaterally changed. So, for this problem, I thought about allowing the “clubs” to manage their own list of sub-accounts, and therefore if abuse is suspected, the user responsible would be easily pinned-down, and this “sub-member” alone would face the annoyance of a password change. Question: What potential problems would anyone see with such an approach?

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  • The Bizarre Hidden Powers of the Preprocessor? [closed]

    - by ApprenticeHacker
    The preprocessor in C and C++ deserves an entire essay on its own to explore its rich possibilities for obfuscation. It is true that the C++ (and C) preprocessor can be used for a lot of powerful stuff. #ifdefs and #defines are often used to determine platforms, compilers and backends. Manipulating the code likewise. However, can anyone list some of the most powerful and bizarre things you can do with the preprocessor? The most sinister use of the preprocessor I've found is this: #ifndef DONE #ifdef TWICE // put stuff here to declare 3rd time around void g(char* str); #define DONE #else // TWICE #ifdef ONCE // put stuff here to declare 2nd time around void g(void* str); #define TWICE #else // ONCE // put stuff here to declare 1st time around void g(std::string str); #define ONCE #endif // ONCE #endif // TWICE #endif // DONE This declares different things based on how many times the header is included. Are there any other bizarre unknown powers of the C++ preprocessor?

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  • C language preprocessor behavior

    - by khanna_param
    There are different kind of macros in C language, nested macro is one of them. Considering a program with the following macro #define HYPE(x,y) (SQUR(x)+SQUR(y)) #define SQUR(x) (x*x) Using this we can successfully compile to get the result. As we all know the C preprocessor replaces all the occurrence of the identifiers with the replacement-string. Considering the above example I would like to know how many times the C preprocessor traverses the program to replace the macro with the replacement values. I assume it cannot be done in one go.

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  • What is the worst real-world macros/pre-processor abuse you've ever come across?

    - by Trevor Boyd Smith
    What is the worst real-world macros/pre-processor abuse you've ever come across (please no contrived IOCCC answers *haha*)? Please add a short snippet or story if it is really entertaining. The goal is to teach something instead of always telling people "never use macros". p.s.: I've used macros before... but usually I get rid of them eventually when I have a "real" solution (even if the real solution is inlined so it becomes similar to a macro). Bonus: Give an example where the macro was really was better than a not-macro solution. Related question: When are C++ macros beneficial?

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  • Visual C++ preprocessor definitions

    - by alemjerus
    Is there a way to transfer C++ preprocessor definitions into a custom pre-link step procedure call as a command-line parameter or export them into a file any other way? Example: Let's say, I have a c++ project, and in it's Debug configuration I put a preprocessor definition like MAKUMBA_OBA=0x13 Then I add custom pre-link step which executes some javascript like sarahjessicaparker.js /to tomsrhinoplasty $(MAKUMBA_OBA) It would be great, if it just worked, but I never get a third parameter in my js. So the question is: how to pass a preprocessor definition to s script?

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  • Documenting preprocessor defines in Doxygen

    - by Fire Lancer
    Is it possible to document preprocessor defines in Doxygen? I expected to be able to do it just like a variable or function, however the Doxygen output appears to have "lost" the documentation for the define, and does not contain the define its self either. I tried the following /**My Preprocessor Macro.*/ #define TEST_DEFINE(x) (x*x) and /**@def TEST_DEFINE My Preprocessor Macro. */ #define TEST_DEFINE(x) (x*x) I also tried putting them within a group (tried defgroup, addtogroup and ingroup) rather than just at the "file scope" however that had no effect either (although other items in the group were documented as intended). I looked through the various Doxygen options, but couldn't see anything that would enable (or prevent) the documentation of defines.

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  • Detecting abuse for post rating system

    - by Steven smethurst
    I am using a wordpress plugin called "GD Star Rating" to allow my users to vote on stories that I post to one of my websites. http://everydayfiction.com/ Recently we have been having a lot of abuse of the system. Stories that have obviously been voted up artificially. "GD Star Rating" creates some detailed logs when a user votes on a story. Including; IP, Time of vote, and user_adgent, ect.. For example this story has 181 votes with an average of 5.7 http://www.everydayfiction.com/snowman-by-shaun-simon/ Most other stories only get around ~40 votes each day. At first I thought that the story got on to a social bookmarking site Digg, Stumbleupon ect... but after checking the logs I found that this story is getting the same amount of traffic that a normal story gets ~2k-3k. I checked if all the votes for this perpendicular story where coming from a the same IP address. I could see this happening if a user was at a school's computer lab using all their lab computers to vote up this story. Not one duplicate IP address in the log for this story. SELECT ip, COUNT(*) as count FROM wp_gdsr_votes_log WHERE id=3932 GROUP BY (ip ) ORDER BY count DESC Next I thought that a use might be using a proxy to vote up a story. I checked this by grouping all the browser user_agent together to see if there a single browser voting in a perpendicular way. At most 7 users where using a similar browser but voted sporadically (1-5), no evidence of wrong doing. SELECT user_agent, COUNT(*) as count FROM wp_gdsr_votes_log WHERE id=3932 GROUP BY ( user_agent) ORDER BY count DESC I check was to see if all the votes came in at a once. Maybe someone has a really interesting bot that can change the user_adgent and uses proxies, ect... At most 5 votes came with in 2 mins of each other. It doesn't seem to be any regularity on how people vote (IE a 5 vote does not come in once a min) SELECT * FROM wp_gdsr_votes_log WHERE id =3932 AND vote=5 ORDER BY wp_gdsr_votes_log.voted DESC The obvious solution to this problem is to force people to login before they are allowed to vote. But I would prefer to not have to go down that route unless it is absolutely necessary. I'm looking for suggestions on things to test for to detect the abuse.

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  • C++ Preprocessor string literal concatenation

    - by ezpz
    I found this regarding how the C preprocessor should handle string literal concatenation (phase 6). However, I can not find anything regarding how this is handled in C++ (does C++ use the C preprocessor?). The reason I ask is that I have the following: const char * Foo::encoding = "\0" "1234567890\0abcdefg"; where encoding is a static member of class Foo. Without the availability of concatenation I wouldnt be able to write that sequence of characters like that. const char * Foo::encoding = "\01234567890\0abcdefg"; Is something entirely different due to the way \012 is interpreted. I dont have access to multiple platforms and I'm curious how confident I should be that the above is always handled correctly - i.e. I will always get { 0, '1', '2', '3', ... }

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  • C language preprocessor behavior

    - by khanna_param
    There are different kind of macros in C language, nested macro is one of them. Considering a program with the following macro #define HYPE(x,y) (SQUR(x)+SQUR(y)) #define SQUR(x) (x*x) Using this we can successfully compile to get the result. As we all know the C preprocessor replaces all the occurrence of the identifiers with the replacement-string. Considering the above example I would like to know how many times the C preprocessor traverses the program to replace the macro with the replacement values. I assume it cannot be done in one go.

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  • Use a template parameter in a preprocessor directive?

    - by Ranju V
    Is it possible to use a non-type constant template parameter in a preprocessor directive? Here's what I have in mind: template <int DING> struct Foo { enum { DOO = DING }; }; template <typename T> struct Blah { void DoIt() { #if (T::Doo & 0x010) // somecode here #endif } }; When I try this with something like Blah<Foo<0xFFFF>>, VC++ 2010 complains something about unmatched parentheses in the line where we are trying to use "#if". I am guessing the preprocessor doesn't really know anything about templates and this sort of thing just isn't in its domain. What say? Thanks!

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  • Writing preprocessor directives to get string

    - by Dave18
    Can you write preprocessor directives to return you a std::string or char*? For example: In case of integers: #define square(x) (x*x) int main() { int x = square(5); } I'm looking to do the same but with strings like a switch-case pattern. if pass 1 it should return "One" and 2 for "Two" so on..

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  • Mimic C preprocessor with Python/Ruby?

    - by prosseek
    I need to mimic the preprocessor feature of C with Python. If I want to run the debug release, I use as follows with C #ifdef DEBUG printf(...) #endif I just use -DDEBUG or similar to trigger it on or off. What method can I use for Python/Ruby? I mean, what should I do to control the behavior of python/ruby scripts in such a way that I can change a variable that affects all the script files in a project?

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  • gcc run "light" preprocessor

    - by Claudiu
    Is there any way to run the gcc preprocessor, but only for user-defined macros? I have a few one-liners and some #ifdef etc... conditionals, and I want to see what my code looks like when just those are expanded. As it is, the includes get expanded, my fprintf(stderr)s turn into fprintf(((__getreeent())-_stderr), etc...

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  • C preprocessor: using #if inside #define?

    - by Wxy
    I want to write a macro that spits out code based on the boolean value of its parameter. So say DEF_CONST(true) should be expanded into "const", and DEF_CONST(false) should be expanded into nothing. Clearly the following doesn't work because we can't use another preprocessor inside #defines: #define DEF_CONST(b_const) \ #if (b_const) \ const \ #endif Any idea about how to do it?

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  • How to use Preprocessor directives in MVC aspx pages

    - by Zuber
    I am using MinifyJS.tt which is a T4 template to minify all my JS files automatically. In my aspx files, I am referencing all the javascript files. Now, I want to add a condition (maybe compiler directive) to use the original JS file when I am debugging the application, and to use the minified JS files when I simply run the application without debug. I tried using #if in the aspx page, but that did not seem to work. Can we make use of preprocessor directives in aspx pages? Is there an alternative way to achieve my goal?

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  • Can I see shader preprocessor output?

    - by GLaddict
    I am using #defines, which I pass runtime to my shader sources based on program state, to optimize my huge shaders to be less complex. I would like to write the optimized shader to a file so that next time I run my program, I do not have to pass the #defines again, but I can straight compile the optimized shaders during program startup because now I know what kind of shaders by program needs. Is there a way to get the result from shader preprocessor? I can of course store the #define values to a file and based on that compile the shaders during program startup but that would not be as elegant.

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  • Preprocessor Conditionals

    - by Mike
    I was wondering if it would be possible to have a define which changes values at some point in the code be used in a conditional. Basically something like this: //////////////////////////////////////////// SomeFile.cpp #define SHUTDOWN false while(window->isOpen()) { if(SHUTDOWN) window->close(); // Rest of the main loop } //////////////////////////////////////////// SomeOtherFile.cpp if(Escape.isPressed()) { #undef SHUTDOWN #define SHUTDOWN true } Thus causing the app to close. If it's not, would having a function like RenderWindow* getWindow() { return window; } and then calling if(Escape.isPressed()) getWindow()->close(); The best way to do it? I'd rather not go that route because the classes that are calling the key event are members of the class controlling the main loop and the window, so I'd have to set pointers to the containing class in the smaller classes to call getWindow() and it just seems like a more complicated method. But if I can't do it with preprocessor directives I'll just have to use pointers to the parent class.

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