What is the correct method to cast an int to a void*? If that happens soon after the call to pthread_create() then you have a race condition, because there's a chance that the thread will attempt to read x's value after it's life has ended, which invokes undefined behavior. rev2023.3.3.43278. GitHub. The proper way is to cast it to another pointer type. Is pthread_join a must when using pthread in linux? Notifications. LLNL's tutorial is bad and they should feel bad. How to get the error message from the error code returned by GetLastError()? You just need to suppress the warning, and this will do it: This may offend your sensibilities, but it's very short and has no race conditions (as you'd have if you used &i). Does ZnSO4 + H2 at high pressure reverses to Zn + H2SO4? Why is there a voltage on my HDMI and coaxial cables? Staging Ground Beta 1 Recap, and Reviewers needed for Beta 2. what does it mean to convert int to void* or vice versa? The nature of simulating nature: A Q&A with IBM Quantum researcher Dr. Jamie We've added a "Necessary cookies only" option to the cookie consent popup. That's not a good idea if the original object (that was cast to void*) was an integer. I need to convert the argument to an int for later use: The compiler (GCC version 4.2.4) returns the error: You can cast it to an intptr_t type. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. Fork 63. ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ "-D_FILE_OFFSET_BITS=64" "-Wall" "-Winvalid-pch" "-g" "-Wthread-safety" "-Wno-microsoft-enum-forward-reference" "-Wno-unused-function" "-Wno-sometimes-unini To perform a cast, specify the type that you are casting to in parentheses in front of the value or variable to be converted. privacy statement. Mutually exclusive execution using std::atomic? a is of type int[4], which can be implicitly cast to int* (ie, a pointer to an int) &a is of type int(*)[4] (ie: a pointer to an array of 4 ints). Create an account to follow your favorite communities and start taking part in conversations. Replacing broken pins/legs on a DIP IC package, AC Op-amp integrator with DC Gain Control in LTspice. Did any DOS compatibility layers exist for any UNIX-like systems before DOS started to become outmoded? I have looked around and can't seem to find any information on how to do this. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. Once you manage to make this cast, then what?! How to use Slater Type Orbitals as a basis functions in matrix method correctly? But the problem has still happened. reinterpret_cast<void *>(42)). If pointers are 64 bits and ints are 32 bits, an int is too small to hold a pointer value. There is absolutely not gurantee that sizeof(int) <= sizeof(void*). If you write ((char*)ptr + 1), it will advance the pointer 1 byte, because a "char" is 1 byte. So,solution #3 works just fine. Already on GitHub? You are correct, but cocos actually only uses that address as a unique id. void* -> integer -> void* rather than integer -> void* -> integer. How do I count the number of sentences in C using ". However even though their types are different, the address is going to be the same. Using printf with a pointer to float gives an error, Meaning of int (*) (int *) = 5 (or any integer value), Casting int to void* loses precision, and what is the solution in required cases, Acidity of alcohols and basicity of amines. This is memory reinterpretation - a completely unacceptable way to do what the OP is trying to do. You cannot just cast the 32-bit variable to a pointer, because that pointer on a 64-bit machine is twice as long. Thanks for pointing that out. ", "!"? for saving RAM), use union, and make sure, if the mem address is treated as an int only if you know it was last set as an int. ../lib/odp-util.c:5834:5: error: cast to smaller integer type 'unsigned long' from 'void *' [-Werror,-Wvoid-pointer-to-int-cast] lexborisov Modest Public. If we want to get the exact value of 7/5 then we need explicit casting from int to float: Example: int x=7, y=5; However, you are also casting the result of this operation to (void*). Whats the grammar of "For those whose stories they are"? ^~~~~~~~~~~~~~~~~~~ Implementing From will result in the Into implementation but not vice-versa. Otherwise, if the original pointer value points to an object a, and there is an object b of the . Find centralized, trusted content and collaborate around the technologies you use most. On all of them int is 32bit, not 16bit. I personally upvoted this answer because by it's first line of text it helped me to understand the reason of this strange error message and what am I, poor idiot, doing :D. Not valid on Windows 64 - long is still 32-bit but pointers are 64-bit. Actions. then converted back to pointer to void, and the result will compare The subreddit for the C programming language, Press J to jump to the feed. If the sizes are different then endianess comes into play. Disconnect between goals and daily tasksIs it me, or the industry? Did any DOS compatibility layers exist for any UNIX-like systems before DOS started to become outmoded? Using Kolmogorov complexity to measure difficulty of problems? Maybe you can try this too. byte -> short -> char -> int -> long -> float -> double. Therefore it is perfectly valid for the compiler to throw an error for a line like. "I think what you should do is actually pass the address of the variable to the function" Not necessarily. you can just change architecture to support 32 bit compilation by all below in in Build Settings. Are there tables of wastage rates for different fruit and veg? But this code pass the normal variable .. On many systems, an 8-bit unsigned int can be stored at any address while an unsigned 32-bit int must be aligned on an address that is a multiple of 4. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. No sense in writing a few dozen lines of extra code just to get a bunch of numbered threads. This is what the second warning is telling you. A nit: in your version, the cast to void * is unnecessary. If you preorder a special airline meal (e.g. Most answers just try to extract 32 useless bits out of the argument. In Java, there are two types of casting: Widening Casting (automatically) - converting a smaller type to a larger type size. This will get you a pointer from a 32 bit offset: A function pointer is incompatible to void* (and any other non function pointer). Click to see the query in the CodeQL repository. Narrowing Casting (manually) - converting a larger type to a . If not, check the pointer size on your platform, define these typedefs accordingly yourself and use them. should we also have a diagnostic for the (presumed) user error? @Martin York: No, it doesn't depend on endiannness. The compiler issues the "cast from integer to pointer of different size" warning whenever the value of an integer is converted to a pointer, especially when the memory allocated to a pointer is smaller than the memory allocated to an integer data type. The difference between the phonemes /p/ and /b/ in Japanese. On most platforms pointers and longs are the same size, but ints and pointers often are not the same size on 64bit platforms. So, when you cast a (void*) to (long), you are losing 32 bits of data in the conversion. Thanks. Remembering to delete the pointer after use so that we don't leak. Staging Ground Beta 1 Recap, and Reviewers needed for Beta 2, Xcode 5 and iOS 7: Architecture and Valid architectures, xcode build error: Semantic issue cast from pointer to smaller type 'int' loses information, Issues in handling touches on subviews(uiviews) in UIScrollView, Architecture linking error after Xcode 5.1 upgrade, iOS 7.1 gives error after updating to Xcode 5.1, Linker error in Xcode 5.1 with cocos2d-x 3 beta 2. @Xax: Here's a fixed version, without the race condition: gist.github.com/depp/241d6f839b799042c409, gist.github.com/depp/3f04508a88a114734195, How Intuit democratizes AI development across teams through reusability. Making statements based on opinion; back them up with references or personal experience. How do I work around the GCC "error: cast from SourceLocation* to int loses precision" error when compiling cmockery.c? Have a question about this project? ^~~~~~~~~~~~~~~~~~~~~ In my case, I was using a 32-bit value that needed to be passed to an OpenGL function as a void * representing an offset into a buffer. How can this new ban on drag possibly be considered constitutional? But assuming that it is, as long as the caller and the callee agree, you can do that sort of thing. This is not even remotely "the correct answer". . This allows you to reinterpret the void * as an int. Making statements based on opinion; back them up with references or personal experience. What can a lawyer do if the client wants him to be acquitted of everything despite serious evidence? Does a summoned creature play immediately after being summoned by a ready action? Asking for help, clarification, or responding to other answers. @DavidHeffernan I rephrased that sentence a little. The mapping in pointer<->integer casts is implementation defined, but the intent was that if the pointer type is large enough and isn't forcefully aligned (, But that's different. Is it plausible for constructed languages to be used to affect thought and control or mold people towards desired outcomes? The nature of simulating nature: A Q&A with IBM Quantum researcher Dr. Jamie We've added a "Necessary cookies only" option to the cookie consent popup. B language was designed to develop . Can anybody explain how to pass an integer to a function which receives (void * ) as a parameter? error: cast from pointer to smaller type 'unsigned int' loses information. Pull requests. You are right! Is it possible to create a concave light? B programing language is a language based on basic combined programming or a BCPL, and it is the precursor of the C programming language. Even though what you say regarding the lifetime of the object is true, integral types are too limited for a generic API. When is casting void pointer needed in C? I understood, but that would introduce dynamic memory and ugly lifetime issues (an object allocated by one thread must be freed by some other) - all just to pass an. Thanks for contributing an answer to Stack Overflow! So reinterpret_cast has casted it to long type and then static_cast safely casts long to int, if you are ready do truncte the data. SCAN_PUT_ATTR(key, ATTR, skey, FUNC); This method will not work on 64 bit Big Endian platform, so it unnecessarily breaks portability. For integer casts in specific, using into() signals that . There is no "correct" way to store a 64-bit pointer in an 32-bit integer. Connect and share knowledge within a single location that is structured and easy to search. SCAN_PUT(ATTR, NULL); Or, they are all wrong. rev2023.3.3.43278. Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. SCAN_SINGLE("skb_priority(", uint32_t, u32, OVS_KEY_ATTR_PRIORITY); How to use Slater Type Orbitals as a basis functions in matrix method correctly? rev2023.3.3.43278. error: comparison between pointer and integer ('int' and 'string' (aka 'char *')), CS50 Caesar program is working but check50 says it isn't. I assumed that gcc makes a 65536 out of my define, but I was wrong. It's an int type guaranteed to be big enough to contain a pointer. */ >> -bool >> +enum conversion_safety >> unsafe_conversion_p (tree type, tree expr, bool . reinterpret_cast is a type of casting operator used in C++. How to tell which packages are held back due to phased updates, Identify those arcade games from a 1983 Brazilian music video. If the source type is bool, the value false is converted to zero and the value true is converted to the value one of the destination type (note that if the destination type is int, this is an integer promotion, not an integer conversion). If this is the data to a thread procedure, then you quite commonly want to pass by value. ../lib/odp-util.c:5601:9: note: expanded from macro 'SCAN_PUT' From the question I presume the OP does. Not the answer you're looking for? To subscribe to this RSS feed, copy and paste this URL into your RSS reader. 7.1 New Cast Operations The C++ standard defines new cast operations that provide finer control than previous cast operations. Connect and share knowledge within a single location that is structured and easy to search. In simple example code like this it's very easy to convince yourself that there's no problem, but in more elaborate real-world scenarios it's very easy to make this mistake inadvertently. this way I convert an int to a void* which is much better than converting a void* to an int. ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Share Improve this answer Follow answered May 6, 2018 at 7:24 Rahul If your standard library (even if it is not C99) happens to provide these types - use them. Identify those arcade games from a 1983 Brazilian music video, Relation between transaction data and transaction id, The difference between the phonemes /p/ and /b/ in Japanese. RNINGS" "-D_CRT_SECURE_NO_DEPRECATE" -MD -MQ lib/libopenvswitch.a.p/odp-util.c.obj -MF "lib\libopenvswitch.a.p\odp-util.c.obj.d" -o lib/libopenvswitch.a.p/od Terrible solution. The following behavior-changing defect reports were applied retroactively to previously published C++ standards. How create a simple program using threads in C? XCode 5.1 is change all architecture to 64 bit. Referring to N1570 7.20.1.4/p1 (Integer types capable of holding object pointers): The following type designates a signed integer type with the property It generally takes place when in an expression more than one data type is present. It's always a good practice to put your #define's in brackets to avoid such surprise. Thanks Jonathan, I was thinking about my answer in another thread: AraK is correct, passing integers a pointers are not necessarily interchangeable. tialized" "-Wno-format" "-Wno-incompatible-pointer-types" "-Werror" "-dM" "-U_MSC_VER" "-D_TIMESPEC_DEFINED" "-D_CRT_NONSTDC_NO_DEPRECATE -D_CRT_SECURE_NO_WA But, sure, in that specific case you can pass a local variable address, type casting integer to void* [duplicate]. with ids being an array of ints and touch being a pointer. Why are Suriname, Belize, and Guinea-Bissau classified as "Small Island Developing States"? AC Op-amp integrator with DC Gain Control in LTspice. "clang" "-Ilib\libopenvswitch.a.p" "-Ilib" "-I..\lib" "-I." pthread passes the argument as a void*. Basically its a better version of (void *)i. Does melting sea ices rises global sea level? Do roots of these polynomials approach the negative of the Euler-Mascheroni constant?

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