Share Improve this answer Follow answered May 6, 2018 at 7:24 Rahul I have a function with prototype void* myFcn(void* arg) which is used as the starting point for a pthread. this way I convert an int to a void* which is much better than converting a void* to an int. If it's anything like cocos2d-iphone v2.x and just based on this slice of code in a core class I wager it's safe to say that cocos2d-x 2.x also is not compatible with 64 bit code, and you can expect all kinds of issues (not just compile-time but also runtime). The reinterpret_cast makes the int the size of a pointer and the warning will stop. The preprocesor absolutely will not perform arithmetic. /** Dynamically allocate a 2d (x*y) array of elements of size _size_ bytes. this question. The result is implementation-defined and typically yields the numeric address of the byte in memory that the pointer pointers to. As with all cast expressions, the result is: Two objects a and b are pointer-interconvertible if: static_cast may also be used to disambiguate function overloads by performing a function-to-pointer conversion to specific type, as in. Connect and share knowledge within a single location that is structured and easy to search. You are getting warnings due to casting a void* to a type of a different size. What is the point of Thrower's Bandolier? Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. Using Kolmogorov complexity to measure difficulty of problems? Recovering from a blunder I made while emailing a professor. pthread create managing values generated in function (in c), Establishing TCP socket connection between PHP client and C server on Ubuntu. You are just making it bigger by tricking the compiler and the ABI. Remarks. The following program casts a double to an int. Error while setting app icon and launch image in xcode 5.1. 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. For a fairly recent compiler (that supports C99) you should not store or represent address as plain int value. reinterpret_cast<void *>(42)). Any expression can be cast to type void (which means that the result of the expression is ignored), but it's not legal to cast an expression of type void to type int not least because the result of such a cast wouldn't make any sense. linux c-pthreads: problem with local variables. An open (void) pointer can hold a pointer of any type. 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 SQL Server does not automatically promote . I am compiling this program in linux gcc compiler.. Use returnPtr[j] = (void *) ((long)ptr + i); ). No idea how it amassed 27 upvotes?! So the compiler is very picky here and the correct solution to make the code compile again and still let it show the exact same behavior like in Xcode 5.0 is to first cast to an integer type with a size that matches the one of a pointer and to then do a second cast to the int that we actually want: ids [i] = (int) (size_t)touch; How Intuit democratizes AI development across teams through reusability. ^~~~~~~~~~~~~~~~~~~~ Unless you have a valid address at that value, you are going to invoke undefined behaviour when try to use that pointer. Acidity of alcohols and basicity of amines. I wish that you write those answer first than the explanation. What Is the Difference Between 'Man' And 'Son of Man' in Num 23:19? However, you are also casting the result of this operation to (void*). FAILED: lib/libopenvswitch.a.p/odp-util.c.obj ERROR: incompatible integer to pointer conversion assigning to 'string' (aka 'char *') from 'int', error: cast to 'string' (aka 'char *') from smaller integer type 'int' [-Werror,-Wint-to-pointer-cast], error: incompatible integer to pointer conversion assigning to 'string' (aka 'char *') from 'int' C, warning: initialization of 'unsigned char' from 'uint8_t *' {aka 'unsigned char *'} makes integer from pointer without a cast [-Wint-conversion], Minimising the environmental effects of my dyson brain. Does melting sea ices rises global sea level? Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. For the second example you can make sure that sizeof (int) <= sizeof (void *) by using a static_assert -- this way at least you'll get a notice about it. You may declare a const int variable and cast its reference to the void*. In such a case the programmer can use a void pointer to point to the location of the unknown data type. However even though their types are different, the address is going to be the same. 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. Pd = Pa; Similarly, Pc may be type cast to type int and assigned the value Pa. 1. [that could be a TODO - not to delay solving the ICE]. Did any DOS compatibility layers exist for any UNIX-like systems before DOS started to become outmoded? Euler: A baby on his lap, a cat on his back thats how he wrote his immortal works (origin?). ../lib/odp-util.c:5665:7: note: expanded from macro 'SCAN_SINGLE' Usually that means the pointer is allocated with. this way you won't get any warning. On a 64-bit Windows computer, 'long' is a 32-bit type, and all pointers are 64-bit types. Apparently the clang version in Xcode 5.1 and above is more strict about potential 32bit vs. 64 bit incompatibilities in source code than older clang versions have been. ), For those who are interested. I think the solution 3> should be the correct one. The difference between the phonemes /p/ and /b/ in Japanese, Styling contours by colour and by line thickness in QGIS, AC Op-amp integrator with DC Gain Control in LTspice, Identify those arcade games from a 1983 Brazilian music video. That's not a good idea if the original object (that was cast to void*) was an integer. Otherwise, if the original pointer value points to an object a, and there is an object b of the . whether it was an actual problem is a different matter though. For the second example you can make sure that sizeof(int) <= sizeof(void *) by using a static_assert -- this way at least you'll get a notice about it. @Martin York: No, it doesn't depend on endiannness. ../lib/odp-util.c:5665:7: note: expanded from macro 'SCAN_SINGLE' Why is there a voltage on my HDMI and coaxial cables? You can use any other pointer, or you can use (size_t), which is 64 bits. You can convert the values from one type to another explicitly using the cast operator as follows (type_name) expression And in this context, it is very very very common to see programmers lazily type cast the. (int) pthread_self() 64int48intuintptr_t (unsigned int) you can pass the int value as void pointer like (void *)&n where n is integer, and in the function accept void pointer as parameter like void foo(void *n);and finally inside the function convert void pointer to int like, int num = *(int *)n;. ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Note the difference between the type casting of a variable and type casting of a pointer. Replacing broken pins/legs on a DIP IC package, How to handle a hobby that makes income in US. 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; what happens when we typecast normal variable to void* or any pointer variable? 7.1 New Cast Operations The C++ standard defines new cast operations that provide finer control than previous cast operations. Staging Ground Beta 1 Recap, and Reviewers needed for Beta 2, error: cast from void* to int loses precision, cast to pointer from integer of different size, pthread code. 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). Infact I know several systems where that does not hold. What video game is Charlie playing in Poker Face S01E07? To learn more, see our tips on writing great answers. The program can be set in such a way to ask the user to inform the type of data and . @jackdoe: It's a waste of human life to write code that "you may need in the future". Staging Ground Beta 1 Recap, and Reviewers needed for Beta 2. The calculated expression consists of two operations. This forum has migrated to Microsoft Q&A. What I am saying is that it would be safer to use new(5) rather than 5 and deal with it appropriately at the other end. He should pass the address of the integer, the thread should get that address, Note: This is only appropriate is you cast the. Bulk update symbol size units from mm to map units in rule-based symbology. The code ((void*)ptr + 1) does not work, because the compiler has no idea what size "void" is, and therefore doesn't know how many bytes to add. @BlueMoon Thanks a lot! This is flat out wrong. Whats the grammar of "For those whose stories they are"? ^~~~~~~~~~~~~~~~~~~~~ Why is this sentence from The Great Gatsby grammatical? Please unaccept the answer you have chosen as it is wrong (as the comments below it say) and will lead to bugs. A missing cast in the new fast > enumeration code. ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~. ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ cast to 'double *' from smaller integer type 'unsigned int' The C compiler is gcc, clang version 3.9.1, target aarch64--linux-android, thread model posix. What does casting to void* does when passing arguments to variadic functions? If the sizes are different then endianess comes into play. By clicking Sign up for GitHub, you agree to our terms of service and The dynamic_cast<>operator provides a way to check the actual type of a pointer to a polymorphic class. C++ how to get the address stored in a void pointer? The OP wanted to convert a pointer value to a int value, instead, most the answers, one way or the other, tried to wrongly convert the content of arg points to to a int value. rev2023.3.3.43278. Basically its a better version of (void *)i. byte -> short -> char -> int -> long -> float -> double. Thank you all for your feedback. This method will not work on 64 bit Big Endian platform, so it unnecessarily breaks portability. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide. How can this new ban on drag possibly be considered constitutional? I'm only guessing here, but I think what you are supposed to do is actually pass the address of the variable to the function. So make sure you understand what you are doing! Sign in itch" "-I..\include\windows" "-Iinclude" "-I..\include" "-I..\datapath-windows\include" "-IC:\PTHREADS-BUILT\include" "-Xclang" "-fcolor-diagnostics" "-pipe" Where does this (supposedly) Gibson quote come from? @DavidHeffernan, sane thread APIs wouldn't send integral data to the thread procedures, they would send pointers. } SCAN_END_SINGLE(ATTR) You can only do this if you use a synchronization primitive to ensure that there is no race condition. You think by casting it here that you are avoiding the problem! No sense in writing a few dozen lines of extra code just to get a bunch of numbered threads. The bigint data type is intended for use when integer values might exceed the range that is supported by the int data type.. bigint fits between smallmoney and int in the data type precedence chart.. Actions. @DavidHeffernan I rephrased that sentence a little. A long long would not work for 32bit systems and a long would not work for 64 bit Windows (while 64bit Unix and Unix-like systems like OS X use the LP64 data model, in which a long is 64bit, 64bit Windows uses the LLP64 data model, in which a long has a size of 32bit (http://en.wikipedia.org/wiki/64-bit_computing#64-bit_data_models)). GitHub. Staging Ground Beta 1 Recap, and Reviewers needed for Beta 2. what does it mean to convert int to void* or vice versa? ../lib/odp-util.c:5603:13: note: expanded from macro 'SCAN_PUT' That's probably going to be true for most platforms you will ever encounter, but it's not a guarantee; it's implementation-dependent. Thanks for contributing an answer to Stack Overflow! casting from int to void* and back to int. and how to print the thread id of 2d array argument? In the best case this will give the same results as the original code, with no advantages, but in the worst case it will fail in multiple catastrophic ways (type punning, endianness, less efficient, etc. So the compiler is very picky here and the correct solution to make the code compile again and still let it show the exact same behavior like in Xcode 5.0 is to first cast to an integer type with a size that matches the one of a pointer and to then do a second cast to the int that we actually want: I am using size_t here, because it is always having the same size as a pointer, no matter the platform. As a result of the integer division 3/2 we get the value 1, which is of the int type. And then assign it to the double variable. For integer casts in specific, using into() signals that . Where does this (supposedly) Gibson quote come from? And in the function you get the value of the pointer by using the dereference operator *: Please read why glib provide macros for this kind of conversions, there's no need to repeat the text here. Euler: A baby on his lap, a cat on his back thats how he wrote his immortal works (origin? If you really need such trickery, then consider one of dedicated types, which are intptr_t and uintptr_t. Mutually exclusive execution using std::atomic? How to correctly cast a pointer to int in a 64-bit application? The best way is, if one can, do not do such casting, instead, if the same memory address has to be shared for pointer and int (e.g. Disconnect between goals and daily tasksIs it me, or the industry? Making statements based on opinion; back them up with references or personal experience. Find centralized, trusted content and collaborate around the technologies you use most. Does Counterspell prevent from any further spells being cast on a given turn? Note:You might receive a runtime exception if the pointer contains a value unsuitable for the context. This is not even remotely "the correct answer". But gcc always give me a warning, that i cannot cast an int to a void*. Do roots of these polynomials approach the negative of the Euler-Mascheroni constant? The most general answer is - in no way. ^~~~~~~~~~~~~~~~~~~ Thus as a result it may be less error prone to generate a pointer dynamcially and use that. static const void* M_OFFSET = (void*)64*1024; Since gcc compiles that you are performing arithmetic between void* and an int ( 1024 ). (Also, check out how it prints "5" twice), passing a unique pointer to each thread wont race, and you can get/save any kind of information in the th struct. What is the purpose of non-series Shimano components? Even if you are compiling your program for a 32-bit computer, you should fix your code to remove these warnings, to ensure your code is easily portable to 64-bit. I'm unfamiliar with XCode, but the solution should be something like follows: Most of the "solutions" above can lose part of the pointer address when casting to a smaller type. vegan) just to try it, does this inconvenience the caterers and staff? ../lib/odp-util.c:5834:5: error: cast to smaller integer type 'unsigned long' from 'void *' [-Werror,-Wvoid-pointer-to-int-cast] I assumed that gcc makes a 65536 out of my define, but I was wrong. Again, all of the answers above missed the point badly. Thanks for contributing an answer to Stack Overflow! I am an entry level C programmer. SCAN_SINGLE("skb_priority(", uint32_t, u32, OVS_KEY_ATTR_PRIORITY); Yesterday, I updated Xcode to the newest version (5.1 (5B130a)) to compatible with iOS 7.1. That could create all kinds of trouble. Here is my code: I already tried (void*)M_TABLE_SIZE but then I get an error that I cannot use the * operator. Connect and share knowledge within a single location that is structured and easy to search. unsigned long call_fn = (unsigned long)FUNC; Asking for help, clarification, or responding to other answers. Any help with this is appreciated. ../lib/odp-util.c:5834:5: error: cast to smaller integer type 'unsigned long' from 'void *' [-Werror,-Wvoid-pointer-to-int-cast] Connect and share knowledge within a single location that is structured and easy to search. lexborisov Modest Public. Thanks for contributing an answer to Stack Overflow! then converted back to pointer to void, and the result will compare There's probably little you can do except look or hope for a fixed 2.x version or upgrade to 3.x (I would assume it's 64-bit safe but this is just a guess, do research this issue before you upgrade). You could use this code, and it would do the same thing as casting ptr to (char*). long guarantees a pointer size on Linux on any machine. This is why you got Error 1 C2036, from your post. "-I.." "-Iinclude\openflow" "-I..\include\openflow" "-Iinclude\openvswitch" "-I..\include\openvsw SCAN_PUT_ATTR(mask, ATTR, smask, FUNC); Thanks. Please tell me error: cast from 'void*' to 'int' loses precision, How Intuit democratizes AI development across teams through reusability. to the original pointer: The following type designates an unsigned integer type with the you can just change architecture to support 32 bit compilation by all below in in Build Settings. The high-order 9 bits of the number are used to hold a flag value, and the result is converted back into a pointer. Don't do that. You are right! How to tell which packages are held back due to phased updates, Identify those arcade games from a 1983 Brazilian music video. If you cast an int pointer int, you might get back a different integer. As Ferruccio said, int must be replaced with intptr_t to make the program meaningful. For example, the main thread could wait for all of the other threads to end before terminating. If the original pointer value represents an address of a byte in memory that does not satisfy the alignment requirement of the target type, then the resulting pointer value is unspecified. (i.e. What I am trying to do in that line of code is check to make sure each character in my string is alphabetical. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. 471,961 Members | 900 Online. Is a PhD visitor considered as a visiting scholar. (int*)Pc = pa; After the execution of the above code all the three pointers, i.e., Pa, Pd, and Pc, point to the value 150. If any, how can the original function works without errors if we just ignore the warning. If int is no larger than pointer to void then one way to store the value is by simply copying the bytes: int i . Bulk update symbol size units from mm to map units in rule-based symbology. 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. Does a summoned creature play immediately after being summoned by a ready action? Why did Ukraine abstain from the UNHRC vote on China? There is no "correct" way to store a 64-bit pointer in an 32-bit integer. Why is there a voltage on my HDMI and coaxial cables? Thanks Jonathan, I was thinking about my answer in another thread: AraK is correct, passing integers a pointers are not necessarily interchangeable. Is it possible to create a concave light? Maybe you can try this too. "After the incident", I started to be more careful not to trip over things. This page was last modified on 12 February 2023, at 18:25. LLNL's tutorial is bad and they should feel bad. Making statements based on opinion; back them up with references or personal experience. 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. The following behavior-changing defect reports were applied retroactively to previously published C++ standards. I have looked around and can't seem to find any information on how to do this. But assuming that it is, as long as the caller and the callee agree, you can do that sort of thing. As for the stack, I've written a few libraries using pthreds, thus I don't agree that what you describe "is quite often the case". Star 675. This will only compile if the destination type is long enough. return ((void **) returnPtr);} /* Matrix() */. For the remaining integral types, the result is the value of the enum if it can be represented by the target type and unspecified otherwise. Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. Converting a pointer to an integer whose result cannot represented in the integer type is undefined behavior is C and prohibited in C++. Do roots of these polynomials approach the negative of the Euler-Mascheroni constant? What happens if you typecast as unsigned first? There's no proper way to cast this to int in general case. Replacing broken pins/legs on a DIP IC package, AC Op-amp integrator with DC Gain Control in LTspice. See also this documentation.. From and Into are generally intended to be lossless, infalliable conversions.as on the other hand can discard data and lead to bugs in some situations, for example casting a u64 to a usize may truncate the value on a 32-bit host. It modifies >> Wconversion-real.c, Wconversion-real-integer.c and pr35635.c to be more >> specific > > If the patch passes existing tests, I'd be inclined to leave them > tests alone and add new ones that are specific to what this patch > changes. Casting arguments inside the function is a lot safer. Does Counterspell prevent from any further spells being cast on a given turn? Taking the above declarations of A, D, ch of the . So, when you cast a (void*) to (long), you are losing 32 bits of data in the conversion. To perform a cast, specify the type that you are casting to in parentheses in front of the value or variable to be converted. Windows has 32 bit long only on 64 bit as well. Therefore, you need to change it to long long instead of long in windows for 64 bits. A sane compiler may throw a warning on lines like this but by no way it should throw an error, because this code is NOT wrong, it is just potentially error-prone, but can be perfectly valid. Implementing From will result in the Into implementation but not vice-versa. Difficulties with estimation of epsilon-delta limit proof. Pull requests. Asking for help, clarification, or responding to other answers. I'm trying to create a void* from an int. Floating-point conversions Based on the design of this function, which modification is right. Please help me compile Chez Scheme. There exist two main syntaxes for generic type-casting: functional and c-like: 1 2 3 4 double x = 10.3; int y; y = int (x); // functional notation y = (int) x; // c-like cast notation The functionality of these generic forms of type-casting is enough for most needs with fundamental data types. The point is (probably) that the value passed to the thread is an integer value, not really a 'void *'. I recall there was a TreeNode(int) early on prior to 1.0 release I can't remember why I removed it, if I should felt it was easy enough to cast to (void*) or if it was because it created type inference conflict at the call site. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. But the problem has still happened. Fork 63. ), Styling contours by colour and by line thickness in QGIS. 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). A nit: in your version, the cast to void * is unnecessary. If you call your thread creation function like this, then the void* arriving inside of myFcn has the value of the int you put into it. But I don't want to edit code in "EAGLView.mm" because it's a "library file". It was derived from the BCPL, and the name of the b language is possibly from the BCPL contraction. Java Type Casting. So,solution #3 works just fine. Not the answer you're looking for? To learn more, see our tips on writing great answers. If you preorder a special airline meal (e.g. What you do here is undefined behavior, and undefined behavior of very practical sort. // OK: lvalue denoting the original d object, // UB: the b subobject is not a base class subobject, // 6. array-to-pointer followed by upcast, https://en.cppreference.com/mwiki/index.php?title=cpp/language/static_cast&oldid=147983, when converting a 'pointer to object' to 'pointer to, the conversion from floating-point values, the conversion from bit-fields to rvalue references, the conversion from integral or enumeration values to enumeration, the conversion from integral or enumeration values to, the conversion from a member of base class type to, a standard-layout class object with no data members, a non-standard-layout union object and a non-static data, for base-to-derived pointer conversions and, the conversion to enumeration types with fixed underlying type, a standard-layout class might have a non-pointer-interconvertible, If the underlying type is not fixed, the behavior is undefined if the value of, If the underlying type is fixed, the result is the same as, one is a union object and the other is a non-static data member of that object, or. error: comparison between pointer and integer ('int' and 'string' (aka 'char *')), CS50 Caesar program is working but check50 says it isn't. @kshegunov said in Number Type Cast: const void * x; int y = int (x); compiles just fine. Making statements based on opinion; back them up with references or personal experience. Please note that the error I am receiving is "cast to smaller integer type 'int' from 'string' (aka 'char *')" referencing line of code: while (isalpha (residents [i].name) == 0). SCAN_SINGLE("skb_priority(", uint32_t, u32, OVS_KEY_ATTR_PRIORITY); How do I align things in the following tabular environment? I agree passing a dynamically allocated pointer is fine (and I think the best way). You need to pass an actual pointer. Converting a void* to an int is non-portable way that may work or may not! In the case of Widening Type Casting, the lower data type (having smaller size) is converted into the higher data type (having larger size). Is it plausible for constructed languages to be used to affect thought and control or mold people towards desired outcomes? How do I set, clear, and toggle a single bit?