So, when you cast a (void*) to (long), you are losing 32 bits of data in the conversion. */void **MatrixIB (unsigned long x, unsigned long y, int size){ void *ptr; void **returnPtr; register unsigned long i, j; Api says this is how i should create thread: So if I want to pass an int what I think I should do is: The second example assumes that a pointer is wide enough to store an int. Do new devs get fired if they can't solve a certain bug? I have a two functions, one that returns an int, and one that takes a const void* as an argument. 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). How Intuit democratizes AI development across teams through reusability. Does melting sea ices rises global sea level? Replacing broken pins/legs on a DIP IC package, AC Op-amp integrator with DC Gain Control in LTspice. To learn more, see our tips on writing great answers. void* -> integer -> void* rather than integer -> void* -> integer. Find centralized, trusted content and collaborate around the technologies you use most. byte -> short -> char -> int -> long -> float -> double. In the first example, the variable c1 of the char type is converted to a temporary variable of the int type, because the second operand in the division operation, the constant 2, is of the higher type int. use $(ARCHS_STANDARD_32_BIT) at Architecture instead of $(ARCHS_STANDARD). What does it mean to convert int to void* or vice versa? 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. Netdev Archive on lore.kernel.org help / color / mirror / Atom feed * [mst-vhost:vhost 5/52] drivers/block/virtio_blk.c:539:21: warning: assignment to 'void *' from . Are there tables of wastage rates for different fruit and veg? ncdu: What's going on with this second size column? There's no proper way to cast this to int in general case. actually no, as int my be a smaller type than a pointer ;-) But, of course with int64_t it works fine. Notifications. ^~~~~~~~~~~~~~~~~~~~~ Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide. 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; rev2023.3.3.43278. BUT converting a pointer to void* and back again is well supported (everywhere). Using an integer address (like &x) is probably wrong, indeed each modification you will execute on x will affect the pass behaviour. @DietrichEpp can you explain what is race condition with using. return ((void **) returnPtr);} /* Matrix() */. If the original type is a void *, converting to an int may lose date on platforms where sizeof(void *) != sizeof(int) (which is true of LP64 programming model). 471,961 Members | 900 Online. whether it was an actual problem is a different matter though. If pointers are 64 bits and ints are 32 bits, an int is too small to hold a pointer value. The following program casts a double to an int. Casting an open pointer to other pointer types and casting other pointer types to an open pointer does not result in a compile time error. 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; even though the compiler doesn't know you only ever pass myFcn to pthread_create in conjunction with an integer. linux c-pthreads: problem with local variables. What does casting to void* does when passing arguments to variadic functions? 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). Why is this sentence from The Great Gatsby grammatical? It is easier to understand and write than any other assembly language. this question. I think the solution 3> should be the correct one. There is no "correct" way to store a 64-bit pointer in an 32-bit integer. rev2023.3.3.43278. What I am trying to do in that line of code is check to make sure each character in my string is alphabetical. Does Counterspell prevent from any further spells being cast on a given turn? How to get the error message from the error code returned by GetLastError()? 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 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. It solved my problem too. Not the answer you're looking for? How can this new ban on drag possibly be considered constitutional? That could create all kinds of trouble. Next, when doing pointer arithmetic, the addition operation will use the pointer's type to determine how many bytes to add to it when incrementing it. Floating-point conversions Connect and share knowledge within a single location that is structured and easy to search. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide, You should be doing int x = *((int *)arg); You are casting from void * to int that is why you get the warning. Passing arguments to pthread_create - invalid conversion from void(*)() to void(*)(void*). Unless you have a valid address at that value, you are going to invoke undefined behaviour when try to use that pointer. Where does this (supposedly) Gibson quote come from? This is a fine way to pass integers to new pthreads, if that is what you need. @Shahbaz you could but I will not suggest to a C newbie to use globals. This returns the first 32 bits of the pointer which may be the top or the bottom depending on big versus little endian, as comment #2 said. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. ../lib/odp-util.c:5658:9: note: expanded from macro 'SCAN_END_SINGLE' This will only compile if the destination type is long enough. He should pass the address of the integer, the thread should get that address, Note: This is only appropriate is you cast the. For example, the main thread could wait for all of the other threads to end before terminating. 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.. The program can be set in such a way to ask the user to inform the type of data and . Getting Command /bin/sh failed with exit code 65 Error with Xcode 5.1 . 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. 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. ../lib/odp-util.c:5665:7: note: expanded from macro 'SCAN_SINGLE' 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 is flat out wrong. Type casting is when you assign a value of one primitive data type to another type. Where does this (supposedly) Gibson quote come from? Thanks for contributing an answer to Stack Overflow! Staging Ground Beta 1 Recap, and Reviewers needed for Beta 2. 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. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. Well occasionally send you account related emails. C99 standard library provides intptr_t and uintptr_t typedefs, which are supposed to be used whenever the need to perform such a cast comes about. @LearnCocos2D: so, how can i "overcome" the error without editing any not-my-code or in-library-file lines? @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. But this code pass the normal variable .. The main point is: a pointer has a platform dependent size. However, I believe that even if the define was for the "65536", it would not be what @kaetzacoatl wanted. Thanks for pointing that out. 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). But assuming that it is, as long as the caller and the callee agree, you can do that sort of thing. what happens when we typecast normal variable to void* or any pointer variable? From what I read about casting in the C11 standard, my feeling is, that it is arguable to emit a warning on an explicit conversion. 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. */ >> -bool >> +enum conversion_safety >> unsafe_conversion_p (tree type, tree expr, bool . This is not a conversion at all. Infact I know several systems where that does not hold. What is the purpose of non-series Shimano components? Therefore, you need to change it to long long instead of long in windows for 64 bits. The pointer doesn't actually point to anything, but it's the result of an earlier cast from an integer to a pointer (e.g. Converts between types using a combination of implicit and user-defined conversions. A nit: in your version, the cast to void * is unnecessary. ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ you can just change architecture to support 32 bit compilation by all below in in Build Settings. How do I align things in the following tabular environment? It's an int type guaranteed to be big enough to contain a pointer. 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. Why do academics stay as adjuncts for years rather than move around? Therefore it is perfectly valid for the compiler to throw an error for a line like. Find centralized, trusted content and collaborate around the technologies you use most. How do I count the number of sentences in C using ". Only the following conversions can be done with static_cast, except when such conversions would cast away constness or volatility. static const void* M_OFFSET = (void*)64*1024; Since gcc compiles that you are performing arithmetic between void* and an int ( 1024 ). reinterpret_cast<void *>(42)). Connect and share knowledge within a single location that is structured and easy to search. This solution is in accordance with INT18-C. There's no proper way to cast this to int in general case. The proper way is to cast it to another pointer type. Visit Microsoft Q&A to post new questions. Offline ImPer Westermark over 11 years ago in reply to Andy Neil Except that you sometimes stores an integer in the pointer itself. Disconnect between goals and daily tasksIs it me, or the industry? Issues. And then assign it to the double variable. For a fairly recent compiler (that supports C99) you should not store or represent address as plain int value. Well it does this because you are converting a 64 bits pointer to an 32 bits integer so you loose information. Bulk update symbol size units from mm to map units in rule-based symbology. What is the point of Thrower's Bandolier? Already on GitHub? In 64-bit programs, the size of the pointer is 64 bits, and cannot be put into the int type, which remains 32-bit in almost all systems. But then you need to cast your arguments inside your thread function which is quite unsafe cf. I don't see how anything bad can happen . Acidity of alcohols and basicity of amines. To avoid truncating your pointer, cast it to a type of identical size. Using Kolmogorov complexity to measure difficulty of problems? SCAN_PUT(ATTR, NULL); Staging Ground Beta 1 Recap, and Reviewers needed for Beta 2. what does it mean to convert int to void* or vice versa? On most platforms pointers and longs are the same size, but ints and pointers often are not the same size on 64bit platforms. The subreddit for the C programming language, Press J to jump to the feed. 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. This forum has migrated to Microsoft Q&A. converted back to pointer to void, and the result will compare equal The result is implementation-defined and typically yields the numeric address of the byte in memory that the pointer pointers to. Put your define inside a bracket: without a problem. eg. (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. Thanks Jonathan, I was thinking about my answer in another thread: AraK is correct, passing integers a pointers are not necessarily interchangeable. Alternatively, if you choose to castthe ptr variableto (size_t) instead, then you don't need to worry about the pointer typeanymore. to the original pointer: The following type designates an unsigned integer type with the Connect and share knowledge within a single location that is structured and easy to search. 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. If the value is ever used as pointer again that will prove to be an extremely bad idea. Remarks. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. Since all pointers on 64-bit Windows are 64 bits, you are growing the data size from 32 bits backto 64 bits. Just edited. Asking for help, clarification, or responding to other answers. This allows you to reinterpret the void * as an int. I would create a structure and pass that as void* to pthread_create. 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. 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. I have a function with prototype void* myFcn(void* arg) which is used as the starting point for a pthread. Losing bytes like thisis called 'truncation', and that's what the first warning is telling you. ^~~~~~~~~~~~~~~~~~~~~ . Thanks for contributing an answer to Stack Overflow! Remembering to delete the pointer after use so that we don't leak. Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide, "what happen when typcating normal variable to void* or any pointer variable?" Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide. 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; The only alternative is really to take time and fix all 64-bit code issues, of which there may be some non-trivial issues. I cannot reverse my upvote of user384706's answer, but it's wrong. This page was last modified on 12 February 2023, at 18:25. Does a summoned creature play immediately after being summoned by a ready action? Windows has 32 bit long only on 64 bit as well. What is the purpose of non-series Shimano components? C/C++ , Cerror: cast to 'void *' from smaller integer type 'int'. Create an account to follow your favorite communities and start taking part in conversations. reinterpret_cast is a type of casting operator used in C++. Using indicator constraint with two variables. B language was designed to develop . So, when you cast a (void*) to (long), you are losing 32 bits of data in the conversion. To learn more, see our tips on writing great answers. How to correctly cast a pointer to int in a 64-bit application? However even though their types are different, the address is going to be the same. Don't do that. The problem just occur with Xcode 5.1. My code is GPL licensed, can I issue a license to have my code be distributed in a specific MIT licensed project? ^~~~~~~~~~~~~~~~~~~~ Now, what happens when I run it with the thread sanitizer? If this is the data to a thread procedure, then you quite commonly want to pass by value. So you know you can cast it back like this. This is memory reinterpretation - a completely unacceptable way to do what the OP is trying to do. To learn more, see our tips on writing great answers. Your first example is risky because you have to be very careful about the object lifetimes. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. ), Styling contours by colour and by line thickness in QGIS. Do roots of these polynomials approach the negative of the Euler-Mascheroni constant? Error while setting app icon and launch image in xcode 5.1. "I think what you should do is actually pass the address of the variable to the function" Not necessarily. How do I set, clear, and toggle a single bit? 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)). Making statements based on opinion; back them up with references or personal experience. And you can't pass a pointer to a stack based object from the other thread as it may no longer be valid. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. From that point on, you are dealing with 32 bits. I usually have all automatic conversion warnings effective when developing in C, and I use explicit casting in order to suppress a specific . Is it possible to create a concave light? You can only do this if you use a synchronization primitive to ensure that there is no race condition. I'm trying to learn pthreads and thing that keeps bugging me is how do i really pass argument to the function. Typically, long or unsigned long is . casting from int to void* and back to int. Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide, @Dinesh: could you please 1) show us those. The point is (probably) that the value passed to the thread is an integer value, not really a 'void *'. Press question mark to learn the rest of the keyboard shortcuts. rev2023.3.3.43278. 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). Mutually exclusive execution using std::atomic? Update: Today, i download the latest version of cocos2d-x (cocos2d-x 2.2.3). 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 vegan) just to try it, does this inconvenience the caterers and staff? 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;. I agree passing a dynamically allocated pointer is fine (and I think the best way). And in this context, it is very very very common to see programmers lazily type cast the. A void pointer can be really useful if the programmer is not sure about the data type of data inputted by the end user. Java Type Casting. Converting one datatype into another is known as type casting or, type-conversion. Do roots of these polynomials approach the negative of the Euler-Mascheroni constant? How to convert a factor to integer\numeric without loss of information? Making statements based on opinion; back them up with references or personal experience. A cast is a way of explicitly informing the compiler that you intend to make the conversion and that you are aware that data loss might occur, or the cast may fail at run time. 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. How to use Slater Type Orbitals as a basis functions in matrix method correctly? 10) A prvalue of type pointer to void (possibly cv-qualified) can be converted to pointer to any object type. Example: int x=7, y=5; float z; z=x/y; /*Here the value of z is 1*/. Such a downcast makes no runtime checks to ensure that the object's runtime type is actually D, and may only be used safely if this precondition is guaranteed by other means, such as when implementing static polymorphism. 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. You may declare a const int variable and cast its reference to the void*. a cast of which the programmer should be aware of what (s)he is doing. Then i can continue compiling. Evaluate integer expressions in a larger size before comparing or assigning to that size.Note that (time_+t)-1 also complies with INT31-C-EX3. If the object expression refers or points to is actually a base class subobject of an object of type D, the result refers to the enclosing object of type D. Otherwise, the behavior is undefined: When the target type is bool (possibly cv-qualified), the result is false if the original value is zero and true for all other values. The int data type is the primary integer data type in SQL Server. This is what the second warning is telling you. and how to print the thread id of 2d array argument? Thanks. Share Improve this answer Follow answered May 6, 2018 at 7:24 Rahul A cast converts an object or value from one type to another. : iPhone Retina 4-inch 64-bit) is selected. (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. The difference between the phonemes /p/ and /b/ in Japanese. The cast back to int * is not, though. An open (void) pointer can hold a pointer of any type. If you preorder a special airline meal (e.g. As was pointed out by Martin, this presumes that sizeof(void*)>=sizeof(int). cast operators [edit] When an expression is used in the context where a value of a different type is expected, conversionmay occur: intn =1L;// expression 1L has type long, int is expectedn =2.1;// expression 2.1 has type double, int is expectedchar*p =malloc(10);// expression malloc(10) has type void*, char* is expected But, sure, in that specific case you can pass a local variable address, type casting integer to void* [duplicate]. Not the answer you're looking for? If the value in a pointer is cast to a different type and it does not have the correct alignment for the new type, the behavior is undefined. A missing cast in the new fast > enumeration code. This is known as implicit type casting or type promotion, compiler automatically converts smaller data type to larger data type. If any, how can the original function works without errors if we just ignore the warning. In C (int)b is called an explicit conversion, i.e. I get the error: "cast to smaller integer type 'int' from 'string' (aka 'char *')" referencing line of code: while (isalpha(residents[i].name) == 0), How Intuit democratizes AI development across teams through reusability. Please help me compile Chez Scheme. My code is all over the place now but I appreciate you all helping me on my journey to mastery! Difficulties with estimation of epsilon-delta limit proof. (int) pthread_self() 64int48intuintptr_t (unsigned int) lexborisov Modest Public. I'm new to coding and am trying to implement a simple program on my own, that prompts the user the number of residents in an apt complex, the prompts the user to enter the names and apt numbers of each resident. @DavidHeffernan I rephrased that sentence a little. Mutually exclusive execution using std::atomic? rev2023.3.3.43278. Did any DOS compatibility layers exist for any UNIX-like systems before DOS started to become outmoded? You are correct, but cocos actually only uses that address as a unique id. You could use this code, and it would do the same thing as casting ptr to (char*). C99 standard library provides intptr_t and uintptr_t typedefs, which are supposed to be used whenever the need to perform such a cast comes about. The preprocesor absolutely will not perform arithmetic. The result is the same as implicit conversion from the enum's underlying type to the destination type. So,solution #3 works just fine. What Is the Difference Between 'Man' And 'Son of Man' in Num 23:19? ../lib/odp-util.c:5665:7: note: expanded from macro 'SCAN_SINGLE' This is an old C callback mechanism so you can't change that.
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