Connect and share knowledge within a single location that is structured and easy to search. However, you are also casting the result of this operation to (void*). My code is GPL licensed, can I issue a license to have my code be distributed in a specific MIT licensed project? Projects. If your code has the chance to ever be ported to some platform where this doesn't hold, this won't work. ../lib/odp-util.c:5658:9: note: expanded from macro 'SCAN_END_SINGLE' Making statements based on opinion; back them up with references or personal experience. Get the address of a callback function to call dynamically in C++, error: call of overloaded function ambiguous, error: cast from to unsigned int loses precision [-fpermissive]. 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. 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. Bulk update symbol size units from mm to map units in rule-based symbology. All character types are to be converted to an integer. From that point on, you are dealing with 32 bits. Can anybody explain how to pass an integer to a function which receives (void * ) as a parameter? Using Kolmogorov complexity to measure difficulty of problems? Since gcc compiles that you are performing arithmetic between void* and an int (1024). /** Dynamically allocate a 2d (x*y) array of elements of size _size_ bytes. To learn more, see our tips on writing great answers. Yeah, the tutorial is doing it wrong. Where does this (supposedly) Gibson quote come from? Usually that means the pointer is allocated with. ", "? To subscribe to this RSS feed, copy and paste this URL into your RSS reader. But I don't want to edit code in "EAGLView.mm" because it's a "library file". 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. static const void* M_OFFSET = (void*)64*1024; Since gcc compiles that you are performing arithmetic between void* and an int ( 1024 ). You cannot just cast the 32-bit variable to a pointer, because that pointer on a 64-bit machine is twice as long. Converts between types using a combination of implicit and user-defined conversions. STR34-C. 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. Typically, long or unsigned long is . There is no "correct" way to store a 64-bit pointer in an 32-bit integer. 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. 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; privacy statement. I think the solution 3> should be the correct one. Once you manage to make this cast, then what?! 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. Based on the design of this function, which modification is right. If you really need such trickery, then consider one of dedicated types, which are intptr_t and uintptr_t. Making statements based on opinion; back them up with references or personal experience. Mutually exclusive execution using std::atomic? 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. That could create all kinds of trouble. How do I check if a string represents a number (float or 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;. error: comparison between pointer and integer ('int' and 'string' (aka 'char *')), CS50 Caesar program is working but check50 says it isn't. Staging Ground Beta 1 Recap, and Reviewers needed for Beta 2. 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). In such a case the programmer can use a void pointer to point to the location of the unknown data type. Is it plausible for constructed languages to be used to affect thought and control or mold people towards desired outcomes? When is casting void pointer needed in C? What is the point of Thrower's Bandolier? vegan) just to try it, does this inconvenience the caterers and staff? That's not a good idea if the original object (that was cast to void*) was an integer. Euler: A baby on his lap, a cat on his back thats how he wrote his immortal works (origin?). 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. 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 idea how it amassed 27 upvotes?! how to cascade 2d int array to 2d void pointer array? Only the following conversions can be done with static_cast, except when such conversions would cast away constness or volatility. ^~~~~~~~~~~~~~~~~~~~~ Whats the grammar of "For those whose stories they are"? (i.e. Then i can continue compiling. ), Styling contours by colour and by line thickness in QGIS. (int) pthread_self() 64int48intuintptr_t (unsigned int) How do I set, clear, and toggle a single bit? What does it mean to convert int to void* or vice versa? Before I update Xcode, my project still can build and run normally with all devices. The subreddit for the C programming language, Press J to jump to the feed. Notifications. Connect and share knowledge within a single location that is structured and easy to search. ), For those who are interested. 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. In Java, there are two types of casting: Widening Casting (automatically) - converting a smaller type to a larger type size. Remembering to delete the pointer after use so that we don't leak. 1. Whats the grammar of "For those whose stories they are"? A pointer converted to an integer of sufficient size and back to the same pointer type is guaranteed to have its original value, otherwise the resulting pointer cannot be dereferenced safely ( the round-trip conversion in the opposite direction is not guaranteed [.]) All float types are to be converted to double. 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. AC Op-amp integrator with DC Gain Control in LTspice. @DavidHeffernan, sane thread APIs wouldn't send integral data to the thread procedures, they would send pointers. How to use Slater Type Orbitals as a basis functions in matrix method correctly? Asking for help, clarification, or responding to other answers. 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. In both cases, converting the pointer to an integer type that's too small to represent all pointer values is a bug. Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. Example: int x=7, y=5; float z; z=x/y; /*Here the value of z is 1*/. 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. So you know you can cast it back like this. void* -> integer -> void* rather than integer -> void* -> integer. However the actual code in question contains an explicit c-style cast to int. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide. Since all pointers on 64-bit Windows are 64 bits, you are growing the data size from 32 bits backto 64 bits. @BlueMoon Thanks a lot! 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. The result is the same as implicit conversion from the enum's underlying type to the destination type. Is a PhD visitor considered as a visiting scholar. "clang" "-Ilib\libopenvswitch.a.p" "-Ilib" "-I..\lib" "-I." "because the type "int" supports only -32768 ~ 32768" This is not true for any modern desktop or mobile OS or any OS that is targeted by cocos2d-x. Is it suspicious or odd to stand by the gate of a GA airport watching the planes? Thanks for pointing that out. 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; If you preorder a special airline meal (e.g. @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. However, I believe that even if the define was for the "65536", it would not be what @kaetzacoatl wanted. If the value is ever used as pointer again that will prove to be an extremely bad idea. I guess the other important fact is that the cast operator has higher precedence that the multiplication operator. C / C++ Forums on Bytes. Why do small African island nations perform better than African continental nations, considering democracy and human development? Do roots of these polynomials approach the negative of the Euler-Mascheroni constant? The difference between the phonemes /p/ and /b/ in Japanese. For example, the main thread could wait for all of the other threads to end before terminating. On a 64-bit Windows computer, 'long' is a 32-bit type, and all pointers are 64-bit types. Replacing broken pins/legs on a DIP IC package, AC Op-amp integrator with DC Gain Control in LTspice. I wish that you write those answer first than the explanation. There's no proper way to cast this to int in general case. Alternatively, if you choose to castthe ptr variableto (size_t) instead, then you don't need to worry about the pointer typeanymore. This page has been accessed 1,655,678 times. ../lib/odp-util.c:5601:9: note: expanded from macro 'SCAN_PUT' Difficulties with estimation of epsilon-delta limit proof. To learn more, see our tips on writing great answers. ncdu: What's going on with this second size column? How do I force make/GCC to show me the commands? Not the answer you're looking for? Connect and share knowledge within a single location that is structured and easy to search. Does melting sea ices rises global sea level? Making statements based on opinion; back them up with references or personal experience. Otherwise, if the original pointer value points to an object a, and there is an object b of the . Noncompliant Code Example (memset())For historical reasons, certain C Standard functions accept an argument of type int and convert it to either unsigned char or plain char. Is it possible to create a concave light? A cast specifies a conversion from one type to another. Do roots of these polynomials approach the negative of the Euler-Mascheroni constant? 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. 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. actually no, as int my be a smaller type than a pointer ;-) But, of course with int64_t it works fine. I usually have all automatic conversion warnings effective when developing in C, and I use explicit casting in order to suppress a specific . what does it mean to convert int to void* or vice versa? This is known as implicit type casting or type promotion, compiler automatically converts smaller data type to larger data type. Mutually exclusive execution using std::atomic? Please unaccept the answer you have chosen as it is wrong (as the comments below it say) and will lead to bugs. However even though their types are different, the address is going to be the same. How do I work around the GCC "error: cast from SourceLocation* to int loses precision" error when compiling cmockery.c? A nit: in your version, the cast to void * is unnecessary. Staging Ground Beta 1 Recap, and Reviewers needed for Beta 2, Setting a buffer of char* with intermediate casting to int*. The int data type is the primary integer data type in SQL Server. 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. What can a lawyer do if the client wants him to be acquitted of everything despite serious evidence? How create a simple program using threads in C? But I'm nitpicking .. Asking for help, clarification, or responding to other answers. Therefore, you need to change it to long long instead of long in windows for 64 bits. It's an int type guaranteed to be big enough to contain a pointer. FAILED: lib/libopenvswitch.a.p/odp-util.c.obj You are right! SCAN_PUT_ATTR(key, ATTR, skey, FUNC); How do I align things in the following tabular environment? 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. SCAN_PUT_ATTR(mask, ATTR, smask, FUNC); ../lib/odp-util.c:5834:5: error: cast to smaller integer type 'unsigned long' from 'void *' [-Werror,-Wvoid-pointer-to-int-cast] warning C4311: 'type cast': pointer truncation from 'void *' to 'long' in ECPG test files. The only alternative is really to take time and fix all 64-bit code issues, of which there may be some non-trivial issues. Instead of using a long cast, you should cast to size_t. (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. rev2023.3.3.43278. linux c-pthreads: problem with local variables. Why is there a voltage on my HDMI and coaxial cables? By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. 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. If you preorder a special airline meal (e.g. Please tell me error: cast from 'void*' to 'int' loses precision, How Intuit democratizes AI development across teams through reusability. Thanks for contributing an answer to Stack Overflow! Implementation-dependent. ../lib/odp-util.c:5665:7: note: expanded from macro 'SCAN_SINGLE' rev2023.3.3.43278. Where does this (supposedly) Gibson quote come from? Disconnect between goals and daily tasksIs it me, or the industry? If you cast an int pointer int, you might get back a different integer. This page was last modified on 12 February 2023, at 18:25. Offline ImPer Westermark over 11 years ago in reply to Andy Neil Except that you sometimes stores an integer in the pointer itself. Bulk update symbol size units from mm to map units in rule-based symbology. Thanks for contributing an answer to Stack Overflow! Taking the above declarations of A, D, ch of the . You are getting warnings due to casting a void* to a type of a different size. : iPhone Retina 4-inch 64-bit) is selected. @Martin York: No, it doesn't depend on endiannness. The following behavior-changing defect reports were applied retroactively to previously published C++ standards. There are ways to prevent this: pass a dynamic allocated argument if your not the passing thread is not static or if your argument is a local variable, otherwise there is no issue. In the case of Widening Type Casting, the lower data type (having smaller size) is converted into the higher data type (having larger size). I have a two functions, one that returns an int, and one that takes a const void* as an argument. So,solution #3 works just fine. LLNL's tutorial is bad and they should feel bad. Why are Suriname, Belize, and Guinea-Bissau classified as "Small Island Developing States"? Thanks for contributing an answer to Stack Overflow! Terrible solution. Are there tables of wastage rates for different fruit and veg? So, when you cast a (void*) to (long), you are losing 32 bits of data in the conversion. Issues. Using an integer address (like &x) is probably wrong, indeed each modification you will execute on x will affect the pass behaviour. converted back to pointer to void, and the result will compare equal Sign up for a free GitHub account to open an issue and contact its maintainers and the community. The correct answer is, if one does not mind losing data precision. What Is the Difference Between 'Man' And 'Son of Man' in Num 23:19? 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. Therefore it is perfectly valid for the compiler to throw an error for a line like. If the destination type is bool, this is a boolean conversion (see below). A void pointer can be really useful if the programmer is not sure about the data type of data inputted by the end user. 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. to the original pointer: The following type designates an unsigned integer type with the */void **MatrixIB (unsigned long x, unsigned long y, int size){ void *ptr; void **returnPtr; register unsigned long i, j; returnPtr = (void **) malloc (x * sizeof(void *)); ptr = (void *) malloc (x * y * size); for (i=0, j=0; j returnPtr[j] = (void *) (ptr + i); // <<< Compile Errors, Error1error C2036: 'void *' : unknown sizec:\temp\testone\lib\utils.c57, 2> returnPtr[j] = (void *) ((long*)ptr + i); // <<< No compile errors, 3> returnPtr[j] = (void *) ((char*)ptr + i); // <<< No compile errors. B programing language is a language based on basic combined programming or a BCPL, and it is the precursor of the C programming language. Asking for help, clarification, or responding to other answers. and how to print the thread id of 2d array argument? To avoid truncating your pointer, cast it to a type of identical size. To learn more, see our tips on writing great answers. If you write ((char*)ptr + 1), it will advance the pointer 1 byte, because a "char" is 1 byte. If pointers are 64 bits and ints are 32 bits, an int is too small to hold a pointer value. p-util.c.obj "-c" ../lib/odp-util.c And then assign it to the double variable. Functions return bigint only if the parameter expression is a bigint data type. If you are planning to use pthreads and you are planning to pass the pass function to pthread_create, you have to malloc/free the arguments you are planning to use (even if the threaded function just need a single int). Is it plausible for constructed languages to be used to affect thought and control or mold people towards desired outcomes? Share Improve this answer Follow answered May 6, 2018 at 7:24 Rahul This is a fine way to pass integers to new pthreads, if that is what you need. for (i=0, j=0; j Love's Executioner Two Smiles Summary, Articles C