However the actual code in question contains an explicit c-style cast to int. I usually have all automatic conversion warnings effective when developing in C, and I use explicit casting in order to suppress a specific . Why does flowing off the end of a non-void function without returning a value not produce a compiler error? SCAN_PUT_ATTR(mask, ATTR, smask, FUNC); 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. Well it does this because you are converting a 64 bits pointer to an 32 bits integer so you loose information. You can use a 64 bits integer instead howerver I usually use a function with the right prototype and I cast the function type : 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. Connect and share knowledge within a single location that is structured and easy to search. Use returnPtr[j] = (void *) ((long)ptr + i); ). On a 64-bit Windows computer, 'long' is a 32-bit type, and all pointers are 64-bit types. However, you are also casting the result of this operation to (void*). 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. Remarks. The high-order 9 bits of the number are used to hold a flag value, and the result is converted back into a pointer. What does it mean to convert int to void* or vice versa? 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. How to use Slater Type Orbitals as a basis functions in matrix method correctly? Thanks for contributing an answer to Stack Overflow! returnPtr = (void **) malloc (x * sizeof(void *)); ptr = (void *) malloc (x * y * size); Put your define inside a bracket: without a problem. Floating-point conversions Sign up for a free GitHub account to open an issue and contact its maintainers and the community. This example is noncompliant on an implementation where pointers are 64 bits and unsigned integers are 32 bits because the result of converting the 64-bit ptr cannot be represented in the 32-bit integer type. 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". But you seem to suggest by your answer that the user can pass 5 to pthread_create and then perform the above cast to get it back. (i.e. Disconnect between goals and daily tasksIs it me, or the industry? How Intuit democratizes AI development across teams through reusability. The only alternative is really to take time and fix all 64-bit code issues, of which there may be some non-trivial issues. privacy statement. Just re-enforcing the old behavior of Xcode 5.0 and earlier versions, that already cut away parts of the address by casting it to int, won't introduce any new bugs and avoids the need to learn and understand lots of implementation-internal cocos code. From the question I presume the OP does. If int is no larger than pointer to void then one way to store the value is by simply copying the bytes: int i . Now, what happens when I run it with the thread sanitizer? A cast specifies a conversion from one type to another. The result is the same as implicit conversion from the enum's underlying type to the destination type. 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). 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. Since the 'size' argument for your function is the number of bytes each element in the array needs, I think casting the pointerto (char*) is appropriate. As a result of the integer division 3/2 we get the value 1, which is of the int type. Implementation-dependent. Thanks for contributing an answer to Stack Overflow! I wish that you write those answer first than the explanation. If you do this, you have the thread reference a value that (hopefully still) lives in some other thread. C / C++ Forums on Bytes. Thanks for contributing an answer to Stack Overflow! ), For those who are interested. By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. The subreddit for the C programming language, Press J to jump to the feed. 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. The text was updated successfully, but these errors were encountered: ", "!"? Using Kolmogorov complexity to measure difficulty of problems? 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. Did any DOS compatibility layers exist for any UNIX-like systems before DOS started to become outmoded? Cast characters to unsigned char before converting to larger integer sizes Created by Robert Seacord, last modified by Jill Britton on Oct 03, 2022 Signed character data must be converted to unsigned char before being assigned or converted to a larger signed type. GitHub. } SCAN_END_SINGLE(ATTR) The calculated expression consists of two operations. My code is GPL licensed, can I issue a license to have my code be distributed in a specific MIT licensed project? 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. The cast back to int * is not, though. Maybe you can try this too. I guess the other important fact is that the cast operator has higher precedence that the multiplication operator. 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. Note the difference between the type casting of a variable and type casting of a pointer. Making statements based on opinion; back them up with references or personal experience. this way you won't get any warning. How to correctly cast a pointer to int in a 64-bit application? What is the correct method to cast an int to a void*? (int) pthread_self() 64int48intuintptr_t (unsigned int) Is it plausible for constructed languages to be used to affect thought and control or mold people towards desired outcomes? . Not the answer you're looking for? All float types are to be converted to double. Using indicator constraint with two variables. By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. 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. Why is this sentence from The Great Gatsby grammatical? rev2023.3.3.43278. 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). [] ExplanatioUnlike static_cast, but like const_cast, the reinterpret_cast expression does not compile to any CPU instructions (except when converting between integers and pointers or on obscure architectures where pointer representation depends on its type). You could use this code, and it would do the same thing as casting ptr to (char*). You should perform type conversion based on 64bit build system because the type "int" supports only -32768 ~ 32768. 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. Changing the type of ids would be the cleanest solution, but I decided against it when being confronted with this issue myself, as it only introduced a lot of issues with other code that is relying on ids being an int-array. rev2023.3.3.43278. Implementing From will result in the Into implementation but not vice-versa. 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. Thank you all for your feedback. Casting int to void* loses precision, and what is the solution in required cases, c++: cast from "const variable*" to "uint32" loses precision, Recovering from a blunder I made while emailing a professor, Relation between transaction data and transaction id. 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 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. @DavidHeffernan I rephrased that sentence a little. ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ and how to print the thread id of 2d array argument? 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 Connect and share knowledge within a single location that is structured and easy to search. What I am trying to do in that line of code is check to make sure each character in my string is alphabetical. Don't do that. Once you manage to make this cast, then what?! ^~~~~~~~~~~~~~~~~~~~ Casting arguments inside the function is a lot safer. The value of float variable is= 37.75. Is a PhD visitor considered as a visiting scholar. To perform a cast, specify the type that you are casting to in parentheses in front of the value or variable to be converted. ^~~~~~~~~~~~~~~~~~~ The correct answer is, if one does not mind losing data precision. You are correct, but cocos actually only uses that address as a unique id. - the incident has nothing to do with me; can I use this this way? "-I.." "-Iinclude\openflow" "-I..\include\openflow" "-Iinclude\openvswitch" "-I..\include\openvsw This page was last modified on 12 February 2023, at 18:25. My code is all over the place now but I appreciate you all helping me on my journey to mastery! *sound/soc/codecs/tlv320aic32x4.c:1202:18: warning: cast to smaller integer type 'enum aic32x4_type' from 'void *' @ 2022-04-22 9:48 kernel test robot 0 siblings, 0 . Whats the grammar of "For those whose stories they are"? Please tell me error: cast from 'void*' to 'int' loses precision, How Intuit democratizes AI development across teams through reusability. I'm trying to learn pthreads and thing that keeps bugging me is how do i really pass argument to the function. If you convert (void*) to (long) no precision is lost, then by assigning the (long) to an (int), it properly truncates the number to fit. windows meson: cast to smaller integer type 'unsigned long' from 'void *'. B programing language is a language based on basic combined programming or a BCPL, and it is the precursor of the C programming language. this way you won't get any warning. Making statements based on opinion; back them up with references or personal experience. 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. To access the object value, use the * dereference operator: int * p; assert (p == null ); p = new int (5); assert (p != null ); assert (*p == 5); (*p)++; assert (*p == 6); If a pointer contains a null value, it is not pointing to a valid object. 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. Why do small African island nations perform better than African continental nations, considering democracy and human development? What I am trying to do in that line of code is check to make sure each character in my string is alphabetical. This will only compile if the destination type is long enough. 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; By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. There is absolutely not gurantee that sizeof(int) <= sizeof(void*). [that could be a TODO - not to delay solving the ICE]. 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. Why does Mister Mxyzptlk need to have a weakness in the comics? And in this context, it is very very very common to see programmers lazily type cast the. p-util.c.obj "-c" ../lib/odp-util.c What you do here is undefined behavior, and undefined behavior of very practical sort. Based on the design of this function, which modification is right. Such pointers can be stored in 32-bit data types (for instance, int, DWORD). Making statements based on opinion; back them up with references or personal experience. Don't do that. ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ To avoid truncating your pointer, cast it to a type of identical size. XCode 5.1 is change all architecture to 64 bit. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide. ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~. Are there tables of wastage rates for different fruit and veg? (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. linux c-pthreads: problem with local variables. How do I work around the GCC "error: cast from SourceLocation* to int loses precision" error when compiling cmockery.c? How do I set, clear, and toggle a single bit? What does casting to void* does when passing arguments to variadic functions? What is the point of Thrower's Bandolier? Not the answer you're looking for? Mutually exclusive execution using std::atomic? -1, Uggh. 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. This is not even remotely "the correct answer". Find centralized, trusted content and collaborate around the technologies you use most. Terrible solution. 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). Star 675. 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. You need to cast the void* pointer to a char* pointer - and then dereference that char* pointer to give you the char that it points to! 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. static_cast on the other hand should deny your stripping away the const qualifier. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. This forum has migrated to Microsoft Q&A. Most answers just try to extract 32 useless bits out of the argument. SCAN_SINGLE("skb_priority(", uint32_t, u32, OVS_KEY_ATTR_PRIORITY); "clang" "-Ilib\libopenvswitch.a.p" "-Ilib" "-I..\lib" "-I." 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. 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. This is known as implicit type casting or type promotion, compiler automatically converts smaller data type to larger data type. 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. @Martin York: No, it doesn't depend on endiannness. 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)). Click to see the query in the CodeQL repository. Note:You might receive a runtime exception if the pointer contains a value unsuitable for the context. (void *)i Error: cast to 'void *' from smaller integer type 'int' PS: UBUNTUCLANG3.5 clang -O0 -std=gnu11 -march=native -lm -lpthread pagerank.c -o pagerank c pthreads 4 10.3k 2 21 2015-06-05 On most platforms pointers and longs are the same size, but ints and pointers often are not the same size on 64bit platforms. Mutually exclusive execution using std::atomic? @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. By clicking Sign up for GitHub, you agree to our terms of service and That could create all kinds of trouble. Taking the above declarations of A, D, ch of the . Already on GitHub? If you write ((char*)ptr + 1), it will advance the pointer 1 byte, because a "char" is 1 byte. actually no, as int my be a smaller type than a pointer ;-) But, of course with int64_t it works fine. @Shahbaz you could but I will not suggest to a C newbie to use globals. What Is the Difference Between 'Man' And 'Son of Man' in Num 23:19? That's not a good idea if the original object (that was cast to void*) was an integer. Does Counterspell prevent from any further spells being cast on a given turn? If you really need such trickery, then consider one of dedicated types, which are intptr_t and uintptr_t. This is why you got Error 1 C2036, from your post. If your standard library (even if it is not C99) happens to provide these types - use them. Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. Bulk update symbol size units from mm to map units in rule-based symbology. This allows you to reinterpret the void * as an int. C++ how to get the address stored in a void pointer? 471,961 Members | 900 Online. Find centralized, trusted content and collaborate around the technologies you use most. Staging Ground Beta 1 Recap, and Reviewers needed for Beta 2. ncdu: What's going on with this second size column? This will get you a pointer from a 32 bit offset: A function pointer is incompatible to void* (and any other non function pointer). Properly casting a `void*` to an integer in C++ 24,193 Solution 1 I think using intptr_t is the correct intermediate here, since it's guaranteed to be large enough to contain the integral value of the void*, and once I have an integer value I can then truncate it without causing the compiler to complain. Is pthread_join a must when using pthread in linux? x is a local variable and its lifetime ends as soon as control leaves the scope it was defined in. The preprocesor absolutely will not perform arithmetic. 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. What is the difference between const int*, const int * const, and int const *? What I am trying to emphasis that conversion from int to pointer and back again can be frough with problems as you move from platform to platform. ", "? Can I tell police to wait and call a lawyer when served with a search warrant? Pull requests. If the destination type is bool, this is a boolean conversion (see below). Half your pointer will be garbage. The most general answer is - in no way. Narrowing Casting (manually) - converting a larger type to a . How do I force make/GCC to show me the commands? 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. 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. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. Typically, long or unsigned long is . If not, check the pointer size on your platform, define these typedefs accordingly yourself and use them. I'm using cocos2d-x-2.2.2. No idea how it amassed 27 upvotes?! Whats the grammar of "For those whose stories they are"? So make sure you understand what you are doing! I would create a structure and pass that as void* to pthread_create. In a 64bit build a pointer is 64bit (contrary to a 32bit build, where it is 32bit), while an int is 32bit, so this assignment stores a 64bit value in a 32bit storage, which may result in a loss of information. C/C++ , Cerror: cast to 'void *' from smaller integer type 'int'. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide. A nit: in your version, the cast to void * is unnecessary. An object pointer (including void*) or function pointer can be converted to an integer type using reinterpret_cast. Therefore, you need to change it to long long instead of long in windows for 64 bits. Staging Ground Beta 1 Recap, and Reviewers needed for Beta 2, Setting a buffer of char* with intermediate casting to int*. I have a function with prototype void* myFcn(void* arg) which is used as the starting point for a pthread. ncdu: What's going on with this second size column? To subscribe to this RSS feed, copy and paste this URL into your RSS reader. Where does this (supposedly) Gibson quote come from? 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. Mutually exclusive execution using std::atomic? @BlueMoon Thanks a lot! How create a simple program using threads in C? Find centralized, trusted content and collaborate around the technologies you use most. In such a case the programmer can use a void pointer to point to the location of the unknown data type. 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. 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]. This is memory reinterpretation - a completely unacceptable way to do what the OP is trying to do. So,solution #3 works just fine. ../lib/odp-util.c:5658:9: note: expanded from macro 'SCAN_END_SINGLE' Asking for help, clarification, or responding to other answers. Unless you have a valid address at that value, you are going to invoke undefined behaviour when try to use that pointer. Using an integer address (like &x) is probably wrong, indeed each modification you will execute on x will affect the pass behaviour. Notifications. Connect and share knowledge within a single location that is structured and easy to search. @DavidHeffernan, sane thread APIs wouldn't send integral data to the thread procedures, they would send pointers. // 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. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. If this is the data to a thread procedure, then you quite commonly want to pass by value. lexborisov Modest Public. C99 defines the types "intptr_t" and "uintptr_t" which do . this way I convert an int to a void* which is much better than converting a void* to an int. 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. What can a lawyer do if the client wants him to be acquitted of everything despite serious evidence? 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.. What Is the Difference Between 'Man' And 'Son of Man' in Num 23:19? How to use Slater Type Orbitals as a basis functions in matrix method correctly? SCAN_SINGLE("skb_priority(", uint32_t, u32, OVS_KEY_ATTR_PRIORITY); This solution is in accordance with INT18-C. casting from int to void* and back to int. As Ferruccio said, int must be replaced with intptr_t to make the program meaningful. Using Kolmogorov complexity to measure difficulty of problems? SCAN_PUT(ATTR, NULL); 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). The only exception is exotic systems with the SILP64 data model, where the size of int is also 64 bits. STR34-C. You may declare a const int variable and cast its reference to the void*. I am an entry level C programmer. Why is there a voltage on my HDMI and coaxial cables? Therefore it is perfectly valid for the compiler to throw an error for a line like. Please unaccept the answer you have chosen as it is wrong (as the comments below it say) and will lead to bugs. rev2023.3.3.43278. Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. The proper way is to cast it to another pointer type. This page has been accessed 1,655,678 times. Hence there is no loss in data. How do I check if a string represents a number (float or int)? The difference between the phonemes /p/ and /b/ in Japanese. I need to cast the int from the first function so that I can use it as an argument for the second function. 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 . Then i can continue compiling. Staging Ground Beta 1 Recap, and Reviewers needed for Beta 2. what does it mean to convert int to void* or vice versa? If you need to keep the returned address, just keep it as void*. The program can be set in such a way to ask the user to inform the type of data and . If you preorder a special airline meal (e.g. No sense in writing a few dozen lines of extra code just to get a bunch of numbered threads.