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! Euler: A baby on his lap, a cat on his back thats how he wrote his immortal works (origin? Why does setupterm terminate the program? Press question mark to learn the rest of the keyboard shortcuts. A nit: in your version, the cast to void * is unnecessary. The subreddit for the C programming language, Press J to jump to the feed. On all of them int is 32bit, not 16bit. Anw, the project still build and run normally when i use Xcode 5.0 with iOS 7.0. what happens when we typecast normal variable to void* or any pointer variable? Mutually exclusive execution using std::atomic? Converting one datatype into another is known as type casting or, type-conversion. 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. 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. and how to print the thread id of 2d array argument? ../lib/odp-util.c:5665:7: note: expanded from macro 'SCAN_SINGLE' I usually have all automatic conversion warnings effective when developing in C, and I use explicit casting in order to suppress a specific . How do I force make/GCC to show me the commands? Find centralized, trusted content and collaborate around the technologies you use most. How create a simple program using threads in C? Using Kolmogorov complexity to measure difficulty of problems? 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. By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. To learn more, see our tips on writing great answers. Otherwise, if the original pointer value points to an object a, and there is an object b of the . In both cases, converting the pointer to an integer type that's too small to represent all pointer values is a bug. The proper way is to cast it to another pointer type. Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. Therefore it is perfectly valid for the compiler to throw an error for a line like. ^~~~~~~~~~~~~~~~~~~ This is not a conversion at all. Do roots of these polynomials approach the negative of the Euler-Mascheroni constant? To be honest, I think, clang is too restrictive here. Acidity of alcohols and basicity of amines. Connect and share knowledge within a single location that is structured and easy to search. And, most of these will not even work on gcc4. 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. Identify those arcade games from a 1983 Brazilian music video. Infact I know several systems where that does not hold. The text was updated successfully, but these errors were encountered: You signed in with another tab or window. Taking the above declarations of A, D, ch of the . Is it possible to create a concave light? This page was last modified on 12 February 2023, at 18:25. Connect and share knowledge within a single location that is structured and easy to search. Well occasionally send you account related emails. Here is my code: I already tried (void*)M_TABLE_SIZE but then I get an error that I cannot use the * operator. This is known as implicit type casting or type promotion, compiler automatically converts smaller data type to larger data type. Why do small African island nations perform better than African continental nations, considering democracy and human development? You are just making it bigger by tricking the compiler and the ABI. Does melting sea ices rises global sea level? The result is implementation-defined and typically yields the numeric address of the byte in memory that the pointer pointers to. Unless you have a valid address at that value, you are going to invoke undefined behaviour when try to use that pointer. how to cascade 2d int array to 2d void pointer array? This is a fine way to pass integers to new pthreads, if that is what you need. For example, the main thread could wait for all of the other threads to end before terminating. 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. An open (void) pointer can hold a pointer of any type. 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. Please tell me error: cast from 'void*' to 'int' loses precision, How Intuit democratizes AI development across teams through reusability. But gcc always give me a warning, that i cannot cast an int to a void*. I have a function with prototype void* myFcn(void* arg) which is used as the starting point for a pthread. How to use Slater Type Orbitals as a basis functions in matrix method correctly? Does Counterspell prevent from any further spells being cast on a given turn? 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. Asking for help, clarification, or responding to other answers. This page has been accessed 1,655,678 times. Wrong. That could create all kinds of trouble. And you can't pass a pointer to a stack based object from the other thread as it may no longer be valid. It's always a good practice to put your #define's in brackets to avoid such surprise. If you really need such trickery, then consider one of dedicated types, which are intptr_t and uintptr_t. I am an entry level C programmer. 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. However even though their types are different, the address is going to be the same. Where does this (supposedly) Gibson quote come from? To learn more, see our tips on writing great answers. pthread passes the argument as a void*. How do I set, clear, and toggle a single bit? Fork 63. You can use a 64 bits integer instead howerver I usually use a function with the right prototype and I cast the function type : Click to see the query in the CodeQL repository. 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. Or, they are all wrong. What Is the Difference Between 'Man' And 'Son of Man' in Num 23:19? On most platforms pointers and longs are the same size, but ints and pointers often are not the same size on 64bit platforms. Since all pointers on 64-bit Windows are 64 bits, you are growing the data size from 32 bits backto 64 bits. By clicking Sign up for GitHub, you agree to our terms of service and static const void* M_OFFSET = (void*)64*1024; Since gcc compiles that you are performing arithmetic between void* and an int ( 1024 ). Narrowing Casting (manually) - converting a larger type to a . Use returnPtr[j] = (void *) ((long)ptr + i); ). Mutually exclusive execution using std::atomic? It is done by the compiler on its own, without any external trigger from the user. 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. ", "!"? Now, what happens when I run it with the thread sanitizer? I think the solution 3> should be the correct one. 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.. Half your pointer will be garbage. 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. GitHub Skip to content Product Solutions Open Source Pricing Sign in Sign up smadaminov / ovs-dpdk-meson-issues Public Notifications Fork 1 Star 1 Code Issues 66 Pull requests Actions Projects 1 Security Insights New issue What does casting to void* does when passing arguments to variadic functions? warning C4311: 'type cast': pointer truncation from 'void *' to 'long' in ECPG test files. Bulk update symbol size units from mm to map units in rule-based symbology. ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ If you are going to pass the address you typically need to exert some more control over the lifetime of the object. 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. 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. From the question I presume the OP does. What Is the Difference Between 'Man' And 'Son of Man' in Num 23:19? Making statements based on opinion; back them up with references or personal experience. Not the answer you're looking for? The problem just occur with Xcode 5.1. 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. Just edited. 10) A prvalue of type pointer to void (possibly cv-qualified) can be converted to pointer to any object type. The only alternative is really to take time and fix all 64-bit code issues, of which there may be some non-trivial issues. My code is all over the place now but I appreciate you all helping me on my journey to mastery! 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. rev2023.3.3.43278. 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. 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. The problem is not with casting, but with the target type loosing half of the pointer. Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. 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. For example, if you want to store a 'long' value into a simple integer then you can type cast 'long' to 'int'. You can only do this if you use a synchronization primitive to ensure that there is no race condition. 7.1 New Cast Operations The C++ standard defines new cast operations that provide finer control than previous cast operations. x is a local variable and its lifetime ends as soon as control leaves the scope it was defined in. If your standard library (even if it is not C99) happens to provide these types - use them. B language was designed to develop . So reinterpret_cast has casted it to long type and then static_cast safely casts long to int, if you are ready do truncte the data.