Integer conversions, both implicit and explicit (using a cast), must be guaranteed not to result in lost or misinterpreted data. "jacob navia" wrote: This question has probably been asked a million time, but here it comes INT36-C. Converting a pointer to integer or integer to pointer Note that it's not guaranteed that casting an, Generally this kind of type casting does not lead to any concern as long as the addresses are encoded using the same length as the "variable type" (. static const void* M_OFFSET = (void*)64*1024; Since gcc compiles that you are performing arithmetic between void* and an int ( 1024 ). Just edited. On most platforms pointers and longs are the same size, but ints and pointers often are not the same size on 64bit platforms. This is what the second warning is telling you. The following program casts a double to an int. @DavidHeffernan, sane thread APIs wouldn't send integral data to the thread procedures, they would send pointers. ", "!"? Why does Acts not mention the deaths of Peter and Paul? You can use any other pointer, or you can use (size_t), which is 64 bits. pointer/reference to a derived class pointer/reference. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. Can I use the spell Immovable Object to create a castle which floats above the clouds? That could create all kinds of trouble. Cerror: cast to 'void *' from smaller integer type 'int How to set, clear, and toggle a single bit? Content Discovery initiative April 13 update: Related questions using a Review our technical responses for the 2023 Developer Survey, error: cast from void* to int loses precision, cast to pointer from integer of different size, pthread code. 472,096 Members | 2,054 Online. Casting int to void* : r/C_Programming - Reddit My blogs h2 and other tags are in these manner. This is not a conversion at all. Again, all of the answers above missed the point badly. 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. This is not even remotely "the correct answer". rev2023.5.1.43405. This is a fine way to pass integers to new pthreads, if that is what you need. Yeah, the tutorial is doing it wrong. Two MacBook Pro with same model number (A1286) but different year. However, if a conversion cannot be made without a risk of losing information, the compiler requires that you perform an explicit conversion, which is called a cast. In C#, you can perform the following kinds of conversions: Implicit conversions: No special syntax is required because the conversion always succeeds and no data will be lost. I would like to know the reason. For reference types, an implicit conversion always exists from a class to any one of its direct or indirect base classes or interfaces. @ck_ I didn't realize the error in the question is actually an error by default, not a warning-turned-error. Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. 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 rule is particularly true for integer values that originate from untrusted sources and are used in any of the following ways: Integer operands of any pointer arithmetic, including array indexing 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. 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. 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, when you cast a (void*) to (long), you are losing 32 bits of data in the conversion. For example, if the pointers in a system are stored in 16 bits, but integers are stored in 8 bits, a total of 8 bits would be lost in the . Was Aristarchus the first to propose heliocentrism? This allows you to reinterpret the void * as an int. Terrible solution. c - How to cast an integer to void pointer? - Stack Overflow converted back to pointer to void, and the result will compare equal arrays - I get the error: "cast to smaller integer type 'int' from Casting between types - The Rust Programming Language Asking for help, clarification, or responding to other answers. When is casting void pointer needed in C? Because C# is statically-typed at compile time, after a variable is declared, it cannot be declared again or assigned a value of another type unless that type is implicitly convertible to the variable's type. Most answers just try to extract 32 useless bits out of the argument. Usually that means the pointer is allocated with. Half your pointer will be garbage. What were the most popular text editors for MS-DOS in the 1980s? Were sorry. He also rips off an arm to use as a sword. Which reverse polarity protection is better and why? char **array; pthread passes the argument as a void*. Passing negative parameters to a wolframscript, Generating points along line with specifying the origin of point generation in QGIS. For integral types, this means the range of the source type is a proper subset of the range for the target type. . Not the answer you're looking for? To avoid truncating your pointer, cast it to a type of identical size. But this code pass the normal variable .. Why don't we use the 7805 for car phone chargers? it often does reinterpret_cast<uint32_t> (ptr). 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). How to force Unity Editor/TestRunner to run at full speed when in background? A good thing in general, but if you want to disable the warning, just do it. MIP Model with relaxed integer constraints takes longer to solve than normal model, why? UDF for multiples heterogenous reactions - CFD Online Not the answer you're looking for? Casting int to void* loses precision, and what is the solution in required cases, c++: cast from "const variable*" to "uint32" loses precision, cast from 'char*' to 'int' loses precision. Put your define inside a bracket: #define M_TABLE_SIZE (64*1024) Now, you can do: static const void* M_OFFSET = (void*) M_TABLE_SIZE; without a problem. Not the answer you're looking for? void* -> integer -> void* rather than integer -> void* -> integer. BUT converting a pointer to void* and back again is well supported (everywhere). Can my creature spell be countered if I cast a split second spell after it? I am compiling this program in linux gcc compiler.. does lazarbeam have a wife; Books. 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 sense in writing a few dozen lines of extra code just to get a bunch of numbered threads. pthread create managing values generated in function (in c), Establishing TCP socket connection between PHP client and C server on Ubuntu. If a negative integer value is converted to an unsigned type, the resulting value corresponds to its 2's complement bitwise representation (i.e., If the conversion is from a floating-point type to an integer type, the value is truncated (the decimal part is removed). 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. 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. casting from int to void* and back to int. 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. Why does flowing off the end of a non-void function without returning a value not produce a compiler error? If this is the data to a thread procedure, then you quite commonly want to pass by value. 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). By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. (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, , i 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 a downhill scooter lighter than a downhill MTB with same performance? How to Cast a void* ponter to a char without a warning? Asking for help, clarification, or responding to other answers. is there such a thing as "right to be heard"? Clang warnings for an invalid casting? - The FreeBSD Forums Asking for help, clarification, or responding to other answers. Why did US v. Assange skip the court of appeal? 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. @DavidHeffernan I rephrased that sentence a little. Casting is required when information might be lost in the conversion, or when the conversion might not succeed for other reasons. Is it safe to publish research papers in cooperation with Russian academics? This is why you got Error 1 C2036, from your post. 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. By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. You might want to typedef, You should change your code to handle this. You can use a 64 bits integer instead howerver I usually use a function with the right prototype and I cast the function type : Alternatively, if you choose to castthe ptr variableto (size_t) instead, then you don't need to worry about the pointer typeanymore. Thanks for contributing an answer to Stack Overflow! Implicit conversions - cppreference.com Mar 30, 2020 at 11:12am By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. These kinds of operations are called type conversions. While working with Threads in C, I'm facing the warning, "warning: cast to pointer from integer of different size". Converting a void* to an int is non-portable way that may work or may not! There's no proper way to cast this to int in general case. how to convert void* to int - C++ Forum - cplusplus.com Content Discovery initiative April 13 update: Related questions using a Review our technical responses for the 2023 Developer Survey, xcode build error: Semantic issue cast from pointer to smaller type 'int' loses information. Cvoid*int - Alan_LJP - Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. Type conversions - cplusplus.com cwindowccwindowsword[3]={"ab"};_ab charPersondebug, A, A, , "C" ???? As a result, it is possible to silently convert from one pointer type to another without the compiler diagnosing the problem by storing or casting a pointer to void * and then storing or casting it to the final type. What I am trying to do in that line of code is check to make sure each character in my string is alphabetical. How do I check if a string represents a number (float or int)? Since the culprit is probably something like -Wall which enables many warnings you should keep on, you should selectively disable this single warning. The content you requested has been removed. 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. rev2023.5.1.43405. For example, you might have an integer variable that you need to pass to a method whose parameter is typed as double. No special syntax is necessary because a derived class always contains all the members of a base class. Technically, these casts should therefore be valid. that any valid pointer to void can be converted to this type, then I need to convert the argument to an int for later use: The compiler (GCC version 4.2.4) returns the error: You can cast it to an intptr_t type. /** Dynamically allocate a 2d (x*y) array of elements of size _size_ bytes. Interpreting non-statistically significant results: Do we have "no evidence" or "insufficient evidence" to reject the null? From the question I presume the OP does. (void *)(long)i, Copyright 2011-2023 SegmentFault. Did the Golden Gate Bridge 'flatten' under the weight of 300,000 people in 1987? #, In a 64 bit machine with sizeof(int) == 4. I had this error while trying to cross compile the header from libstdc++ 5.4.0 with clang 7.0.1 for ARM. Going through them one by one would be very tedious and since this is an experimental project anyway, I'm happy to settle for a "hackish" workaround. More info about Internet Explorer and Microsoft Edge, How to convert between hexadecimal strings and numeric types, How to safely cast using pattern matching and the as and is operators. How to use Clang static analyzer with a Cortex-M project? what happens when we typecast normal variable to void* or any pointer variable? If you need to keep the returned address, just keep it as void*. @Martin York: No, it doesn't depend on endiannness. In this case, casting the pointer back to an integer is meaningless, because . How a top-ranked engineering school reimagined CS curriculum (Ep. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. What is the difference between const int*, const int * const, and int const *? Explicitly call a single-argument constructor or a conversion operator. My code is all over the place now but I appreciate you all helping me on my journey to mastery! Connect and share knowledge within a single location that is structured and easy to search. 565), Improving the copy in the close modal and post notices - 2023 edition, New blog post from our CEO Prashanth: Community is the future of AI. Conversions with helper classes: To convert between non-compatible types, such as integers and System.DateTime objects, or hexadecimal strings and byte arrays, you can use the System.BitConverter class, the System.Convert class, and the Parse methods of the built-in numeric types, such as Int32.Parse. Please tell me error: cast from 'void*' to 'int' loses precision, How a top-ranked engineering school reimagined CS curriculum (Ep. Is a downhill scooter lighter than a downhill MTB with same performance? To perform a cast, specify the type that you are casting to in parentheses in front of the value or variable to be converted. casting from int to void* and back to int - C / C++ Which was the first Sci-Fi story to predict obnoxious "robo calls"? I think that's what you want: // Declaration uint8_t *myData; void loop () { myData = "custom string"; } (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 10.8k 2 21 2015-06-05 it often does reinterpret_cast(ptr). How a top-ranked engineering school reimagined CS curriculum (Ep. cast to void *' from smaller integer type 'int Short story about swapping bodies as a job; the person who hires the main character misuses his body. The proper way is to cast it to another pointer type. Nov 14 '05
The compiler is perfectly correct & accurate! I guess the other important fact is that the cast operator has higher precedence that the multiplication operator. INT31-C. Ensure that integer conversions do not result in lost or User without create permission can create a custom object from Managed package using Custom Rest API. For some type X he has: And you can't pass a pointer to a stack based object from the other thread as it may no longer be valid. Find centralized, trusted content and collaborate around the technologies you use most. I've always been a little sketchy on the differences between static, "Signpost" puzzle from Tatham's collection. Does a password policy with a restriction of repeated characters increase security? Both languages have been widely adopted by How to plot text in color? 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! Just want to point out that the purpose of threads is, +1 absolutely true, but if you take you time to write struct {}, you can save a lot of troubles in the future when you want to receive/send more data then just an int. A boy can regenerate, so demons eat him for years. Where can I find a clear diagram of the SPECK algorithm? Thanks in A colleague asked me something along the lines of the following today. Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. Unfortunately, that hardware is 64-bit and the code contains many instances of pointer arithmetic that expects pointers to be 32-bit, i.e. How do I work around the GCC "error: cast from SourceLocation* to int loses precision" error when compiling cmockery.c? it means that myData is a variable of type "pointer to uint8_t", but it doesn't point to anything yet. this way you won't get any warning. In both cases, converting the pointer to an integer type that's too small to represent all pointer values is a bug. 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. To learn more, see our tips on writing great answers. Don't do that. even though the compiler doesn't know you only ever pass myFcn to pthread_create in conjunction with an integer. 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. Say you hack this successfully. What differentiates living as mere roommates from living in a marriage-like relationship? Making statements based on opinion; back them up with references or personal experience. c - Cast int to void* - Stack Overflow rev2023.5.1.43405. Please start a new discussion. c - type casting integer to void* - Stack Overflow If the function had the correct signature you would not need to cast it explicitly.
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