Bus Error Example In C
Contents |
here for a quick overview of the site Help Center Detailed answers to any questions you might have Meta Discuss the workings and policies of this site About Us Learn more about Stack Overflow the company Business Learn
Bus Error 10 C
more about hiring developers or posting ads with us Stack Overflow Questions Jobs Documentation Tags Users c bus error core dumped Badges Ask Question x Dismiss Join the Stack Overflow Community Stack Overflow is a community of 4.7 million programmers, just like you, helping bus error in c program each other. Join them; it only takes a minute: Sign up What is a bus error? up vote 155 down vote favorite 49 What does the "bus error" message mean, and how does it differ from a segfault?
Runtime Error Example In C
c unix segmentation-fault bus-error share|improve this question edited Oct 18 '15 at 10:44 Cool Guy 15.8k51952 asked Oct 17 '08 at 14:48 raldi 7,239216178 add a comment| 15 Answers 15 active oldest votes up vote 150 down vote accepted Bus errors are rare nowadays on x86 and occur when your processor cannot even attempt the memory access requested, typically: using a processor instruction with an address that does not satisfy its alignment requirements. Segmentation faults occur
Logical Error Example In C
when accessing memory which does not belong to your process, they are very common and are typically the result of: using a pointer to something that was deallocated. using an uninitialized hence bogus pointer. using a null pointer. overflowing a buffer. PS: To be more precise this is not manipulating the pointer itself that will cause issues, it's accessing the memory it points to (dereferencing). share|improve this answer edited Oct 17 '08 at 15:18 answered Oct 17 '08 at 15:12 bltxd 5,70322336 52 They aren't rare; I'm just at Exercise 9 from How to Learn C the Hard Way and already encountered one... –11684 Mar 26 '13 at 20:12 5 Another cause of bus errors (on Linux anyway) is when the operating system can't back a virtual page with physical memory (e.g. low-memory conditions or out of huge pages when using huge page memory.) Typically mmap (and malloc) just reserve the virtual address space, and the kernel assigns the physical memory on demand (so called soft page faults.) Make a large enough malloc, and then write to enough of it and you'll get a bus error. –Eloff Jul 14 '15 at 0:09 add a comment| up vote 55 down vote A segfault is accessing memory that you're not allowed to access. It's read-only, you don't have permission, etc... A bus error is trying to access memor
challenged and removed. (July 2015) (Learn how and when to remove this template message) In computing, a bus error is a fault raised bus error linux by hardware, notifying an operating system (OS) that a process is
Bus Error 10 Mac
trying to access memory that the CPU cannot physically address: an invalid address for the address fortran bus error bus, hence the name. In modern use on most architectures these are much rarer than segmentation faults, which occur primarily due to memory access violations: problems in the http://stackoverflow.com/questions/212466/what-is-a-bus-error logical address or permissions. On POSIX-compliant platforms, bus errors usually result in the SIGBUS signal being sent to the process that caused the error. SIGBUS can also be caused by any general device fault that the computer detects, though a bus error rarely means that the computer hardware is physically broken—it is normally caused by https://en.wikipedia.org/wiki/Bus_error a bug in a program's source code.[citation needed] Bus errors may also be raised for certain other paging errors; see below. Contents 1 Causes 1.1 Non-existent address 1.2 Unaligned access 1.3 Paging errors 2 Example 3 References Causes[edit] There are at least three main causes of bus errors: Non-existent address[edit] Software instructs the CPU to read or write a specific physical memory address. Accordingly, the CPU sets this physical address on its address bus and requests all other hardware connected to the CPU to respond with the results, if they answer for this specific address. If no other hardware responds, the CPU raises an exception, stating that the requested physical address is unrecognized by the whole computer system. Note that this only covers physical memory addresses. Trying to access an undefined virtual memory address is generally considered to be a segmentation fault rather than a bus error, though if the MMU is separate, the processor can't tell the difference. Unaligned access[edit] Most
in 1995. Last modification: Tue Jan 13 13:12:09 EST 2015 TYPES in C In C, there are three kinds of types that variables can have -- scalars, aggregates, and pointers. Half of the game in getting things right in C is keeping yourself from being confused about types. http://web.eecs.utk.edu/courses/spring2016/cosc360/360/notes/CStuff/lecture.html This lecture tries to elaborate on this a little. Scalar Types There are 7 scalar types in C: char -- 1 byte short -- 2 bytes int -- 4 bytes long -- 4 or http://www.glue.umd.edu/afs/glue.umd.edu/system/info/olh/Utilities/Unix_answers/unix_bus_or_seg.html 8 bytes, depending on the system and compiler float -- 4 bytes double -- 8 bytes (pointer -- 4 or 8 bytes, depending on the system and compiler) These should all be familiar bus error to you (ok, maybe not a short, but the rest should). If you want to verify or use the size of a type in C, you use the macro sizeof(). For example, sizeof(long) will return either 4 or 8, depending on how big a long is in your system. You can declare a scalar variable in one of three places: As a global variable, as a procedure error example in parameter, and as a local variable. For example, look at the program below in p1.c: (In this and all other lecture notes, you can copy the programs and the makefile into your own directory, and then compile them by using make. E.g. to make the program p1, you say ``make p1''). #include
program yourself, you can skip the rest of this section. For College-supported software, you can report the bug by contacting a consultant through olc or "mail staff". ------------------------------------------------------------------------------- If the program displays this message: Bus error or Segmentation fault or Core dump ... then the program was trying to access a memory location outside its address space. The computer detected this problem and sent a signal to your program, which caused it to abort. Things that cause bus errors and segmentation violations are typically out-of-bounds array references and/or references through uninitialized or mangled pointers. Look very closely in your program for bizarre things like that. A common example in C is: int c; scanf("%d", c); instead of the correct version: int c; scanf("%d", &c); An example from C++ is: int* p=new int[100]; cout<< p[100]; instead of the correct version: int* p=new int[100]; cout << p[99] (remember array referances in C and C++ start with 0 ) There are a number of methods for finding out where the program went out of bounds. One method is to use printf() statements to determine how far the program is getting before it crashes, and to print out the contents of interesting variables. A more sophisticated method is using 'dbx', a source level symbolic debugger. C and C++ programmers can also use 'gdb'. To learn about 'dbx', you can read the manual pages by using the 'man' command, as in: man dbx To learn about 'gdb', you can read the manual node in the 'xinfo' program, or using 'M-x info' in Emacs. If you need to debug your program, you may want to enable a core dump. Usually, those two messages above would also have "(core dumped)" by them, indicating that the program wrote an image of its current memory into a file called "core" in that directory. You might want to type 'fs lq' and find out how many blocks (kilobytes) you have available in your quota. Then you can type, say: limit coredumpsize 100 .. to limit your core dump size to 100K for your current login. BE CAREFUL not to let yoursel