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The final value of k is undefined. The answer that it must be 10 assumes that it started at zero, which may or may not be true. Note that in the example, the variable i is initialized to zero by the first clause of the for statement. Another example can be when dealing with structs.
Here is an example of ANSI C code that will generally cause a segmentation fault on platforms with memory protection. It attempts to modify a string literal, which is undefined behavior according to the ANSI C standard. Most compilers will not catch this at compile time, and instead compile this to executable code that will crash:
A straightforward example is shown below: { char * dp = NULL ; /* ... */ { char c ; dp = & c ; } /* c falls out of scope */ /* dp is now a dangling pointer */ } If the operating system is able to detect run-time references to null pointers , a solution to the above is to assign 0 (null) to dp immediately before the inner block is exited.
An undefined variable in the source code of a computer program is a variable that is accessed in the code but has not been declared by that code. [1] In some programming languages, an implicit declaration is provided the first time such a variable is encountered at compile time. In other languages such a usage is considered to be sufficiently ...
Aliasing can occur in any language that can refer to one location in memory with more than one name (for example, with pointers).This is a common problem with functions that accept pointer arguments, and their tolerance (or the lack thereof) for aliasing must be carefully documented, particularly for functions that perform complex manipulations on memory areas passed to them.
It is the responsibility of the programmer to write code that never invokes undefined behavior, although compiler implementations are allowed to issue diagnostics when this happens. Compilers nowadays have flags that enable such diagnostics, for example, -fsanitize=undefined enables the "undefined behavior sanitizer" in gcc 4.9 [2] and in clang ...
ioctl calls minimize the complexity of the kernel's system call interface. However, by providing a place for developers to "stash" bits and pieces of kernel programming interfaces, ioctl calls complicate the overall user-to-kernel API. A kernel that provides several hundred system calls may provide several thousand ioctl calls.
After recompiling a kernel binary image from source code, a kernel panic while booting the resulting kernel is a common problem if the kernel was not correctly configured, compiled or installed. [8] Add-on hardware or malfunctioning RAM could also be sources of fatal kernel errors during start up, due to incompatibility with the OS or a missing ...