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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 ...
In the early versions of C, undefined behavior's primary advantage was the production of performant compilers for a wide variety of machines: a specific construct could be mapped to a machine-specific feature, and the compiler did not have to generate additional code for the runtime to adapt the side effects to match semantics imposed by the ...
However, dynamic compilation can still technically have compilation errors, [citation needed] although many programmers and sources may identify them as run-time errors. Most just-in-time compilers, such as the Javascript V8 engine, ambiguously refer to compilation errors as syntax errors since they check for them at run time. [1] [2]
Types of code; Source code; Object code; Bytecode; Machine code; Microcode; Compilation strategies; Ahead-of-time (AOT) Just-in-time (JIT) Tracing just-in-time; Compile and go system; Precompilation; Transcompilation; Recompilation; Notable runtimes; Android Runtime (ART) BEAM (Erlang) Common Language Runtime (CLR) and Mono; CPython and PyPy ...
C does not provide direct support to exception handling: it is the programmer's responsibility to prevent errors in the first place and test return values from the functions.
This sample code creates a null pointer, and then tries to access its value (read the value). Doing so causes a segmentation fault at runtime on many operating systems. Dereferencing a null pointer and then assigning to it (writing a value to a non-existent target) also usually causes a segmentation fault:
All garbage-collected languages take this approach. [1] For C and C++, many tools exist that perform a compile-time transformation of the code to do memory safety checks at runtime, such as CheckPointer [21] and AddressSanitizer which imposes an average slowdown factor of 2. [22]
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