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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 ...
Program execution; General concepts; Code; Translation. Compiler. Compile time; Optimizing compiler; Intermediate representation (IR); Execution. Runtime system. Runtime
Runtime, run time, or execution time is the final phase of a computer program ' s life cycle, in which the code is being executed on the computer's central processing unit (CPU) as machine code. In other words, "runtime" is the running phase of a program.
Both C and C++ (pre-C++23) do not have native support for obtaining stack traces, but libraries such as glibc and boost provide this functionality. [6] [7] In these languages, some compiler optimizations may interfere with the call stack information that can be recovered at runtime.
The earliest published JIT compiler is generally attributed to work on LISP by John McCarthy in 1960. [4] In his seminal paper Recursive functions of symbolic expressions and their computation by machine, Part I, he mentions functions that are translated during runtime, thereby sparing the need to save the compiler output to punch cards [5] (although this would be more accurately known as a ...
For example, a precondition—an assertion placed at the beginning of a section of code—determines the set of states under which the programmer expects the code to execute. A postcondition—placed at the end—describes the expected state at the end of execution. For example: x > 0 { x++ } x > 1.
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: