In
computer science
Computer science is the study of computation, automation, and information. Computer science spans theoretical disciplines (such as algorithms, theory of computation, information theory, and automation) to Applied science, practical discipli ...
, runtime, run time, or execution time is the final phase of a
computer program
A computer program is a sequence or set of instructions in a programming language for a computer to Execution (computing), execute. Computer programs are one component of software, which also includes software documentation, documentation and oth ...
s
life cycle, in which the code is being
executed on the computer's
central processing unit
A central processing unit (CPU), also called a central processor, main processor or just processor, is the electronic circuitry that executes instructions comprising a computer program. The CPU performs basic arithmetic, logic, controlling, a ...
(CPU) as
machine code. In other words, "runtime" is the running phase of a program.
A
runtime error
In computer science, runtime, run time, or execution time is the final phase of a computer programs 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 ...
is detected after or during the execution (running state) of a program, whereas a
compile-time error is detected by the
compiler
In computing, a compiler is a computer program that translates computer code written in one programming language (the ''source'' language) into another language (the ''target'' language). The name "compiler" is primarily used for programs tha ...
before the program is ever executed.
Type checking,
register allocation,
code generation, and code optimization are typically done at compile time, but may be done at runtime depending on the particular language and compiler. Many other runtime errors exist and are handled differently by different
programming languages, such as
division by zero errors, domain errors,
array subscript out of bounds errors,
arithmetic underflow errors, several types of underflow and
overflow errors, and many other runtime errors generally considered as software bugs which may or may not be caught and handled by any particular computer language.
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Implementation details
When a program is to be executed, a
loader
Loader can refer to:
* Loader (equipment)
* Loader (computing)
** LOADER.EXE, an auto-start program loader optionally used in the startup process of Microsoft Windows ME
* Loader (surname)
* Fast loader
* Speedloader
* Boot loader
** LOADER.COM ...
first performs the necessary
memory
Memory is the faculty of the mind by which data or information is encoded, stored, and retrieved when needed. It is the retention of information over time for the purpose of influencing future action. If past events could not be remember ...
setup and links the program with any
dynamically linked libraries it needs, and then the execution begins starting from the program's
entry point. In some cases, a language or implementation will have these tasks done by the language runtime instead, though this is unusual in mainstream languages on common consumer operating systems.
Some program debugging can only be performed (or is more efficient or accurate when performed) at runtime.
Logic errors and
array bounds checking are examples. For this reason, some programming
bugs are not discovered until the program is tested in a
production environment with real data, despite sophisticated compile-time checking and pre-release testing. In this case, the end-user may encounter a "runtime error" message.
Application errors (exceptions)
Exception handling is one language feature designed to handle runtime errors, providing a structured way to catch completely unexpected situations as well as predictable errors or unusual results without the amount of inline error checking required of languages without it. More recent advancements in runtime engines enable
automated exception handling which provides "root-cause" debug information for every exception of interest and is implemented independent of the source code, by attaching a special software product to the runtime engine.
See also
*
Compile time
In computer science, compile time (or compile-time) describes the time window during which a computer program is compiled.
The term is used as an adjective to describe concepts related to the context of program compilation, as opposed to concep ...
and
compiling
In computing, a compiler is a computer program that translates computer code written in one programming language (the ''source'' language) into another language (the ''target'' language). The name "compiler" is primarily used for programs tha ...
*
Interpreter (computing)
In computer science, an interpreter is a computer program that directly executes instructions written in a programming or scripting language, without requiring them previously to have been compiled into a machine language program. An interpret ...
*
Runtime type information
*
Runtime system
*
Runtime library
In computer programming, a runtime library is a set of low-level routines used by a compiler to invoke some of the behaviors of a runtime environment, by inserting calls to the runtime library into compiled executable binary. The runtime enviro ...
References
{{Reflist
Computer libraries
Computing platforms
Computing terminology