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 execute. Computer programs are one component of software, which also includes documentation and other intangible components. A computer program ...

life cycle Life cycle, life-cycle, or lifecycle may refer to: Science and academia *Biological life cycle, the sequence of life stages that an organism undergoes from birth to reproduction ending with the production of the offspring *Life-cycle hypothesis, ...

, in which the code is being

executed Capital punishment, also known as the death penalty, is the state-sanctioned practice of deliberately killing a person as a punishment for an actual or supposed crime, usually following an authorized, rule-governed process to conclude that t ...

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, an ...

(CPU) as

machine code In computer programming, machine code is any low-level programming language, consisting of machine language instructions, which are used to control a computer's central processing unit (CPU). Each instruction causes the CPU to perform a very ...

. In other words, "runtime" is the running phase of a program. A runtime error is detected after or during the execution (running state) of a program, whereas a

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 concept ...

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 that ...

before the program is ever executed.

Type checking In computer programming, a type system is a logical system comprising a set of rules that assigns a property called a type to every "term" (a word, phrase, or other set of symbols). Usually the terms are various constructs of a computer progra ...

register allocation In compiler optimization, register allocation is the process of assigning local automatic variables and expression results to a limited number of processor registers. Register allocation can happen over a basic block (''local 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 A programming language is a system of notation for writing computer programs. Most programming languages are text-based formal languages, but they may also be graphical. They are a kind of computer language. The description of a programming ...

, such as

division by zero In mathematics, division by zero is division (mathematics), division where the divisor (denominator) is 0, zero. Such a division can be formally expression (mathematics), expressed as \tfrac, where is the dividend (numerator). In ordinary ari ...

errors, domain errors, array subscript out of bounds errors,

arithmetic underflow The term arithmetic underflow (also floating point underflow, or just underflow) is a condition in a computer program where the result of a calculation is a number of more precise absolute value than the computer can actually represent in memory o ...

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. __TOC__

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 remembered, ...

setup and links the program with any dynamically linked

libraries A library is a collection of materials, books or media that are accessible for use and not just for display purposes. A library provides physical (hard copies) or digital access (soft copies) materials, and may be a physical location or a vir ...

it needs, and then the execution begins starting from the program's

entry point In computer programming, an entry point is the place in a program where the execution of a program begins, and where the program has access to command line arguments. To start a program's execution, the loader or operating system passes contro ...

. 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 error In computer programming, a logic error is a bug in a program that causes it to operate incorrectly, but not to terminate abnormally (or crash). A logic error produces unintended or undesired output or other behaviour, although it may not immedia ...

s and

array An array is a systematic arrangement of similar objects, usually in rows and columns. Things called an array include: {{TOC right Music * In twelve-tone and serial composition, the presentation of simultaneous twelve-tone sets such that the ...

bounds checking are examples. For this reason, some programming bugs are not discovered until the program is tested in a

production environment In software deployment, an environment or tier is a computer system or set of systems in which a computer program or software component is deployed and executed. In simple cases, such as developing and immediately executing a program on the same m ...

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 In computing and computer programming, exception handling is the process of responding to the occurrence of ''exceptions'' – anomalous or exceptional conditions requiring special processing – during the execution of a program. In general, an ...

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 Automated exception handling is a computing term referring to the computerized handling of errors. Runtime systems (engines) such as those for the Java programming language or .NET Framework lend themselves to an automated mode of exception or er ...

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.

References

{{Reflist Computer libraries Computing platforms Computing terminology

Implementation details

Application errors (exceptions)

See also

References