computer programming Computer programming is the process of performing a particular computation (or more generally, accomplishing a specific computing result), usually by designing and building an executable computer program. Programming involves tasks such as anal ...

, a runtime library is a set of low-level routines used by a

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 ...

to invoke some of the behaviors of a

runtime environment In computer programming, a runtime system or runtime environment is a sub-system that exists both in the computer where a program is created, as well as in the computers where the program is intended to be run. The name comes from the compile ...

, by inserting calls to the runtime library into compiled executable binary. The runtime environment implements the

execution model A programming language consists of a grammar/syntax plus an execution model. The execution model specifies the behavior of elements of the language. By applying the execution model, one can derive the behavior of a program that was written in term ...

, built-in functions, and other fundamental behaviors of a

programming language 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 ...

. During execution ( run time) of that

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 ...

, execution of those calls to the runtime library cause communication between the executable binary and the runtime environment. A runtime library often includes built-in functions for memory management or

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 ...

. Therefore, a runtime library is always specific to the platform and compiler. The runtime library may implement a portion of the runtime environment's behavior, but if one reads the code of the calls available, they are typically only thin wrappers that simply package information, and send it to the runtime environment or operating system. However, sometimes the term ''runtime library'' is meant to include the code of the runtime environment itself, even though much of that code cannot be directly reached via a library call. For example, some language features that can be performed only (or are more efficient or accurate) at runtime are implemented in the runtime environment and may be invoked via the runtime library API, e.g. some logic errors, array

bounds checking In computer programming, bounds checking is any method of detecting whether a variable is within some bounds before it is used. It is usually used to ensure that a number fits into a given type (range checking), or that a variable being used as ...

, dynamic type checking, exception handling, and possibly debugging functionality. For this reason, some programming bugs are not discovered until the program is tested in a "live" environment with real data, despite sophisticated compile-time checking and testing performed during development. As another example, a runtime library may contain code of built-in low-level operations too complicated for their

inlining In computing, inline expansion, or inlining, is a manual or compiler optimization that replaces a function call site with the body of the called function. Inline expansion is similar to macro expansion, but occurs during compilation, without cha ...

during compilation, such as implementations of arithmetic operations not directly supported by the targeted CPU, or various miscellaneous compiler-specific operations and directives. The concept of a ''runtime library'' should not be confused with an ordinary

program library In computer science, a library is a collection of non-volatile resources used by computer programs, often for software development. These may include configuration data, documentation, help data, message templates, pre-written code and subro ...

like that created by an application programmer or delivered by a third party, nor with a

dynamic library In computing, a dynamic linker is the part of an operating system that loads and links the shared libraries needed by an executable when it is executed (at " run time"), by copying the content of libraries from persistent storage to RAM, filli ...

, meaning a program library linked at run time. For example, the

C programming language ''The C Programming Language'' (sometimes termed ''K&R'', after its authors' initials) is a computer programming book written by Brian Kernighan and Dennis Ritchie, the latter of whom originally designed and implemented the language, as well a ...

requires only a minimal runtime library (commonly called

crt0 



 (also known as ) is a set of execution startup routines  linked into a  C program that performs any initialization work required before calling the program's main function. 
 Form and usage
Crt0 generally takes the form of an object file called ...

), but defines a large standard library (called

C standard library The C standard library or libc is the standard library for the C programming language, as specified in the ISO C standard. ISO/IEC (2018). '' ISO/IEC 9899:2018(E): Programming Languages - C §7'' Starting from the original ANSI C standard, it was ...

) that has to be provided by each implementation.

References

{{Reflist

External links

What is the C runtime library?
(

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) Computer libraries Run-time systems

See also

References

External links