In computer science

Computer science

Computer science or computing science is the study of the theoretical foundations of information and computation and of practical techniques for their implementation and application in computer systems...

, link time refers to either the operations performed by a linker (ie, link time operations) or programming language

Programming language

A programming language is an artificial language designed to communicate instructions to a machine, particularly a computer. Programming languages can be used to create programs that control the behavior of a machine and/or to express algorithms precisely....

 requirements that must be met by compiled source code

Source code

In computer science, source code is text written using the format and syntax of the programming language that it is being written in. Such a language is specially designed to facilitate the work of computer programmers, who specify the actions to be performed by a computer mostly by writing source...

 for it to be successfully linked (ie, link time requirements).

The operations performed at link time usually include fixing up the addresses of externally referenced objects and functions, various kinds of cross module checks (eg, type checks

Data type

In computer programming, a data type is a classification identifying one of various types of data, such as floating-point, integer, or Boolean, that determines the possible values for that type; the operations that can be done on values of that type; the meaning of the data; and the way values of...

 on externally visible identifiers and in some languages instantiation of template

Generic programming

In a broad definition, generic programming is a style of computer programming in which algorithms are written in terms of to-be-specified-later types that are then instantiated when needed for specific types provided as parameters...

). Some optimizing compilers

Compiler optimization

Compiler optimization is the process of tuning the output of a compiler to minimize or maximize some attributes of an executable computer program. The most common requirement is to minimize the time taken to execute a program; a less common one is to minimize the amount of memory occupied...

 delay code generation until link time because it is here that information about a complete program is available to them.

The definition of a programming language may specify link time requirements that source code must meet to be successfully compiled (eg, the maximum number of characters in an externally visible identifier that must be considered significant).

Link time occurs after compile time

Compile time

In computer science, compile time refers to either the operations performed by a compiler , programming language requirements that must be met by source code for it to be successfully compiled , or properties of the program that can be reasoned about at compile time.The operations performed at...

 and before runtime (when a program

Computer program

A computer program is a sequence of instructions written to perform a specified task with a computer. A computer requires programs to function, typically executing the program's instructions in a central processor. The program has an executable form that the computer can use directly to execute...

 is executed). In some programming languages it may be necessary for some compilation and linking to occur at runtime.