Runtime vs Compile time

Question

What is the difference between run-time and compile-time

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Basically if your compiler can work out what you mean or what a value is "at compile time" it can hardcode this into the runtime code. Obviously if your runtime code has to do a calculation every time it will run slower, so if you can determine something at compile time it is much better.

Eg.

Constant folding:

If I write:

int i = 2;
i += MY_CONSTANT;

The compiler can perform this calulation at compile time because it knows what 2 is, and what MY_CONSTANT is. As such it saves itself from performing a calculation every single execution.

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Translation of source code into stuff-happening-on-the- screen disk network  can occur in  roughly  two ways  call them compiling and interpreting   In a compiled program  examples are c and fortran     The source code is fed into another program  usually called a compiler--go figure   which produces an executable program  or an error   The executable is run  by double clicking it  or typing it s name on the command line    Things that happen in the first step are said to happen at  compile time   things that happen in the second step are said to happen at  run time    In an interpreted program  example MicroSoft basic  on dos  and python  I think      The source code is fed into another program  usually called an interpreter  which  runs  it directly  Here the interpreter serves as an intermediate layer between your program and the operating system  or the hardware in really simple computers     In this case the difference between compile time and run time is rather harder to pin down  and much less relevant to the programmer or user   Java is a sort of hybrid  where the code is compiled to bytecode  which then runs on a virtual machine which is usually an interpreter for the bytecode   There is also an intermediate case in which the program is compiled to bytecode and run immediately  as in awk or perl

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In simply word difference b w Compile time  amp  Run time   compile time Developer writes the program in  java format  amp  converts in to the Bytecode which is a class file during this compilation any error occurs can be defined as compile time error   Run time The generated  class file is use by the application for its additional functionality  amp  the logic turns out be wrong and throws an error which is a run time error

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Hmm  ok well  runtime is used to describe something that occurs when a program is running   Compile time is used to describe something that occurs when a program is being built  usually  by a compiler

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Here is a quote from Daniel Liang  author of  Introduction to JAVA programming   on the subject of compilation        A program written in a high-level language is called a source program or source code  Because a computer cannot execute a source program  a source program must be translated into machine code for execution  The translation can be done using another programming tool called an interpreter or a compiler    Daniel Liang   Introduction to JAVA programming   p8         He Continues         A compiler translates the entire source code into a machine-code file  and the machine-code file is then executed    When we punch in high-level human-readable code this is  at first  useless  It must be translated into a sequence of  electronic happenings  in your tiny little CPU  The first step towards this is compilation    Simply put  a compile-time error happens during this phase  while a run-time error occurs later    Remember  Just because a program is compiled without error does not mean it will run without error   A Run-time error will occur in the ready  running or waiting part of a programs life-cycle while a compile-time error will occur prior to the  New  stage of the life cycle    Example of a Compile-time error    A Syntax Error - how can your code be compiled into machine level instructions if they are ambiguous   Your code needs to conform 100  to the syntactical rules of the language otherwise it cannot be compiled into working machine code    Example of a run-time error   Running out of memory - A call to a recursive function for example might lead to stack overflow given a variable of a particular degree  How can this be anticipated by the compiler   it cannot    And that is the difference between a compile-time error and a run-time error

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Here is an extension to the Answer to the question  difference between run-time and compile-time   -- Differences in overheads associated with run-time and compile-time    The run-time performance of the product contributes to its quality by delivering results faster  The compile-time performance of the product contributes to its timeliness by shortening the edit-compile-debug cycle  However  both run-time performance and compile-time performance are secondary factors in achieving timely quality  Therefore  one should consider run-time and compile-time performance improvements only when justified by improvements in overall product quality and timeliness   A great source for further reading here

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Imagine that you are a boss and you have an assistant and a maid  and you give them a list of tasks to do  the assistant  compile time  will grab this list and make a checkup to see if the tasks are understandable and that you didn t write in any awkward language or syntax  so he understands that you want to assign someone for a Job so he assign him for you and he understand that you want some coffee  so his role is over and the maid  run time starts to run those tasks so she goes to make you some coffee but in sudden she doesn   t find any coffee to make so she stops making it or she acts differently and make you some tea  when the program acts differently because he found an error

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Compile-time  the time period in which you  the developer  are compiling your code   Run-time  the time period which a user is running your piece of software   Do you need any clearer definition

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Compile Time   Things that are done at compile time incur  almost  no cost when the resulting program is run  but might incur a large cost when you build the program  Run-Time   More or less the exact opposite  Little cost when you build  more cost when the program is run   From the other side  If something is done at compile time  it runs only on your machine and if something is run-time  it run on your users machine

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It s not a good question for S O   it s not a specific programming question   but it s not a bad question in general   If you think it s trivial  what about read-time vs compile-time  and when is this a useful distinction to make   What about languages where the compiler is available at runtime   Guy Steele  no dummy  he  wrote 7 pages in CLTL2 about EVAL-WHEN  which CL programmers can use to control this   2 sentences are barely enough for a definition  which itself is far short of an explanation   In general  it s a tough problem that language designers have seemed to try to avoid  They often just say  here s a compiler  it does compile-time things  everything after that is run-time  have fun    C is designed to be simple to implement  not the most flexible environment for computation   When you don t have the compiler available at runtime  or the ability to easily control when an expression is evaluated  you tend to end up with hacks in the language to fake common uses of macros  or users come up with Design Patterns to simulate having more powerful constructs   A simple-to-implement language can definitely be a worthwhile goal  but that doesn t mean it s the end-all-be-all of programming language design    I don t use EVAL-WHEN much  but I can t imagine life without it    And the problemspace around compile-time and run-time is huge and still largely unexplored   That s not to say S O  is the right place to have the discussion  but I encourage people to explore this territory further  especially those who have no preconceived notions of what it should be   The question is neither simple nor silly  and we could at least point the inquisitor in the right direction   Unfortunately  I don t know any good references on this   CLTL2 talks about it a bit  but it s not great for learning about it

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Compile Time   Things that are done at compile time incur  almost  no cost when the resulting program is run  but might incur a large cost when you build the program   Run-Time   More or less the exact opposite  Little cost when you build  more cost when the program is run   From the other side  If something is done at compile time  it runs only on your machine and if something is run-time  it run on your users machine   Relevance  An example of where this is important would be a unit carrying type  A compile time version  like Boost Units or my version in D  ends up being just as fast as solving the problem with native floating point code while a run-time version ends up having to pack around information about the units that a value are in and perform checks in them along side every operation  On the other hand  the compile time versions requiter that the units of the values be known at compile time and can t deal with the case where they come from run-time input

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For example  In a strongly typed language  a type could be checked at compile time or at runtime  At compile time it means  that the compiler complains if the types are not compatible  At runtime means  that you can compile your program just fine but at runtime  it throws an exception

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I have always thought of it relative to program processing overhead and how it affects preformance as previously stated  A simple example would be  either defining the absolute memory required for my object in code or not    A defined boolean takes x memory this is then in the compiled program and cannot be changed  When the program runs it knows exactly how much memory to allocate for x    On the other hand if I just define a generic object type  i e  kind of a undefined place holder or maybe a pointer to some giant blob  the actual memory required for my object is not known until the program is run and I assign something to it  thus it then must be evaluated and memory allocation  etc  will be then handled dynamically at run time  more run time overhead     How it is dynamically handled would then depend on the language  the compiler  the OS  your code  etc   On that note however it would really depends on the context in which you are using run time vs compile time

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Run time means something happens when you run the program   Compile time means something happens when you compile the program

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public class RuntimeVsCompileTime    public static void main String   args           test new D     COMPILETIME ERROR                Compiler knows that B is not an instance of A             test new B               compiler has no hint whether the actual type is A  B or C    C c    C a  will be checked during runtime     param a     public static void test A a        C c    C a   RUNTIME ERROR        class A       class B extends A       class C extends A       class D

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IMHO you need to read many links   resources to make an idea about the difference between Runtime vs Compile time because it is a very complex subject    I have list below some of this pictures links that I am recommend     Apart from what it is said above I want to add that sometimes a picture worth 1000 words     the order of this two  first is compile time and then you run A compiled program can be opened and run by a user  When an application is running  it is called runtime   compile time and then runtime1       CLR diag compile time and then runtime2    from Wiki     https   en wikipedia org wiki Run time https   en wikipedia org wiki Run time  program lifecycle phase   Run time  run-time  or runtime may refer to   Computing  Run time  program lifecycle phase   the period during which a computer program is executing  Runtime library  a program library designed to implement functions built into a programming language  Runtime system  software designed to support the execution of computer programs  Software execution  the process of performing instructions one by one during the run time phase           List of compilers    https   en wikipedia org wiki List of compilers   search on google and compare runtime errors vs compile errors            In my opinion a very important thing to know   3 1 the difference between build vs compile and the Build Lifecycle https   maven apache org guides introduction introduction-to-the-lifecycle html   3 2 the difference between this 3 things   compile vs build  vs runtime   https   www quora com What-is-the-difference-between-build-run-and-compile Fernando Padoan  A developer that s just a bit curious for language design Answered Feb 23 I   m going backwards in relation to other answers   running is getting some binary executable  or a script  for interpreted languages  to be  well    executed as a new process on the computer  compiling is the process of parsing a program written in some high level language  higher if compared to machine code   checking it   s syntax  semantics  linking libraries  maybe doing some optimization  then creating a binary executable program as an output  This executable may be in the form of machine code  or some kind of byte code     that is  instructions targeting some kind of virtual machine  building usually involves checking and providing dependencies  inspecting code  compiling the code into binary  running automated tests and packaging the resulting binary ies  and other assets  images  configuration files  libraries  etc   into some specific format of deployable file  Note that most processes are optional and some depend on the targeted platform you are building for  As an example  packaging a Java application for Tomcat will output a  war file  Building a Win32 executable out of C   code could just output the  exe program  or could also package it inside a  msi installer

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As an add-on to the other answers  here s how I d explain it to a layman   Your source code is like the blueprint of a ship  It defines how the ship should be made   If you hand off your blueprint to the shipyard  and they find a defect while building the ship  they ll stop building and report it to you immediately  before the ship has ever left the drydock or touched water  This is a compile-time error  The ship was never even actually floating or using its engines  The error was found because it prevented the ship even being made    When your code compiles  it s like the ship being completed  Built and ready to go  When you execute your code  that s like launching the ship on a voyage  The passengers are boarded  the engines are running and the hull is on the water  so this is runtime  If your ship has a fatal flaw that sinks it on its maiden voyage  or maybe some voyage after for extra headaches  then it suffered a runtime error

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here s a very simple answer   Runtime and compile time are programming terms that refer to different stages of software program development  In order to create a program  a developer first writes source code  which defines how the program will function  Small programs may only contain a few hundred lines of source code  while large programs may contain hundreds of thousands of lines of source code  The source code must be compiled into machine code in order to become and executable program  This compilation process is referred to as compile time  think of a compiler as a translator   A compiled program can be opened and run by a user  When an application is running  it is called runtime   The terms  runtime  and  compile time  are often used by programmers to refer to different types of errors  A compile time error is a problem such as a syntax error or missing file reference that prevents the program from successfully compiling  The compiler produces compile time errors and usually indicates what line of the source code is causing the problem   If a program s source code has already been compiled into an executable program  it may still have bugs that occur while the program is running  Examples include features that don t work  unexpected program behavior  or program crashes  These types of problems are called runtime errors since they occur at runtime   The reference

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Following from previous similar answer of question What is the difference between run-time error and compiler error     Compilation Compile time Syntax Semantic errors  Compilation or compile time errors are error occurred due to typing mistake  if we do not follow the proper syntax and semantics of any programming language then compile time errors are thrown by the compiler  They wont let your program to execute a single line until you remove all the syntax errors or until you debug the compile time errors  Example  Missing a semicolon in C or mistyping int as Int   Runtime errors  Runtime errors are the errors that are generated when the program is in running state  These types of errors will cause your program to behave unexpectedly or may even kill your program  They are often referred as Exceptions  Example  Suppose you are reading a file that doesn t exist  will result in a runtime error      Read more about all programming errors here

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we can classify these under different two broad groups static binding and dynamic binding  It is based on when the binding is done with the corresponding values  If the references are resolved at compile time  then it is static binding and if the references are resolved at runtime then it is dynamic binding  Static binding and dynamic binding also called as early binding and late binding  Sometimes they are also referred as static polymorphism and dynamic polymorphism   Joseph Kulandai

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The major difference between run-time and compile time is    If there are any syntax errors and type checks in your code then it throws compile time error  where-as run-time it checks after executing the code  For example    int a   1  int b   a 0   here first line doesn t have a semi-colon at the end---  compile time error after executing the program while performing operation b  result is infinite---  run-time error    Compile time doesn t look for output of functionality provided by your code  whereas run-time does

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Compile time  Time taken to convert the source code into a machine code so that it becomes an executable is called compile time   Run time  When an application is running  it is called run time   Compile time errors are those syntax errors  missing file reference errors   Runtime errors happen after the source code has been compiled into an executable program and while the program is running  Examples are program crashes  unexpected program behavior or features don t work

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edit  the following applies to C  and similar  strongly-typed programming languages  I m not sure if this helps you    For example  the following error will be detected by the compiler  at compile time  before you run a program and will result in a compilation error   int i    string   -- gt  error at compile-time   On the other hand  an error like the following can not be detected by the compiler  You will receive an error exception at run-time  when the program is run    Hashtable ht   new Hashtable    ht Add  key    string       the compiler does not know what is stored in the hashtable    under the key  key  int i    int ht  key        -- gt  exception at run-time

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The difference between compile time and run time is an example of what pointy-headed theorists call the phase distinction   It is one of the hardest concepts to learn  especially for people without much background in programming languages   To approach this problem  I find it helpful to ask   What invariants does the program satisfy  What can go wrong in this phase  If the phase succeeds  what are the postconditions  what do we know   What are the inputs and outputs  if any    Compile time   The program need not satisfy any invariants   In fact  it needn t be a well-formed program at all   You could feed this HTML to the compiler and watch it barf    What can go wrong at compile time    Syntax errors Typechecking errors  Rarely  compiler crashes  If the compiler succeeds  what do we know    The program was well formed---a meaningful program in whatever language  It s possible to start running the program    The program might fail immediately  but at least we can try    What are the inputs and outputs    Input was the program being compiled  plus any header files  interfaces  libraries  or other voodoo that it needed to import in order to get compiled  Output is hopefully assembly code or relocatable object code or even an executable program   Or if something goes wrong  output is a bunch of error messages     Run time   We know nothing about the program s invariants---they are whatever the programmer put in   Run-time invariants are rarely enforced by the compiler alone  it needs help from the programmer  What can go wrong are run-time errors    Division by zero Dereferencing a null pointer Running out of memory   Also there can be errors that are detected by the program itself    Trying to open a file that isn t there Trying find a web page and discovering that an alleged URL is not well formed  If run-time succeeds  the program finishes  or keeps going  without crashing  Inputs and outputs are entirely up to the programmer   Files  windows on the screen  network packets  jobs sent to the printer  you name it   If the program launches missiles  that s an output  and it happens only at run time  -

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You can understand the code compile structure from reading the actual code  Run-time structure are not clear unless you understand the pattern that was used

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Look into this example    public class Test        public static void main String   args            int   x new int -5    compile time no error         System out println x length            The above code is compiled successfully  there is no syntax error  it is perfectly valid  But at the run time  it throws following error   Exception in thread  main  java lang NegativeArraySizeException     at Test main Test java 5    Like when in compile time certain cases has been checked  after that run time certain cases has been checked once the program satisfies all the condition you will get an output  Otherwise  you will get compile time or run time error

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I think of it in terms of errors  and when they can be caught   Compile time   string my value   Console ReadLine    int i   my value    A string value can t be assigned a variable of type int  so the compiler knows for sure at compile time that this code has a problem  Run time   string my value   Console ReadLine    int i   int Parse my value     Here the outcome depends on what string was returned by ReadLine    Some values can be parsed to an int  others can t  This can only be determined at run time

[language-agnostic] Runtime vs. Compile time

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