Runtime vs Compile time

Question

Can anyone please give me a good understanding of whats the difference between run-time and compile-time?

Answer 1

(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"; --> 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"];  // --> exception at run-time

Answer 2

Run time means something happens when you run the program.

Compile time means something happens when you compile the program.

Answer 3

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:

Answer 4

Apart from what it is said above I want to add that sometimes a picture worth 1000 words :

1. 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

2. search on google and compare runtime errors vs compile errors:

;

3. 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.

Answer 5

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

1. What invariants does the program satisfy?
2. What can go wrong in this phase?
3. If the phase succeeds, what are the postconditions (what do we know)?
4. What are the inputs and outputs, if any?

Compile time

1. 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...
2. What can go wrong at compile time:
   • Syntax errors
   • Typechecking errors
   • (Rarely) compiler crashes
3. 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.)
4. 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

1. 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.

2. 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
3. If run-time succeeds, the program finishes (or keeps going) without crashing.
4. 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 :-)

Answer 6

In simply word difference b/w Compile time & Run time.

compile time:Developer writes the program in .java format & 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 & the logic turns out be wrong and throws an error which is a run time error