What is the difference between logic error and runtime error?

[charlesesl]

In both cases the program will run. So how do I differentiate between the two types of errors.

[kel]

Logic errors and run-time errors are sort of the same thing.

They both occur at runtime. A logic error means you accidentally expressed something that you didn't mean to express, or you expressed something that is logically incorrect and will produce undesirable results.

A run-time error can be produced by a logic error, I would say there are two types of runtime errors fatal, and non-fatal, a fatal error crashes the program, and non-fatal error (usually logic) returns incorrect results.

Run-time errors also encompass incorrect use of libraries and other bugs that might cause unexpected behavior.

I think Logic error usually is meant to specify that it is the fault of the programmer and not the machine or underlying system.

[bogosj13]

Runtime errors can basically occur for two reasons.

1) Something completely out of your control during implementation

Attempting to read from a socket that got closed, trying to read a file that was deleted from disk, or a set of dependant libraries being removed can all cause runtime errors.

2) Not properly checking input from users.

One of the classic examples is when doing database work. If you forget to properly translate strings passed to your code (or you don't use the right functions), and a user inputs the string:

Bob's Birthday

The single quote can totally screw up your SQL statement.

Logic errors, on the other hand, are much more dangerous (in my opinion). This is because a logic error can sometimes go unnoticed for a long time. If a user is using the system to input data, and the data gets manipulated and stored, it's entirely possible that a logic error is causing the data to be stored incorrectly. As far as the user can tell, the data gets into the system, because no big error box tells them otherwise. This can cause serious latent issues in stored data.

[kel]

... bogosj13 is right, that's the difference, it's not something I usually think about.

[Latch]

This sounds like a homework question hehe.

[Rangsk]

This sounds almost exactly like a midterm/final question I had in an early CS class. I believe this is the kind of answer your professor (I'm guessing this is for a class) is looking for:

A logic error is when the program runs fine and does not crash, however it does not run the way it should because the programmer did not program what he or she intended to program. For example, a loop that loops an incorrect number of times would be a logic error.

A runtime error is something not picked up by the compiler at compile time, but is reported by the OS while the program is running. The most frequent runtime errors are reading a null pointer, stack overflows, segmentation fauilts, and unhandled exceptions. Runtime errors will always cause the program to exit immediately.

[bogosj13]

Originally posted by Rangsk
... Runtime errors will always cause the program to exit immediately. [/B]

That is unless you are using a language that supports handling exceptions (which most all do). Properly writing code to handle runtime exceptions perfectly is hard, but getting 99% of them is usually good enough.

Java has try {} catch {}, so does C# and C++ I believe. VB has the "On Error Goto" mess, but I guess it's better than nothing.

[Pragma]

Just to confirm: C++ and C# do have try/catch exception handling.