In computer programming, a return code or an error code is a numeric or alphanumeric code that is used to determine the nature of an error and why it occurred. They are also commonly found in consumer electronics and devices when they attempt to do something they cannot do (e.g., dividing by zero) or fail to do and they can be passed off to error handlers that determine what action to take.
Error codes can also be used to specify an error, and simplify research into the cause and how to fix it. This is commonly used in consumer products when something goes wrong, such as the cause of a Blue Screen of Death, to make it easier to pinpoint the exact problem the product is having.
There is no definitive form of an error code. Some styles use decimal or hexadecimal numbers, others use alphanumeric codes and some use a phrase describing the error.
Error codes in computers can be passed to the system itself, to judge how to respond to the error. Often error codes come synonymous with an exit code or a return value. The system may also choose to pass the error code to its user(s). The Blue screen of death is an example of how a popular operating system communicates error codes to the user.
Error codes are passed to exception handling in programming languages that support it. These are passed to log files and the parent process to determine what action to take.