An output validator is a program that is given the output of a submitted program, the corresponding input file and the answer file for that input, and then decides whether the output provided is a correct output for the given input file.
A validator program must be an application (executable or interpreted) capable of being invoked with a command line call. The details of this invocation are described below. The validator program has two ways of reporting back the results of validating:
- The validator must give a judgment (see Reporting a judgment).
- The validator may give additional feedback, e.g., an explanation of the judgment to humans (see Reporting Additional Feedback).
When invoked the output validator will be passed at least three command line parameters and the output stream to validate on stdin.
The validator should be possible to use as follows on the command line:
./validator input judge_answer feedback_dir [additional_arguments] < team_output [ > team_input ]
The meaning of the parameters listed above are:
- a string specifying the name of the input data ﬁle which was used to test the program whose results are being validated.
- a string specifying the name of an arbitrary “answer ﬁle” which acts as input to the validator program. The answer ﬁle may, but is not necessarily required to, contain the “correct answer” for the problem. For example, it might contain the output which was produced by a judge’s solution for the problem when run with input ﬁle as input. Alternatively, the “answer ﬁle” might contain information, in arbitrary format, which instructs the validator in some way about how to accomplish its task. The meaning of the contents of the answer ﬁle is not defined by this standard.
- a string which specifies the name of a “feedback directory” in which the validator can produce "feedback files" in order to report additional information on the validation of the output ﬁle. The feedbackdir must end with a path separator (typically '/' or '\' depending on operating system), so that simply appending a filename to feedbackdir gives the path to a file in the feedback directory.
- in case the problem specifies additional validator_flags, these are passed as additional arguments to the validator on the command line.
- the output produced by the program being validated is given on the validator's standard input pipe.
- when running the validator in interactive mode everything written on the validator's standard output pipe is given to the program being validated. Please note that when running interactive the program will only receive the output produced by the validator and will not have direct access to the input file.
The two files pointed to by input and judge_answer must exist (though they are allowed to be empty) and the validator program must be allowed to open them for reading. The directory pointed to by feedback_dir must also exist.
Reporting a judgment
A validator program is required to report its judgment by exiting with speciﬁc exit codes:
- If the output is a correct output for the input ﬁle (i.e., the submission that produced the output is to be Accepted), the validator exits with exit code 42.
- If the output is incorrect (i.e., the submission that produced the output is to be judged as Wrong Answer), the validator exits with exit code 43.
Any other exit code (including 0!) indicates that the validator did not operate properly, and the contest control system invoking the validator must take measures to report this to contest personnel. The purpose of these somewhat exotic exit codes is to avoid conﬂict with other exit codes that results when the validator crashes. For instance, if the validator is written in Java, any unhandled exception results in the program crashing with an exit code of 1, making it unsuitable to assign a judgment meaning to this exit code.
Reporting Additional Feedback
The purpose of the feedback directory is to allow the validator program to report more information to the contest control system than just the accept/reject verdict. Using the feedback directory is optional for a validator program, so if one just wants to write a bare-bones minimal validator, it can be ignored.
The validator is free to create different files in the feedback directory, in order to provide different kinds of information to the contest control system, in a simple but organized way. For instance, there may be a “judgemessage.txt” file, the contents of which gives a message that is presented to a judge reviewing the current submission (typically used to help the judge verify why the submission was judged as incorrect, by specifying exactly what was wrong with its output). Other examples of files that may be useful in some contexts (though not in the ICPC) are a score.txt file, giving the submission a score based on other factors than correctness, or a teammessage.txt file, giving a message to the team that submitted the solution, providing additional feedback on the submission.
A contest control system that implements this standard must support the judgemessage.txt file described above (I.e., content of the "judgemessage.txt" file, if produced by the validator, must be provided by the contest control system to a human judge examining the submission). Having the Contest Control System support other files is optional.
Note that a validator may choose to ignore the feedback directory entirely. In particular, the contest control system must not assume that the validator program creates any files there at all.
An example of a judgemessage.txt file:
Team failed at test case 14. Team output: "31", Judge answer: "30". Team failed at test case 18. Team output: "hovercraft", Judge answer: "7". Summary: 2 test cases failed.
An example of a teammessage.txt file:
Almost all test cases failed, are you even trying to solve the problem?
Validator standard output and standard error
A valididator program is allowed to write any kind of debug information to its standard error pipe. This information may be displayed to the user upon invocation of the validator.