randline — print a random line from stdin

Copyright (c) 2018 Bart Massey

This code is supposed to be a simple but correct C implementation of the spec "read stdin, which is assumed to be 8-bit "ASCII" text, and print a random line on stdout."

No real effort has been made to make the code efficient in either time or space.

The program is expected to tolerate all valid ASCII inputs.

• It is permitted to run out of memory if necessary, in which case it will fail and dump core.

• It is permitted to fail and exit with an error message if an underlying library routine fails.

• It is permitted to exit with an error message if the file contains ASCII NUL characters ('\0') since there is no reasonable way to represent them as a C string.

• It is required to pass all 8-bit characters other than NUL through unchanged. This should make it work with UTF-8 strings.

• It is required to produce a line uniform-randomly from the file, upt to limitations of implementations of the ANSI rand() and srand() functions.

The algorithm chosen is the naïve one which stores every line in a file

The motivation here, other than as a coding exercise, is to show how unbelievably hard and error-prone it is to code this correctly in C.

The C code contains extensive comments to try to explain what is going on.

Implementations in C++, Rust, Haskell and Python are provided for comparison and contrast. These implementations may fail with errors if the input is not valid UTF-8, which may or may not be a feature.

This program is licensed under the "MIT License". Please see the file LICENSE in the source distribution of this software for license terms.