Definition of "extern"

Heaven is my judge, not I for love and duty, / But seeming so, for my particular end, / For when my outward action doth demonstrate / The native act and figure of my heart / In complement extern, 'tis not long after / But I will wear my heart upon my sleeve / For daws to peck at.

c. 1603–1604 (date written), William Shakespeare, “The Tragedie of Othello, the Moore of Venice”, in Mr. William Shakespeares Comedies, Histories, & Tragedies […] (First Folio), London: […] Isaac Iaggard, and Ed[ward] Blount, published 1623, [Act I, scene i]

For if the ſoul of man vvere emancipated by virtue, it vvould not need any regulation or monition, beſides that of its invvard Tribunal; vvhich becauſe ſin does uſurp upon, has ſome relief from thoſe extern adjuments.

1663, Edward Waterhous [i.e., Edward Waterhouse], chapter XIV, in Fortescutus Illustratus; or A Commentary on that Nervous Treatise De Laudibus Legum Angliæ, Written by Sir John Fortescue Knight, […], London: […] Tho[mas] Roycroft for Thomas Dicas […], page 214

Finally, get rid of the two function declarations and two externs that we added at the top of TEFIL.CPP so that we could support file_open().

1995, Martin L. Rinehart, Learn C++ Today!, page 552

This is probably the big thing with C++, the more you can avoid global concepts and nasty externs the better, an object/class should be totally self-contained.

2018, Brian Beuken, The Fundamentals of C/C++ Game Programming