Changes needed for the melodic and harmonic versions of the scale are written in with accidentals as necessary. The C-sharp harmonic minor and melodic minor scales are:
Its relative major is E major. Its parallel major, C-sharp major, is usually written instead as the enharmonic key of D-flat major, since C-sharp major’s key signature with seven sharps is not normally used. Its enharmonic equivalent, D-flat minor, having eight flats including the B, has a similar problem. Therefore, C-sharp minor is often used as the parallel minor for D-flat major. (The same enharmonic situation occurs with the keys of A-flat major and G-sharp minor, and in some cases, with the keys of G-flat major and F-sharp minor.)
There are only two known symphonies in the 18th century written in this key. One of them is by Joseph Martin Kraus, who appears to have found the key difficult since he later rewrote it in C minor. In the following two centuries, C-sharp minor symphonies remained rare. Notable examples are the second movement Adagio of Anton Bruckner's Symphony No. 7, the first movement of Gustav Mahler's Symphony No. 5[1] and Prokofiev's Symphony No. 7.
^Constantin Floros, translated by Vernon Wicker: Gustav Mahler: The Symphonies (Portland, Oregon: Amadeus Press, 1985) p. 141 "the choice of key of the movements (C-sharp minor – A minor – D major – F major – D major);" - however, Mahler did not apply any key to the 5th symphony as a whole