Both Winston Smith and Victor Frankl end up imprisoned by a totalitarian state in a dehumanizing situation meant to break their spirits. Frankl ended up in Auschwitz for the "crime" of being Jewish, and Winston ended up in the Ministry of Love for conspiring against Oceania and the Party.
Both are sympathetic characters caught up in unjust situations. Both are also sustained by thoughts of their beloved. Winston, for example, believes that no matter how much O'Brien tortures him and no matter what he confesses to or says, he will never lose his humanity because he will never betray Julia. Winston takes comfort in the fact that:
he had not betrayed her. He had not stopped loving her; his feelings towards her had remained the same
Frankl is also sustained by thought of his beloved, in his case, his wife. He dreams of the time they can meet again when they war is over and these thoughts comfort him:
I did not know whether my wife was alive, and I had no means of finding out ... but at that moment it ceased to matter. There was no need for me to know; nothing could touch the strength of my love, my thoughts, and the image of my beloved.
While both are sustained by their love for another person, a key difference is that Frankl never betrays his beloved. On the other hand, when faced with his worse fear—having his face eaten alive by a giant, hungry rat—Winston betrays Julia, crying out for this to be done to her, not him.
Other differences between the two is the isolation of Winston compared to Frankl. Winston seldom sees other prisoners and when he does, it is for brief moments. His main interactions are with O'Brien, his torturer. Frankl, in contrast, lives in community with other prisoners. It is a debased community, but he nevertheless has the companionship of others in the same situation. He is also helped through community; for example, he is liked by a certain guard who makes life easier for him.
While deprived of community, however, Winston is privy (through O'Brien) to the thinking, plans, and rationale of the state of Oceania, learning for example, that the state's vision of the future is, as O'Brien describes it:
a boot stamping on a human face—for ever
In contrast, one of the fundamental difficulties Frankl and the other prisoners face is a lack of any answer to the question of why they are there and what their purpose is, leading Frankl to conclude that a sense of purpose and meaning is foundational to life itself.