The vast majority of the time, 1 and 1 openings show hands with a real club or diamond suit. Normally we open with one of our longest suit (or 1NT with the appropriate strength and distribution). The only time a problem occurs is when our longest suit is a 4-card major, and we have the wrong strength to open 1NT.
That means there are only four possible problem distributions:
In Standard American, hands 1, 2, and 3 are opened 1, and hand 4 is opened 1. (Always open 1 with 3-3 in the minors.) This style is often called "convenient minor." Some partnerships agree instead to open "better minor" and open hand 1 with 1. Others agree to play a "short club" open all four of these hands with 1.
Outside of North America, bidding a 3-card suit is commonly called a prepared minor opening, because this bid is made in preparation for a easy rebid:
Now, let's go across to the other side of the table, and see whether we need to worry about partner having his suit or not:
If partner rebids his suit, he normally has at least six cards. 1-1-2 and 1-1-2 absolutely promise six cards. 1-1-2 could be a strong 5-card suit. If opener has a minimum 3-1-4-5 or 3-4-1-5, he has to choose between raising spades with three or rebidding clubs with five.
If partner bids a second suit at the 2-level, his first suit is always real, and almost always 5+ cards long. 1-1-2 almost guarantees five diamonds and four clubs. 1-1-2 might be a 1-4-4-4 hand.
Opener's reverse shows extra strength, and promises his first suit is longer than his second.
If opener bids one minor and raises the other, he really has both of them. His raise promises 4-card support, and with you'd never open a 3-card minor if you had 4 of the other. If the bidding goes 1-2-3, opener has at least four of each. After 1-1-2, opener likely has 5 clubs and 4 diamonds: a balanced hand might have bid notrump.
If opener raises responder's major, you'll be playing in responder's major suit. After 1-1-2, opener may or may not have a club suit, but it doesn't matter, since the final contract will never be in clubs. (A 3 bid by responder now would ask opener to choose between partscore and game in spades according to how good his clubs are -- it's not an offer play in clubs.)
If opener rebids NT and responder has a balanced hand, you'll be playing in NT. If responder has KJ86 AQ6 K832 J8 and the auction goes 1-1-1NT-3NT, opener might be 3-4-3-3 or 2-3-3-5, but you'd want to be in 3NT either way.
You should still usually assume opener has a real suit unless he tells you otherwise. For instance, suppose you hold KQ965 K73 2 J752. Partner opens 1, you respond 1, partner rebids 1NT. Your next bid should be 2 whether opener has a real club suit or not. Opener will choose between clubs and spades - and if he opened a 3-card club suit, he has to have at least three spades, and will now bid 2.
The one "dangerous" auction, 1-2 / 1-2, is rare. Responder will only raise opener to two if he doesn't have a 4-card major and he has an unbalanced hand and isn't willing to bid 1NT -- this means reponder almost always has 5-card support for this raise.
In summary, if opener