Friday, April 14, 2006

Really short STL notes

My STL notes after reading Effective STL by Scott Meyer. For most of the points below, there are subtle important reasons for that. The reasons are not mentioned here as it would be too long. Please read Effective C++ by Scott Meyer.

1. Use member insert function instead of copy algorithm and inserter.

2. Minimize capacity: string (s).swap (s)
Clear and minimize capacity : string ().swap (s)

3. Associative containers use equivalence (strict weak ordering) and not equality.
Equivalence: !(w1 < w2) && !(w2 > w1)
In strict weak ordering, equal values are not equivalent!
Therefore, Comparison function should return false for equal values when equivalence is expected.

4. Use map::operator [] to modify/retrieve existing elements in the map
Use map::insert to add new elements

5. Iterator can be implicitely converted to reverse_iterator.
reverse_iterator to iterator: use member base() function.
const_cast works for conversion from const_iterator to iterator of strings and vector because they are char* and T* pointers. For others to convert from const_iterator to iterator use std::advance (i, distance (i,ci))

6. istream_iterator is used for formatted input. (does not read spaces)
istreambuf_iterator also reads spaces between strings.

7. v.reserve(size) does not invoke constructor (even default). It simply allocates more memory, if any, to hold size objects. Insertion of value at v.end () is wrong in general, use back_inserter (v) instead. Insertion is important and not assignment even after reserve.

8. v.remove () may not erase elements from the container, therefore, v.size() may not change after v.remove.

9. binary_search should receive same comparison function as the sort function did.

10. Custom function objects should be adaptable. To make them adaptable inherit from unary_function or binary_function. Adaptable function objects can be used with not1.
ptr_fun, mem_fun and mem_fun_ref are used to adapt member functions for algorithms like for_each.

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