Chapter 1
C++ Templates
Sections 1.6 and 1.7
1
Templates
• Type-independent patterns that can work with
multiple data types
– Generic programming
– Code reusable
• Function Templates
– These define logic behind the algorithms that work for
multiple data types
• Class Templates
– These define generic class patterns into which specific data
types can be plugged in to produce new classes
2
Function Templates
• Algorithms may use the same logic for different data
types
– Different definitions are written just to deal with different
data types
– Templates permit a common code, independent of the data
type
– Templates should be in header files, so that the compiler
will know how to generate code when it sees the template
used
• Examples
– Lec4/
largest.h/cpp, uselargest.cpp
Error with template in the .cpp file
$ g++ uselargest.cpp largest.cpp
/tmp/ccAg3qmY.o: In function `main':
uselargest.cpp:(.text+0x133): undefined reference to `int
tlargest<int>(int*, int)'
uselargest.cpp:(.text+0x16c): undefined reference to `float
tlargest<float>(float*, int)'
3
Class Templates
• Identical code can be used for classes that have
data of different types
• Examples
– Lec4/ pair.h, usepair.cpp
– Use friend function to access private members (example,
for IO)
• The approach used in the text is also ok
– Note the use of a space between > and > in usepair.cpp
• This makes the compiler realize that >> is not a single
token
4
An Alternative to friend
• Use a public ‘print’ function
and an operator that calls it
5
STL Containers
• Container: stores other objects
– Common operations such as: push_back, back, front, [ ],
etc
• Not all operations are defined for all containers
– Sequence: positions of elements are important
• Example: vector, list
– Associative containers: elements are accessed through
keys
• Example: map, set, pair
• Example
– Lec4/vlm.cpp for example with vector, list, and map
6
STL Iterators
• Iterator: like a pointer to elements of a container
– Used to access elements of a container
– Popular operators
• * (dereference), ++, --, ==, !=
– Examining all the elements of a container
• c.begin() returns an iterator to the first element of
container c
• c.end returns a pointer to one past the end
7
Matrices
• C++ library does not
provide a matrix class
• Constructor
– Creates rows number of
zero-sized vectors
– Resizes each vector to col
elements
• Two types of [ ] operators
– One for LHS that returns
by reference
– Another for RHS that
returns by constant
reference
• to[i] = from[i]
– So we have two very
identical functions
• What makes their
signatures different?
8