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Standard Template Library. C++ introduced both object-oriented ideas, as well as templates to C Templates are ways to write general code around objects or types to be declared by the programmer sort, find, sets, looping. Why Templates. void swap(int& a, int& b) { int temp = a; - PowerPoint PPT Presentation
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Standard Template Library
C++ introduced both object-oriented ideas, as well as templates to CTemplates are ways to write general code around objects or types to be declared by the programmer sort, find, sets, looping
Why Templates
void swap(int& a, int& b) { int temp = a; a = b; b = temp;}
Templates allow common logic with different data types
template <class C>void swap(C& a, C& b) { C temp = a; a = b; b = temp;}
STL Example
vector<int> v(3); // Declare a vector of 3 elements. v[0] = 7; v[1] = v[0] + 3; v[2] = v[0] + v[1];
reverse(v.begin(), v.end());
Advantages of using templated containers
Common code can be written just once with basic data structuresAlgorithms on basic structures can be implemented generally (and efficiently)Standard data processing tasks can be reduced to calls to the standard template library allows programmer to focus on value-
add parts of code
Comparison to Java
In Java, general classes like Vector and List can be programmedNot typed: any object can be put in a vector leads to possible errors in the code
No optimization possible based on type knowing both the container and data type at
compile time, the best-suited algorithm can be chosen
Data structures/containers
Vectors
set
lists
dequeue
Hashes (map in STL)
Less known than other containersWork like instant telephone book lookups, or a generic arrayInput and Output can be of any type e.g. string -> phone number
Access is very fast: log(n) on average
Map example
Counting number of occurrences of each string
#include <map>#include <string>#include <iostream>
using namespace std;
int main() { map <string, int> string_count; string word; // input buffer for words.
//--- Read words/tokens from input stream cout << "Enter words, pressing enter in between. Press <ctrl>-D to end." << endl; while (cin >> word) { string_count[word]++; }
//--- Write the count and the word. cout << " --- Word counts ---" << endl; map<string, int>::const_iterator iter; for (iter=string_count.begin(); iter != string_count.end(); ++iter) { cout << iter->second << " " << iter->first << endl; } return 0;}//end main
Functions on standard objects
Data structures aren't much good without functions that work on themGeneric algorithms can often take any flavour of container sorting works on vectors, lists, queues
particular algorithm will take advantage of appropriate aspects of container sorting vectors is faster than sorting
linked lists
Types of STL AlgorithmsNon-Mutating for_each find find_if adjacent_find find_first_of count count_if mismatch equal
Mutating sort copy transform replace fill generate reverse random_shuffl
e partition
Memory Management
Typing allows templated functions to be efficient (almost always better than hand-written functions)Surprisingly easy to manage memory
Vector Memory Optinsvoid myfunction () {vector<int> v1(100); // set size to 100
vector<int> v2(100);<..find out you need 200 elements>v2.resize(200); // now storage and size are 200
vector<int> v3;v3.reserve(100); // make room for 100, but size=0for (i = 1; i < 150; i++) { v3.push_back(i);}
}
In all cases, memory in vector is freed at end of function
Learning the STL
The standard template library is not the easiest thing to understandSimple examples cut+paste is definitely the way to startBest done after some C++ programming experience, reading template compiler errors are among the
most cryptic I've ever seen Need to be able to "think like a compiler" to
interpret them
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