اشاره گر به تابع 5/23/2016

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$com * date: 1395/03/03 */ int main() { cout<< "In the name of God"; Lecture_25 (); return 0; string Lecture_25() { cout << Pointers to functions" <<endl; cout << STL: Standard Template Library"$

1 /* * advanced programming * Alireza Akhavan Pour * akhavan@alirezaweb.com * date: 1395/03/03 */ int main() { cout<< "In the name of God"; Lecture_25 (); return 0; string Lecture_25() { cout << Pointers to functions" <<endl; cout << STL: Standard Template Library" <<endl; return ":)"; 1 اشاره گر به تابع اشاره گر به تابعی که یک int میگیرد و چیزی برنمیگرداند در اینجا تابع print فراخوانی میشود چون در خط قبل آدرس آن در اشارهگر قرار داده شده است. می توان مقدار اشاره گر را عوض کرد و آدرس تابع دیگری را در آن گذاشت 01-FuncPtr.cpp 2 1

2 تعریف تایپ برای اشاره گر به توابع func_ptr_type نام تایپ اشارهگر به توابعی است که یک int میگیرد و چیزی برنمیگرداند fp اشارهگری از نوع func_ptr_type است 02-FuncPtrTypedef.cpp 3 رد کردن توابع به عنوان پارامتر( با ( typedef در این مثال تابعی تعریف می شود که پارامتر آن توابع هستند. پارامتر اول این تابع تابعی است که دو عدد می گرد و یک عدد برمی گرداند معادل با add(add(1,3),5) معادل با sub(sub(1,3),5) 03-FuncPtrParam.cpp 4 2

3 04-FuncPtrParam.cpp 5 STL Standard Template Library 6 3

4 Common tasks Collect data into containers Organize data For printing For fast access Retrieve data items By index (e.g., get the Nth element) By value (e.g., get the first element with the value "Chocolate") By properties (e.g., get the first elements where age<64 ) Add data Remove data Sorting and searching Simple numeric operations 7 Observation We can (already) write programs that are very similar independent of the data type used Using an int isn t that different from using a double Using a vector<int> isn t that different from using a vector<string> 8 4

5 Ideals We d like to write common programming tasks so that we don t have to re-do the work each time we find a new way of storing the data or a slightly different way of interpreting the data Finding a value in a vector isn t all that different from finding a value in a list or an array Looking for a string ignoring case isn t all that different from looking at a string not ignoring case Graphing experimental data with exact values isn t all that different from graphing data with rounded values Copying a file isn t all that different from copying a vector ایده آل اینه که کارهای برنامه نویسیمون را جوری بنویسیم که الزم نباشه هی تکرار کنیم 9 Ideals (continued) Code that s Easy to read Easy to modify Regular Short Fast Uniform access to data Independently of how it is stored Independently of its type 10 5

6 Ideals (continued) Type-safe access to data Easy traversal of data Compact storage of data Fast Retrieval of data Addition of data Deletion of data Standard versions of the most common algorithms Copy, find, search, sort, sum, 11 Examples Sort a vector of strings Find an number in a phone book, given a name Find the highest temperature Find all values larger than 800 Find the first occurrence of the value 17 Sort the telemetry records by unit number Sort the telemetry records by time stamp Find the first value larger than Petersen? What is the largest amount seen? Find the first difference between two sequences Compute the pairwise product of the elements of two sequences What are the highest temperatures for each day in a month? What are the top 10 best-sellers? What s the entry for C++ (say, in Google)? What s the sum of the elements? کارهایی که میخوایم انجام بدیم از تنوع زیادی برخوردار هستند. کل این اسالید هدفش اینه که بگه generic کردنه کار آسونی نیست! ممکنه بخواهیم با داشتن یه اسم شماره تلفن یه فرد را تو دفترچه تلفن پیدا کنیم یا اعداد بزرگتر از 17 را بیایم یا 10 عدد بزرگتر و... چه قدر میشه generic بنویسم که راحت بشه این کارا را انجام داد 12 6

7 Generic programming Generalize algorithms Sometimes called lifting an algorithm The aim (for the end user) is Increased correctness Through better specification Greater range of uses Possibilities for re-use Better performance Through wider use of tuned libraries Unnecessarily slow code will eventually be thrown away Go from the concrete to the more abstract The other way most often leads to bloat چه طوری کدی را که داریم generic بکنیم اصطالحی ک به کار میبره liftingه یعنی کدمان را تو سطوح انتزاع یه lift کنم باال که تو سطح abstractتری کار کنه هدف اینه که: اوال correctness باال باشه خطا و باگ پیش نیاد وسعت استفاده باال باشه پرفورمنس خوبی داشته باشیم 13 Lifting example (concrete algorithms) double sum(double array[], int n) { double s = 0; for (int i = 0; i < n; ++i ) s = s + array[i]; return s; struct Node { Node* next; int data; ; // one concrete algorithm (doubles in array) Concrete!= Abstract دو ورژن از تابع sum که یکی روی آرایه ای از double کار میکند و دیگری روی لیست پیوندی از. int الگوریتم ها abstract نیستند و فقط روی همون ساختمان داده کار میکنند اما کارهای تکراری دیده میشه! int sum(node* first) { int s = 0; while (first) { s += first->data; first = first->next; return s; // another concrete algorithm (ints in list) // terminates when expression is false or zero 14 7

8 Lifting example (abstract the data structure) // pseudo-code for a more general version of both algorithms int sum(data) // somehow parameterize with the data structure { int s = 0; // initialize while (not at end) { // loop through all elements s = s + get value; // compute sum get next data element; return s; // return result We need three operations (on the data structure): not at end get value get next data element 15 The STL Part of the ISO C++ Standard Library Mostly non-numerical Only 4 standard algorithms specifically do computation Accumulate, inner_product, partial_sum, adjacent_difference Handles textual data as well as numeric data E.g. string Deals with organization of code and data Built-in types, user-defined types, and data structures Optimizing disk access was among its original uses Performance was always a key concern 16 8

The STL Designed by Alex Stepanov General aim: The most general, most efficient, most flexible representation of concepts (ideas, algorithms) Represent separate concepts separately in code Combine

9 The STL Designed by Alex Stepanov General aim: The most general, most efficient, most flexible representation of concepts (ideas, algorithms) Represent separate concepts separately in code Combine concepts freely wherever meaningful General aim to make programming like math or even Good programming is math works for integers, for floating-point numbers, for polynomials, for 17 Lifting example (STL version) // Concrete STL-style code for a more general version of both algorithms template<typename Iter, class T> // Iter should be an Input_iterator // T should be something we can + and = T sum(iter first, Iter last, T s) // T is the accumulator type { while (first!=last) { s = s + *first; ++first; return s; Let the user initialize the accumulator float a[] = { 1,2,3,4,5,6,7,8 ; double d = 0; d = sum(a,a+sizeof(a)/sizeof(*a),d); 18 9

10 Basic model Algorithms sort, find, search, copy, Containers iterators vector, list, map, unordered_map, Separation of concerns Algorithms manipulate data, but don t know about containers Containers store data, but don t know about algorithms Algorithms and containers interact through iterators Each container has its own iterator types 19 The STL An ISO C++ standard framework of about 10 containers and about 60 algorithms connected by iterators Other organizations provide more containers and algorithms in the style of the STL Boost.org, Microsoft, SGI, Probably the currently best known and most widely used example of generic programming 20 10

11 Basic model A pair of iterators defines a sequence The beginning (points to the first element if any) The end (points to the one-beyond-the-last element) begin: end: An iterator is a type that supports the iterator operations ++ Go to next element * Get value == Does this iterator point to the same element as that iterator? Some iterators support more operations (e.g. --, +, and [ ]) 21 vector Containers (hold sequences in difference ways) list (doubly linked) set (a kind of tree)

Basic iterator usage begin: end: it: فرض میشود همه کالسها کالسی به نام iteratorداخل خودشان دارند و متدهایی به نامهای begin و endرا پیاده سازی کردند که هر

12 Basic iterator usage begin: end: it: فرض میشود همه کالسها کالسی به نام iteratorداخل خودشان دارند و متدهایی به نامهای begin و endرا پیاده سازی کردند که هر کدام از این متدها در کالس اصلی یک iterator به اولین عنصر و عنصر بعد از آخری را بر میگردانند. 05_VectorIterator.cpp 23 مثال اسالید شماره genericSum.cpp 24 12

13 منابع pointers to functions: STL:

مرتب سازی. (sort) : ویرایش احمدرضا غدیرزاده دانشجوی رشته ی مهندسی کامپیوتر

مرتب سازی. (sort) : ویرایش احمدرضا غدیرزاده دانشجوی رشته ی مهندسی کامپیوتر مرتب سازی (sort) : ویرایش احمدرضا غدیرزاده دانشجوی رشته ی مهندسی کامپیوتر تعریف کلید بخشی از هر رکورد که مرتبسازی بر اساس آن انجام میگیرد. به طور کلی الگوریتمهای مرتبسازی را میتوان به دو گروه تقسیم کرد: