C++ Input/Output: Streams 4
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CS 61A Streams Summer 2019 1 Streams
CS 61A Streams Summer 2019 Discussion 10: August 6, 2019 1 Streams In Python, we can use iterators to represent infinite sequences (for example, the generator for all natural numbers). However, Scheme does not support iterators. Let's see what happens when we try to use a Scheme list to represent an infinite sequence of natural numbers: scm> (define (naturals n) (cons n (naturals (+ n 1)))) naturals scm> (naturals 0) Error: maximum recursion depth exceeded Because cons is a regular procedure and both its operands must be evaluted before the pair is constructed, we cannot create an infinite sequence of integers using a Scheme list. Instead, our Scheme interpreter supports streams, which are lazy Scheme lists. The first element is represented explicitly, but the rest of the stream's elements are computed only when needed. Computing a value only when it's needed is also known as lazy evaluation. scm> (define (naturals n) (cons-stream n (naturals (+ n 1)))) naturals scm> (define nat (naturals 0)) nat scm> (car nat) 0 scm> (cdr nat) #[promise (not forced)] scm> (car (cdr-stream nat)) 1 scm> (car (cdr-stream (cdr-stream nat))) 2 We use the special form cons-stream to create a stream: (cons-stream <operand1> <operand2>) cons-stream is a special form because the second operand is not evaluated when evaluating the expression. To evaluate this expression, Scheme does the following: 1. Evaluate the first operand. 2. Construct a promise containing the second operand. 3. Return a pair containing the value of the first operand and the promise. 2 Streams To actually get the rest of the stream, we must call cdr-stream on it to force the promise to be evaluated. -
Chapter 2 Basics of Scanning And
Chapter 2 Basics of Scanning and Conventional Programming in Java In this chapter, we will introduce you to an initial set of Java features, the equivalent of which you should have seen in your CS-1 class; the separation of problem, representation, algorithm and program – four concepts you have probably seen in your CS-1 class; style rules with which you are probably familiar, and scanning - a general class of problems we see in both computer science and other fields. Each chapter is associated with an animating recorded PowerPoint presentation and a YouTube video created from the presentation. It is meant to be a transcript of the associated presentation that contains little graphics and thus can be read even on a small device. You should refer to the associated material if you feel the need for a different instruction medium. Also associated with each chapter is hyperlinked code examples presented here. References to previously presented code modules are links that can be traversed to remind you of the details. The resources for this chapter are: PowerPoint Presentation YouTube Video Code Examples Algorithms and Representation Four concepts we explicitly or implicitly encounter while programming are problems, representations, algorithms and programs. Programs, of course, are instructions executed by the computer. Problems are what we try to solve when we write programs. Usually we do not go directly from problems to programs. Two intermediate steps are creating algorithms and identifying representations. Algorithms are sequences of steps to solve problems. So are programs. Thus, all programs are algorithms but the reverse is not true. -
File I/O Stream Byte Stream
File I/O In Java, we can read data from files and also write data in files. We do this using streams. Java has many input and output streams that are used to read and write data. Same as a continuous flow of water is called water stream, in the same way input and output flow of data is called stream. Stream Java provides many input and output stream classes which are used to read and write. Streams are of two types. Byte Stream Character Stream Let's look at the two streams one by one. Byte Stream It is used in the input and output of byte. We do this with the help of different Byte stream classes. Two most commonly used Byte stream classes are FileInputStream and FileOutputStream. Some of the Byte stream classes are listed below. Byte Stream Description BufferedInputStream handles buffered input stream BufferedOutputStrea handles buffered output stream m FileInputStream used to read from a file FileOutputStream used to write to a file InputStream Abstract class that describe input stream OutputStream Abstract class that describe output stream Byte Stream Classes are in divided in two groups - InputStream Classes - These classes are subclasses of an abstract class, InputStream and they are used to read bytes from a source(file, memory or console). OutputStream Classes - These classes are subclasses of an abstract class, OutputStream and they are used to write bytes to a destination(file, memory or console). InputStream InputStream class is a base class of all the classes that are used to read bytes from a file, memory or console. -
Chapter 10 Streams Streams Text Files and Binary Files
Streams Chapter 10 • A stream is an object that enables the flow of File I/O data between a ppgrogram and some I/O device or file – If the data flows into a program, then the stream is called an input stream – If the dtdata flows out of a program, then the stream is called an output stream Copyright © 2012 Pearson Addison‐Wesley. All rights reserved. 10‐2 Streams Text Files and Binary Files • Input streams can flow from the kbkeyboar d or from a • Files that are designed to be read by human beings, file and that can be read or written with an editor are – StSystem. in is an itinput stream tha t connects to the called text files keyboard – Scanner keyy(y);board = new Scanner(System.in); Text files can also be called ASCII files because the data they contain uses an ASCII encoding scheme • Output streams can flow to a screen or to a file – An advantage of text files is that the are usually the same – System.out is an output stream that connects to the screen on all computers, so tha t they can move from one System.out.println("Output stream"); computer to another Copyright © 2012 Pearson Addison‐Wesley. All rights reserved. 10‐3 Copyright © 2012 Pearson Addison‐Wesley. All rights reserved. 10‐4 Text Files and Binary Files Writing to a Text File • Files tha t are didesigne d to be read by programs and • The class PrintWriter is a stream class that consist of a sequence of binary digits are called binary files that can be used to write to a text file – Binary files are designed to be read on the same type of – An object of the class PrintWriter has the computer and with the same programming language as the computer that created the file methods print and println – An advantage of binary files is that they are more efficient – These are similar to the System.out methods to process than text files of the same names, but are used for text file – Unlike most binary files, Java binary files have the advantage of being platform independent also output, not screen output Copyright © 2012 Pearson Addison‐Wesley. -
HP C Run-Time Library Reference Manual for Openvms Systems
HP C Run-Time Library Reference Manual for OpenVMS Systems Order Number: BA554-90014 June 2010 This manual describes the functions and macros in the HP C Run-Time Library for OpenVMS systems. Revision/Update Information: This manual supersedes the HP C Run-Time Library Reference Manual for OpenVMS Systems, Version 8.3 Software Version: OpenVMS Version 8.4 for Integrity servers OpenVMS Alpha Version 8.4 Hewlett-Packard Company Palo Alto, California © Copyright 2010 Hewlett-Packard Development Company, L.P. Confidential computer software. Valid license from HP required for possession, use or copying. Consistent with FAR 12.211 and 12.212, Commercial Computer Software, Computer Software Documentation, and Technical Data for Commercial Items are licensed to the U.S. Government under vendor’s standard commercial license. The information contained herein is subject to change without notice. The only warranties for HP products and services are set forth in the express warranty statements accompanying such products and services. Nothing herein should be construed as constituting an additional warranty. HP shall not be liable for technical or editorial errors or omissions contained herein. UNIX is a registered trademark of The Open Group. X/Open is a registered trademark of X/Open Company Ltd. in the UK and other countries. Intel and Itanium are trademarks or registered trademarks of Intel Corporation or its subsidiaries in the United States and other countries. Microsoft and Windows are US registered trademarks of Microsoft Corporation. Printed in the US ZK5763 The HP OpenVMS documentation set is available on CD-ROM. This document was prepared using DECdocument, Version 3.3-1b. -
Subtyping, Declaratively an Exercise in Mixed Induction and Coinduction
Subtyping, Declaratively An Exercise in Mixed Induction and Coinduction Nils Anders Danielsson and Thorsten Altenkirch University of Nottingham Abstract. It is natural to present subtyping for recursive types coin- ductively. However, Gapeyev, Levin and Pierce have noted that there is a problem with coinductive definitions of non-trivial transitive inference systems: they cannot be \declarative"|as opposed to \algorithmic" or syntax-directed|because coinductive inference systems with an explicit rule of transitivity are trivial. We propose a solution to this problem. By using mixed induction and coinduction we define an inference system for subtyping which combines the advantages of coinduction with the convenience of an explicit rule of transitivity. The definition uses coinduction for the structural rules, and induction for the rule of transitivity. We also discuss under what condi- tions this technique can be used when defining other inference systems. The developments presented in the paper have been mechanised using Agda, a dependently typed programming language and proof assistant. 1 Introduction Coinduction and corecursion are useful techniques for defining and reasoning about things which are potentially infinite, including streams and other (poten- tially) infinite data types (Coquand 1994; Gim´enez1996; Turner 2004), process congruences (Milner 1990), congruences for functional programs (Gordon 1999), closures (Milner and Tofte 1991), semantics for divergence of programs (Cousot and Cousot 1992; Hughes and Moran 1995; Leroy and Grall 2009; Nakata and Uustalu 2009), and subtyping relations for recursive types (Brandt and Henglein 1998; Gapeyev et al. 2002). However, the use of coinduction can lead to values which are \too infinite”. For instance, a non-trivial binary relation defined as a coinductive inference sys- tem cannot include the rule of transitivity, because a coinductive reading of transitivity would imply that every element is related to every other (to see this, build an infinite derivation consisting solely of uses of transitivity). -
L13 Streams and IO
Binghamton CS-220 University Spring 20162015 Includes & Streams 1 Binghamton CS-220 University Spring 20162015 C Pre-Processor C Program Pre-Processor Pre-processed C Program Header Files Header Files 2 Binghamton CS-220 University Spring 20162015 #include • Two flavors: • #include <abc.h> • Replace this line with the contents of file abc.h found in the system libraries • #include “xyz.h” • Replace this line with the contents of file xyz.h found in the current directory • Concept: Write code once, use it in many different programs • By convention, included files are called “header files” and have a “.h” file type 3 Binghamton CS-220 University Spring 20162015 Header (.h) files • May include any valid C code • may include further #includes • Typically small – only what you need to invoke “outside” functions • Function prototype declarations • Sometimes, data and/or type declarations • Typically, a header file describes a group of functions • “related” functions – e.g. functions which deal with Input and Output • Typically associated with a “.c” file with the same name • .c file contains function definitions – more later 4 Binghamton CS-220 University Spring 20162015 C Standard Library • Part of C itself • Definitions/Descriptions included in C standard • Available with every C compiler • Primarily, a set of C functions we all can use • Keep C language simple • Wrap complicated stuff in function definitions • We don’t need to know about the implementation of the complicated stuff • Full description of standard library available as reference • Programming in C, Appendix B 5 Binghamton CS-220 University Spring 20162015 Standard Input and Output • Need: #include <stdio.h> • Large list of input and output functions to: • Read and write from a “stream” • Open a file and make a stream • Close a file and remove the stream • Create, Rename, delete, or move files • Streams…. -
CS2043 - Unix Tools & Scripting Cornell University, Spring 20141
CS2043 - Unix Tools & Scripting Cornell University, Spring 20141 Instructor: Bruno Abrahao January 31, 2014 1 Slides evolved from previous versions by Hussam Abu-Libdeh and David Slater Instructor: Bruno Abrahao CS2043 - Unix Tools & Scripting Vim: Tip of the day! Line numbers Displays line number in Vim: :set nu Hides line number in Vim: :set nonu Goes to line number: :line number Instructor: Bruno Abrahao CS2043 - Unix Tools & Scripting Counting wc How many lines of code are in my new awesome program? How many words are in this document? Good for bragging rights Word, Character, Line, and Byte count with wc wc -l : count the number of lines wc -w : count the number of words wc -m : count the number of characters wc -c : count the number of bytes Instructor: Bruno Abrahao CS2043 - Unix Tools & Scripting Sorting sort Sorts the lines of a text file alphabetically. sort -ru file sorts the file in reverse order and deletes duplicate lines. sort -n -k 2 -t : file sorts the file numerically by using the second column, separated by a colon Example Consider a file (numbers.txt) with the numbers 1, 5, 8, 11, 62 each on a separate line, then: $ sort numbers.txt $ sort numbers.txt -n 1 1 11 5 5 8 62 11 8 62 Instructor: Bruno Abrahao CS2043 - Unix Tools & Scripting uniq uniq uniq file - Discards all but one of successive identical lines uniq -c file - Prints the number of successive identical lines next to each line Instructor: Bruno Abrahao CS2043 - Unix Tools & Scripting Character manipulation! The Translate Command tr [options] <char_list1> [char_list2] Translate or delete characters char lists are strings of characters By default, searches for characters in char list1 and replaces them with the ones that occupy the same position in char list2 Example: tr 'AEIOU' 'aeiou' - changes all capital vowels to lower case vowels Instructor: Bruno Abrahao CS2043 - Unix Tools & Scripting Pipes and redirection tr only receives input from standard input (stdin) i.e. -
Data-Trace Types for Distributed Stream Processing Systems
Data-Trace Types for Distributed Stream Processing Systems Konstantinos Mamouras Caleb Stanford Rajeev Alur Rice University, USA University of Pennsylvania, USA University of Pennsylvania, USA [email protected] [email protected] [email protected] Zachary G. Ives Val Tannen University of Pennsylvania, USA University of Pennsylvania, USA [email protected] [email protected] Abstract guaranteeing correct deployment, and (2) the throughput of Distributed architectures for efficient processing of stream- the automatically compiled distributed code is comparable ing data are increasingly critical to modern information pro- to that of hand-crafted distributed implementations. cessing systems. The goal of this paper is to develop type- CCS Concepts • Information systems → Data streams; based programming abstractions that facilitate correct and Stream management; • Theory of computation → Stream- efficient deployment of a logical specification of the desired ing models; • Software and its engineering → General computation on such architectures. In the proposed model, programming languages. each communication link has an associated type specifying tagged data items along with a dependency relation over tags Keywords distributed data stream processing, types that captures the logical partial ordering constraints over data items. The semantics of a (distributed) stream process- ACM Reference Format: ing system is then a function from input data traces to output Konstantinos Mamouras, Caleb Stanford, Rajeev Alur, Zachary data traces, where a data trace is an equivalence class of se- G. Ives, and Val Tannen. 2019. Data-Trace Types for Distributed quences of data items induced by the dependency relation. Stream Processing Systems. In Proceedings of the 40th ACM SIGPLAN Conference on Programming Language Design and Implementation This data-trace transduction model generalizes both acyclic (PLDI ’19), June 22–26, 2019, Phoenix, AZ, USA. -
Stream Computing Based Synchrophasor Application for Power Grids
Stream Computing Based Synchrophasor Application For Power Grids Jagabondhu Hazra Kaushik Das Deva P. Seetharam IBM Research, India IBM Research, India IBM Research, India [email protected] [email protected] [email protected] Amith Singhee IBM T J Watson Research Center, USA [email protected] ABSTRACT grid monitoring to identify and deal with faults before they develop This paper proposes an application of stream computing analytics into wide-spread disturbances. framework to high speed synchrophasor data for real time moni- In recent years, electric grids are undergoing dramatic changes toring and control of electric grid. High volume streaming syn- in the area of grid monitoring and control. Key factors behind chrophasor data from geographically distributed grid sensors (namely, such transformation includes tremendous progress in the areas of Phasor Measurement Units) are collected, synchronized, aggregated power electronics, sensing, control, computation and communi- when required and analyzed using a stream computing platform to cation technologies. For instant, conventional sensors (e.g. Re- estimate the grid stability in real time. This real time stability mon- mote Terminal Units) provide one measurement or sample per 4- itoring scheme will help the grid operators to take preventive or 10 seconds whereas new sensors like Phasor Measurement Units corrective measures ahead of time to mitigate any disturbance be- (PMUs) could provide upto 120 measurements or samples per sec- fore they develop into wide-spread. A protptype of the scheme is ond. Moreover, PMUs provide more precise measurements with demonstrated on a benchmark 3 machines 9 bus system and the time stamp having microsecond accuracy [2]. -
Preprocessing C++ : Meta-Class Aspects
Preprocessing C++ : Meta-Class Aspects Edward D. Willink Racal Research Limited, Worton Drive, Reading, England +44 118 923 8278 [email protected] Vyacheslav B. Muchnick Department of Computing, University of Surrey, Guildford, England +44 1483 300800 x2206 [email protected] ABSTRACT C++ satisfies the previously conflicting goals of Object-Orientation and run-time efficiency within an industrial strength language. Run-time efficiency is achieved by ignoring the meta-level aspects of Object-Orientation. In a companion paper [15] we show how extensions that replace the traditional preprocessor lexical substitution by an Object-Oriented meta-level substitution fit naturally into C++. In this paper, we place those extensions in the context of a compile-time meta-level, in which application meta-programs can execute to browse, check or create program declarations. An extended example identifies the marshalling aspect as a programming concern that can be fully separated and automatically generated by an application meta-program. Keywords Object-Oriented Language; Preprocessor; C++; Meta-Level; Composition; Weaving; Aspect-Oriented Programming; Pattern Implementation 1 INTRODUCTION Prior to C++, Object Orientation, as exemplified by Smalltalk, was perceived to be inherently inefficient because of the run-time costs associated with message dispatch. C++ introduced a more restrictive Object Model that enabled most of the run-time costs to be resolved by compile-time computation. As a result Object Orientation in C++ is efficient and widely used. C++ requires that the layout of objects be frozen at compile-time, and that the type of the recipient of any message is known. The layout constraint enables a single contiguous memory allocation for each object. -
Shells and Shell Programming
Shells & Shell Programming (Part A) Software Tools EECS2031 Winter 2018 Manos Papagelis Thanks to Karen Reid and Alan J Rosenthal for material in these slides SHELLS 2 What is a Shell • A shell is a command line interpreter that is the interface between the user and the OS. • The shell: – analyzes each command – determines what actions are to be performed – performs the actions • Example: wc –l file1 > file2 3 Which shell? • sh – Bourne shell – Most common, other shells are a superset – Good for programming • csh or tcsh – command-line default on EECS labs – C-like syntax – Best for interactive use. • bash – default on Linux (Bourne again shell) – Based on sh, with some csh features. • korn – written by David Korn – Based on sh – Some claim best for programming. – Commercial product. 4 bash versus sh • On EECS labs, when you run sh, you are actually running bash. • bash is a superset of sh. • For EECS2031, you will be learning only the features of the language that belong to sh. 5 Changing your shell • I recommend changing your working shell on EECS to bash – It will make it easier to test your shell programs. – You will only need to learn one set of syntax. • What to do: – echo $SHELL (to check your current shell) – chsh <userid> bash – Logout and log back in. – .profile is executed every time you log in, so put your environment variables there 6 Standard Streams • Preconnected input and output channels between a computer program and its environment. There are 3 I/O connections: – standard input (stdin) – standard output (stdout) – standard