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  • Understanding hand written lexers

    - by Cole Johnson
    I am going to make a compiler for C (C99; I own the standards PDF), written in C (go figure) and looking up on how compilers work on Wikipedia has told me a lot. However, after reading up on lexers has confused me. The Wikipedia page states that: the GNU Compiler Collection (gcc) uses hand-written lexers I have tried googling what a hand written lexer and have come up with nothing except for "making a flowchart that describes how it should function", however, isn't that how all software development should be done? So my question is: "What is a hand written lexer?"

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  • Does a prose to code compiler exist?

    - by Raynos
    I have seen some horrible code in my time including people virtually duplicating the code in comments // add 4 to x x+=4; // for each i in 0 to 9 for (int i = 0; i < 10; i++) { // multiply x by i x *= i; } Taking this concept further, I'm curious whether prose to code compilers exist. Is there a valid use case for English prose to code? Do compilers exist that do this? The distinction between this and auto generated code, is that auto generated code is generally always a subset of a project. Can we have complete projects auto generated from english prose? I realise that this might overlap with the concept of declarative languages.

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  • C++ compiler structures such as Virtual method Table etc

    - by Roger
    I am aware of the C++ Virtual Table which allows dynamic dispatch for doing things at runtime (although if I am honest I am not completely sure of the full list of things it achieves). I am wondering what other "low level" aspects of C++ are there, which one doesnt usually come across when learning the C++ language? Things like: -How is multithreading and locking on objects performed? -Overloading/overwriting functions -Generics Are there other "structures", similar to the vtable, which assist with these types of things on a lower level? (and if anyone can help with what the VTable actually does it would be most appreciated!)

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  • How do I find the dependencies for a program before trying to compile it?

    - by Ubuntu_beginner
    I was trying to cross-compile a program for ARM. While compiling I was very much irritated as I had to look for a number of dependencies e.g fatal error: abc/xyz.h: No such file or directory compilation terminated. After ensuring that compiler gets the missing files, when I recompiled, I got same error for about 30 files. I have no idea if that is normal behaviour. If it is normal, is there a method which can help the compiler find the dependencies on its own? If that is not normal, then please explain what I'm doing wrong.

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  • Visual Studio 2012 not building dependent projects

    - by user1438940
    I just upgraded a VS2010 project to VS2012 and am now having a problem where dependent projects are not building on demand. For instance, say I have the following projects in my solution: Library A ConsoleApp 1 Where ConsoleApp 1 references Library A. If I change the signature of a method in a class in Library A and run ConsoleApp 1, there will be a compiler error due to ConsoleApp 1 not seeing my changes because running ConsoleApp 1 did NOT cause Library A to build. If I manually build Library A, then manually build ConsoleApp 1, it works fine. However, I would expect that running ConsoleApp 1 should cause any dependent projects to be rebuilt before launching. Could I have something configured incorrectly? Or is this a bug in VS2012?

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  • Can you use the Phoenix compiler as a more powerful NGEN?

    - by TraumaPony
    In case you don't know of Phoenix, it's a compiler framework from Microsoft that's apparantly going to be the foundation of all their new compilers. It can read in code from CIL, x86, x64, and IA64; and emit code in x86, x64, IA64, or CIL. Can I use it to transform a pure .Net app into a pure native app? By which I mean, it will not have to load any .Net .dll (not even mscoree), and will have the same semantics? This is excluding Reflection, of course.

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  • How to make php-closure compiler output to a predefined file name? (Updated)

    - by Mohammad
    Php-closure compiler (linked to source code) currently writes the compiled code to a md5 encoded filename. How can I make it so it write the compiled code to a predefined name like compiled_code.js? . . I think it has to do with the write() function on Line 164. It gets the filename via the _getCacheFileName() function (Line 272). function _getCacheFileName() { return $this->_cache_dir . $this->_getHash() . ".js"; } I've tried altering it to this: function _getCacheFileName() { //return $this->_cache_dir . $this->_getHash() . ".js"; return 'copiled_code.js'; } without any results. Thanks to all of you in advance!

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  • How to generate a compiler error based on an attribute being missing in C#?

    - by RodH257
    I create a number of add-ins for the Revit Structure API. Each tool has to habe a class which implements the interface IExternalCommand. In the latest version of Revit, for your tool to work you need to have two attributes on the class that implements that interface: [Regeneration(RegenerationOption.Manual)] [Transaction(TransactionMode.Automatic)] The values in brackets can change, but there must be something there. Often I am finding myself forgetting to put the attributes on, then when it comes to runtime it crashes. Is there any way in Visual Studio 2010 to add a compiler warning or error saying that if your class implements that interface it must have those 2 attributes? I have resharper if that helps. Can anyone point me into the right direction?

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  • Java generics: What is the compiler's issue here? ("no unique maximal instance")

    - by Epaga
    I have the following methods: public <T> T fromJson( Reader jsonData, Class<T> clazz ) { return fromJson( jsonData, (Type)clazz ); } public <T> T fromJson( Reader jsonData, Type clazz ) { ... } The compiler is saying about the first method: type parameters of <T>T cannot be determined; no unique maximal instance exists for type variable T with upper bounds T,java.lang.Object return fromJson( jsonData, (Type)clazz ); ^ What is the problem?

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  • How do you control what your C compiler Optimizes?

    - by Jordan S
    I am writing the firmware for an embedded device in C using the Silicon Labs IDE and the SDCC compiler. The device architecture is based on the 8051 family. The function in question is shown below. The function is used to set the ports on my MCU to drive a stepper motor. It gets called in by an interrupt handler. The big switch statement just sets the ports to the proper value for the next motor step. The bottom part of the function looks at an input from a hall effect sensor and a number of steps moved in order to detect if the motor has stalled. The problem is, for some reason the second IF statement that looks like this if (StallDetector > (GapSize + 20)) { HandleStallEvent(); } always seems to get optimized out. If I try to put a breakpoint at the HandleStallEvent() call the IDE gives me a message saying "No Address Correlation to this line number". I am not really good enough at reading assembly to tell what it is doing but I have pasted a snippet from the asm output below. Any help would be much appreciated. void OperateStepper(void) { //static bit LastHomeMagState = HomeSensor; static bit LastPosMagState = PosSensor; if(PulseMotor) { if(MoveDirection == 1) // Go clockwise { switch(STEPPER_POSITION) { case 'A': STEPPER_POSITION = 'B'; P1 = 0xFD; break; case 'B': STEPPER_POSITION = 'C'; P1 = 0xFF; break; case 'C': STEPPER_POSITION = 'D'; P1 = 0xFE; break; case 'D': STEPPER_POSITION = 'A'; P1 = 0xFC; break; default: STEPPER_POSITION = 'A'; P1 = 0xFC; } //end switch } else // Go CounterClockwise { switch(STEPPER_POSITION) { case 'A': STEPPER_POSITION = 'D'; P1 = 0xFE; break; case 'B': STEPPER_POSITION = 'A'; P1 = 0xFC; break; case 'C': STEPPER_POSITION = 'B'; P1 = 0xFD; break; case 'D': STEPPER_POSITION = 'C'; P1 = 0xFF; break; default: STEPPER_POSITION = 'A'; P1 = 0xFE; } //end switch } //end else MotorSteps++; StallDetector++; if(PosSensor != LastPosMagState) { StallDetector = 0; LastPosMagState = PosSensor; } else { if (PosSensor == ON) { if (StallDetector > (MagnetSize + 20)) { HandleStallEvent(); } } else if (PosSensor == OFF) { if (StallDetector > (GapSize + 20)) { HandleStallEvent(); } } } } //end if PulseMotor } ... and the asm output for the the bottom part of this function... ; C:\SiLabs\Optec Programs\HSFW_HID_SDCC_2\MotionControl.c:653: if(PosSensor != LastPosMagState) mov c,_P1_4 jb _OperateStepper_LastPosMagState_1_1,00158$ cpl c 00158$: jc 00126$ C$MotionControl.c$655$3$7 ==. ; C:\SiLabs\Optec Programs\HSFW_HID_SDCC_2\MotionControl.c:655: StallDetector = 0; clr a mov _StallDetector,a mov (_StallDetector + 1),a C$MotionControl.c$657$3$7 ==. ; C:\SiLabs\Optec Programs\HSFW_HID_SDCC_2\MotionControl.c:657: LastPosMagState = PosSensor; mov c,_P1_4 mov _OperateStepper_LastPosMagState_1_1,c ret 00126$: C$MotionControl.c$661$2$8 ==. ; C:\SiLabs\Optec Programs\HSFW_HID_SDCC_2\MotionControl.c:661: if (PosSensor == ON) jb _P1_4,00123$ C$MotionControl.c$663$4$9 ==. ; C:\SiLabs\Optec Programs\HSFW_HID_SDCC_2\MotionControl.c:663: if (StallDetector > (MagnetSize + 20)) mov a,_MagnetSize mov r2,a rlc a subb a,acc mov r3,a mov a,#0x14 add a,r2 mov r2,a clr a addc a,r3 mov r3,a clr c mov a,r2 subb a,_StallDetector mov a,r3 subb a,(_StallDetector + 1) jnc 00130$ C$MotionControl.c$665$5$10 ==. ; C:\SiLabs\Optec Programs\HSFW_HID_SDCC_2\MotionControl.c:665: HandleStallEvent(); ljmp _HandleStallEvent 00123$: C$MotionControl.c$668$2$8 ==. ; C:\SiLabs\Optec Programs\HSFW_HID_SDCC_2\MotionControl.c:668: else if (PosSensor == OFF) jnb _P1_4,00130$ C$MotionControl.c$670$4$11 ==. ; C:\SiLabs\Optec Programs\HSFW_HID_SDCC_2\MotionControl.c:670: if (StallDetector > (GapSize + 20)) mov a,#0x14 add a,_GapSize mov r2,a clr a addc a,(_GapSize + 1) mov r3,a clr c mov a,r2 subb a,_StallDetector mov a,r3 subb a,(_StallDetector + 1) jnc 00130$ C$MotionControl.c$672$5$12 ==. ; C:\SiLabs\Optec Programs\HSFW_HID_SDCC_2\MotionControl.c:672: HandleStallEvent(); C$MotionControl.c$678$2$1 ==. XG$OperateStepper$0$0 ==. ljmp _HandleStallEvent 00130$: ret It looks to me like the compiler is NOT optimizing out this second if statement from the looks of the asm but if that is the case why does the IDE not allow me so set a breakpoint there? Maybe it's just a dumb IDE!

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  • Should you correct compiler warnings about type conversions using explicit typecasts?

    - by BastiBechtold
    In my current project, the compiler shows hundreds of warnings about type conversions. There is a lot of code like this iVar = fVar1*fVar2/fVar3; // or even iVar = fVar1*fVar2/fVar3+.5f; which intentionally assign float values to int. Of course, I could fix these warnings using iVar = int(...); but that looks kind of ugly. Would you rather live with the ugliness or live with the warnings? Or is there even a clean solution?

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  • Where does the compiler store methods for C++ classes?

    - by Mashmagar
    This is more a curiosity than anything else... Suppose I have a C++ class Kitty as follows: class Kitty { void Meow() { //Do stuff } } Does the compiler place the code for Meow() in every instance of Kitty? Obviously repeating the same code everywhere requires more memory. But on the other hand, branching to a relative location in nearby memory requires fewer assembly instructions than branching to an absolute location in memory on modern processors, so this is potentially faster. I suppose this is an implementation detail, so different compilers may perform differently. Keep in mind, I'm not considering static or virtual methods here.

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  • Explicitly typing variables causes compiler to think an instance of a builtin type doesn't have a pr

    - by wallacoloo
    I narrowed the causes of an AS3 compiler error 1119 down to code that looks similar to this: var test_inst:Number = 2.953; trace(test_inst); trace(test_inst.constructor); I get the error "1119: Access of possibly undefined property constructor through a reference with static type Number." Now if I omit the variable's type, I don't get that error: var test_inst = 2.953; trace(test_inst); trace(test_inst.constructor); it produces the expected output: 2.953 [class Number] So what's the deal? I like explicitly typing variables, so is there any way to solve this error other than not providing the variable's type?

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  • Is C# compiler not reporting all errors at once at each compile?

    - by Joan Venge
    When I am compiling this project, it show like 400+ errors in the Error List window, then I go to error sites, fix some, and the number goes to say 120+ errors, and then after fixing some more, the next compile reports like 400+ again. I can see that different files are coming in in the Error List window, so I am thinking the compiler aborts after a certain number of errors? If so, what's the reason for this? Is it not supposed to gather all the errors that are present in the project even if they are over 10K+?

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  • org.apache.jasper.JasperException .... Unterminated &lt;%@ page tag

    - by Ankur
    I get org.apache.jasper.JasperException: /index.jsp(2,1) Unterminated <%@ page tag The page tags look like this: <%@ page import="java.util.*" %> <%@ page import="au.edu.uwa.peb.autoextractor.model.ScanResultItem"; %> This seems to indicate to me that a < does not have a corresponding tag ... is this so ... my IDE does not highlight any errors so how can I find this unterminated tag. Is there a JSP validation tool that I can use, perhaps online? The stack trace looks like this: org.apache.jasper.compiler.DefaultErrorHandler.jspError(DefaultErrorHandler.java:40) org.apache.jasper.compiler.ErrorDispatcher.dispatch(ErrorDispatcher.java:407) org.apache.jasper.compiler.ErrorDispatcher.jspError(ErrorDispatcher.java:132) org.apache.jasper.compiler.Parser.parseDirective(Parser.java:520) org.apache.jasper.compiler.Parser.parseTagFileDirectives(Parser.java:1784) org.apache.jasper.compiler.Parser.parse(Parser.java:127) org.apache.jasper.compiler.ParserController.doParse(ParserController.java:255) org.apache.jasper.compiler.ParserController.parseDirectives(ParserController.java:120) org.apache.jasper.compiler.Compiler.generateJava(Compiler.java:165) org.apache.jasper.compiler.Compiler.compile(Compiler.java:332) org.apache.jasper.compiler.Compiler.compile(Compiler.java:312) org.apache.jasper.compiler.Compiler.compile(Compiler.java:299) org.apache.jasper.JspCompilationContext.compile(JspCompilationContext.java:586) org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:317) org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:342) org.apache.jasper.servlet.JspServlet.service(JspServlet.java:267) javax.servlet.http.HttpServlet.service(HttpServlet.java:717)

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  • Is the C++ compiler optimizer allowed to break my destructor ability to be called multiple times?

    - by sharptooth
    We once had an interview with a very experienced C++ developer who couldn't answer the following question: is it necessary to call the base class destructor from the derived class destructor in C++? Obviously the answer is no, C++ will call the base class destructor automagically anyway. But what if we attempt to do the call? As I see it the result will depend on whether the base class destructor can be called twice without invoking erroneous behavior. For example in this case: class BaseSafe { public: ~BaseSafe() { } private: int data; }; class DerivedSafe { public: ~DerivedSafe() { BaseSafe::~BaseSafe(); } }; everything will be fine - the BaseSafe destructor can be called twice safely and the program will run allright. But in this case: class BaseUnsafe { public: BaseUnsafe() { buffer = new char[100]; } ~BaseUnsafe () { delete[] buffer; } private: char* buffer; }; class DerivedUnsafe { public: ~DerivedUnsafe () { BaseUnsafe::~BaseUnsafe(); } }; the explicic call will run fine, but then the implicit (automagic) call to the destructor will trigger double-delete and undefined behavior. Looks like it is easy to avoid the UB in the second case. Just set buffer to null pointer after delete[]. But will this help? I mean the destructor is expected to only be run once on a fully constructed object, so the optimizer could decide that setting buffer to null pointer makes no sense and eliminate that code exposing the program to double-delete. Is the compiler allowed to do that?

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  • Can a conforming C# compiler optimize away a local (but unused) variable if it is the only strong re

    - by stakx
    The title says it all, but let me explain: void Case_1() { var weakRef = new WeakReference(new object()); GC.Collect(); // <-- doesn't have to be an explicit call; just assume that // garbage collection would occur at this point. if (weakRef.IsAlive) ... } In this code example, I obviously have to plan for the possibility that the new'ed object is reclaimed by the garbage collector; therefore the if statement. (Note that I'm using weakRef for the sole purpose of checking if the new'ed object is still around.) void Case_2() { var unusedLocalVar = new object(); var weakRef = new WeakReference(unusedLocalVar); GC.Collect(); // <-- doesn't have to be an explicit call; just assume that // garbage collection would occur at this point. Debug.Assert(weakReferenceToUseless.IsAlive); } The main change in this code example from the previous one is that the new'ed object is strongly referenced by a local variable (unusedLocalVar). However, this variable is never used again after the weak reference (weakRef) has been created. Question: Is a conforming C# compiler allowed to optimize the first two lines of Case_2 into those of Case_1 if it sees that unusedLocalVar is only used in one place, namely as an argument to the WeakReference constructor? i.e. is there any possibility that the assertion in Case_2 could ever fail?

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  • Java Compiler Creation Help..Please

    - by Brian
    I need some help with my code here...What we are trying to do is make a compiler that will read a file containing Machine Code and converting it to 100 lines of 4 bits example: this code is the machine code being converting to opcode and operands. I need some help please.. thanks 799 798 198 499 1008 1108 899 909 898 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Everything compiles but when I go and run my Test.java I get the following OutPut: Exception in thread "main" java.util.NoSuchElementException: No line found at java.util.Scanner.nextLine(Scanner.java:1516) at Compiler.FirstPass(Compiler.java:22) at Compiler.compile(Compiler.java:11) at Test.main(Test.java:5) Here is my class Compiler: import java.io.*; import java.io.DataOutputStream; import java.util.NoSuchElementException; import java.util.Scanner; class Compiler{ private int lc = 0; private int dc = 99; public void compile(String filename) { SymbolList symbolTable = FirstPass(filename); SecondPass(symbolTable, filename); } public SymbolList FirstPass(String filename) { File file = new File(filename); SymbolList temp = new SymbolList(); int dc = 99; int lc = 0; try{ Scanner scan = new Scanner(file); String line = scan.nextLine(); String[] linearray = line.split(" "); while(line!=null){ if(!linearray[0].equals("REM")){ if(!this.isInstruction(linearray[0])){ linearray[0]=removeColon(linearray[0]); if(this.isInstruction(linearray[1])){ temp.add(new Symbol(linearray[0], lc, null)); lc++; } else { temp.add(new Symbol(linearray[0], dc, Integer.valueOf((linearr\ ay[2])))); dc--; } } else { if(!linearray[0].equals("REM")) lc++; } } try{ line = scan.nextLine(); } catch(NoSuchElementException e){ line=null; break; } linearray = line.split(" "); } } catch (FileNotFoundException e) { // TODO Auto-generated catch block e.printStackTrace(); } return temp; } public String makeFilename(String filename) { return filename + ".ex"; } public String removeColon(String str) { if(str.charAt(str.length()-1) == ':'){ return str.substring(0, str.length()-1); } else { return str; } } public void SecondPass(SymbolList symbolTable, String filename){ try { int dc = 99; //Open file for reading File file = new File(filename); Scanner scan = new Scanner(file); //Make filename of new executable file String newfile = makeFilename(filename); //Open Output Stream for writing new file. FileOutputStream os = new FileOutputStream(filename); DataOutputStream dos = new DataOutputStream(os); //Read First line. Split line by Spaces into linearray. String line = scan.nextLine(); String[] linearray = line.split(" "); while(scan.hasNextLine()){ if(!linearray[0].equals("REM")){ int inst=0, opcode, loc; if(isInstruction(linearray[0])){ opcode = getOpcode(linearray[0]); loc = symbolTable.searchName(linearray[1]).getMemloc(); inst = (opcode*100)+loc; } else if(!isInstruction(linearray[0])){ if(isInstruction(linearray[1])){ opcode = getOpcode(linearray[1]); if(linearray[1].equals("STOP")) inst=0000; else { loc = symbolTable.searchName(linearray[2]).getMemloc(); inst = (opcode*100)+loc; } } if(linearray[1].equals("DC")) dc--; } System.out.println(inst); dos.writeInt(inst); linearray = line.split(" "); } if(scan.hasNextLine()) { line = scan.nextLine(); } } scan.close(); for(int i = lc; i <= dc; i++) { dos.writeInt(0); } for(int i = dc+1; i<100; i++){ dos.writeInt(symbolTable.searchLocation(i).getValue()); if(i!=99) dos.writeInt(0); } dos.close(); os.close(); } catch (Exception e) { // TODO Auto-generated catch block e.printStackTrace(); } } public int getOpcode(String inst){ int toreturn = -1; if(isInstruction(inst)){ if(inst.equals("STOP")) toreturn=0; if(inst.equals("LD")) toreturn=1; if(inst.equals("STO")) toreturn=2; if(inst.equals("ADD")) toreturn=3; if(inst.equals("SUB")) toreturn=4; if(inst.equals("MPY")) toreturn=5; if(inst.equals("DIV")) toreturn=6; if(inst.equals("IN")) toreturn=7; if(inst.equals("OUT")) toreturn=8; if(inst.equals("B")) toreturn=9; if(inst.equals("BGTR")) toreturn=10; if(inst.equals("BZ")) toreturn=11; return toreturn; } else { return -1; } } public boolean isInstruction(String totest){ boolean toreturn = false; String[] labels = {"IN", "LD", "SUB", "BGTR", "BZ", "OUT", "B", "STO", "STOP", "AD\ D", "MTY", "DIV"}; for(int i = 0; i < 12; i++){ if(totest.equals(labels[i])) toreturn = true; } return toreturn; } } And here is my class Computer: import java.io.*; import java.util.NoSuchElementException; import java.util.Scanner; class Computer{ private Cpu cpu; private Input in; private OutPut out; private Memory mem; public Computer() throws IOException { Memory mem = new Memory(100); Input in = new Input(); OutPut out = new OutPut(); Cpu cpu = new Cpu(); System.out.println(in.getInt()); } public void run() throws IOException { cpu.reset(); cpu.setMDR(mem.read(cpu.getMAR())); cpu.fetch2(); while (!cpu.stop()) { cpu.decode(); if (cpu.OutFlag()) OutPut.display(mem.read(cpu.getMAR())); if (cpu.InFlag()) mem.write(cpu.getMDR(),in.getInt()); if (cpu.StoreFlag()) { mem.write(cpu.getMAR(),in.getInt()); cpu.getMDR(); } else { cpu.setMDR(mem.read(cpu.getMAR())); cpu.execute(); cpu.fetch(); cpu.setMDR(mem.read(cpu.getMAR())); cpu.fetch2(); } } } public void load() { mem.loadMemory(); } } Here is my Memory class: import java.io.*; import java.util.NoSuchElementException; import java.util.Scanner; class Memory{ private MemEl[] memArray; private int size; private int[] mem; public Memory(int s) {size = s; memArray = new MemEl[s]; for(int i = 0; i < s; i++) memArray[i] = new MemEl(); } public void write (int loc,int val) {if (loc >=0 && loc < size) memArray[loc].write(val); else System.out.println("Index Not in Domain"); } public int read (int loc) {return memArray[loc].read(); } public void dump() { for(int i = 0; i < size; i++) if(i%1 == 0) System.out.println(memArray[i].read()); else System.out.print(memArray[i].read()); } public void writeTo(int location, int value) { mem[location] = value; } public int readFrom(int location) { return mem[location]; } public int size() { return mem.length; } public void loadMemory() { this.write(0, 799); this.write(1, 798); this.write(2, 198); this.write(3, 499); this.write(4, 1008); this.write(5, 1108); this.write(6, 899); this.write(7, 909); this.write(8, 898); this.write(9, 0000); } public void loadFromFile(String filename){ try { FileReader fr = new FileReader(filename); BufferedReader br = new BufferedReader(fr); String read=null; int towrite=0; int l=0; do{ try{ read=br.readLine(); towrite = Integer.parseInt(read); }catch(Exception e){ } this.write(l, towrite); l++; }while(l<100); }catch (Exception e) { // TODO Auto-generated catch block e.printStackTrace(); } } } Here is my Test class: public class Test{ public static void main(String[] args) throws java.io.IOException { Compiler compiler = new Compiler(); compiler.compile("program.txt"); } }

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  • How can I make the C# compiler infer these type parameters automatically?

    - by John Feminella
    I have some code that looks like the following. First I have some domain classes and some special comparators for them. public class Fruit { public int Calories { get; set; } public string Name { get; set; } } public class FruitEqualityComparer : IEqualityComparer<Fruit> { // ... } public class BasketEqualityComparer : IEqualityComparer<IEnumerable<Fruit>> { // ... } Next, I have a helper class called ConstraintChecker. It has a simple BaseEquals method that makes sure some simple base cases are considered: public static class ConstraintChecker { public static bool BaseEquals(T lhs, T rhs) { bool sameObject = l == r; bool leftNull = l == null; bool rightNull = r == null; return sameObject && !leftNull && !rightNull; } There's also a SemanticEquals method which is just a BaseEquals check and a comparator function that you specify. public static bool SemanticEquals<T>(T lhs, T rhs, Func<T, T, bool> f) { return BaseEquals(lhs, rhs) && f(lhs, rhs); } And finally there's a SemanticSequenceEquals method which accepts two IEnumerable<T> instances to compare, and an IEqualityComparer instance that will get called on each pair of elements in the list via Enumerable.SequenceEquals. public static bool SemanticSequenceEquals<T, U, V>(U lhs, U rhs, V comparator) where U : IEnumerable<T> where V : IEqualityComparer<T> { return SemanticEquals(lhs, rhs, (l, r) => lhs.SequenceEqual(rhs, comparator)); } } // end of ConstraintChecker The point of SemanticSequenceEquals is that you don't have to define two comparators whenever you want to compare both IEnumerable<T> and T instances; now you can just specify an IEqualityComparer<T> and it will also handle lists when you invoke SemanticSequenceEquals. So I could get rid of the BasketEqualityComparer class, which would be nice. But there's a problem. The C# compiler can't figure out the types involved when you invoke SemanticSequenceEquals: return ConstraintChecker.SemanticSequenceEquals(lhs, rhs, new FruitEqualityComparer()); If I specify them explicitly, it works: return ConstraintChecker.SemanticSequenceEquals< Fruit, IEnumerable<Fruit>, IEqualityComparer<Fruit> > (lhs, rhs, new FruitEqualityComparer()); What can I change here so that I don't have to write the type parameters explicitly?

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  • loading js files and other dependent js files asynchronously

    - by taber
    I'm looking for a clean way to asynchronously load the following types of javascript files: a "core" js file (hmm, let's just call it, oh i don't know, "jquery!" haha), x number of js files that are dependent on the "core" js file being loaded, and y number of other unrelated js files. I have a couple ideas of how to go about it, but not sure what the best way is. I'd like to avoid loading scripts in the document body. So for example, I want the following 4 javascript files to load asynchronously, appropriately named: /js/my-contact-page-js-functions.js // unrelated/independent script /js/jquery-1.3.2.min.js // the "core" script /js/jquery.color.min.js // dependent on jquery being loaded http://thirdparty.com/js/third-party-tracking-script.js // another unrelated/independent script But this won't work because it's not guaranteed that jQuery is loaded before the color plugin... (function() { a=[ '/js/my-contact-page-functions.js', '/js/jquery-1.4.2.min.js', '/js/jquery.color.js', 'http://cdn.thirdparty.com/third-party-tracking-script.js', ], d=document, h=d.getElementsByTagName('head')[0], s, i, l=a.length; for(i=0;i<l;i++){ s=d.createElement('script'); s.type='text/javascript'; s.async=true; s.src=a[i]; h.appendChild(s); } })(); Is it pretty much not possible to load jquery and the color plugin asynchronously? (Since the color plugin requires that jQuery is loaded first.) The first method I was considering is to just combine the color plugin script with jQuery source into one file. Then another idea I had was loading the color plugin like so: $(window).ready(function() { $.getScript("/js/jquery.color.js"); }); Anyone have any thoughts on how you'd go about this? Thanks!

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  • C++: Trouble with dependent types in templates

    - by Rosarch
    I'm having trouble with templates and dependent types: namespace Utils { void PrintLine(const string& line, int tabLevel = 0); string getTabs(int tabLevel); template<class result_t, class Predicate> set<result_t> findAll_if(typename set<result_t>::iterator begin, set<result_t>::iterator end, Predicate pred) // warning C4346 { set<result_t> result; return findAll_if_rec(begin, end, pred, result); } } namespace detail { template<class result_t, class Predicate> set<result_t> findAll_if_rec(set<result_t>::iterator begin, set<result_t>::iterator end, Predicate pred, set<result_t> result) { typename set<result_t>::iterator nextResultElem = find_if(begin, end, pred); if (nextResultElem == end) { return result; } result.add(*nextResultElem); return findAll_if_rec(++nextResultElem, end, pred, result); } } Compiler complaints, from the location noted above: warning C4346: 'std::set<result_t>::iterator' : dependent name is not a type. prefix with 'typename' to indicate a type error C2061: syntax error : identifier 'iterator' What am I doing wrong?

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  • What do I need to know to design a language and write a interpreter for it?

    - by alFReD NSH
    I know this question has been asked and even there are thousands of books and articles about it. But the problem is that there are too many, and I don't know are they good enough, I have to design a language and write a interpreter for it. The base language is javascript (using nodejs) but it's ok if the compiler was written in another language that I can use from node. I had done a research about compiler compilers in JS, there is jison (Bison implementaion in JS), waxeye, peg.js. I decided to give jison a try, due to the popularity and its being used by coffee script, so it should be able to cover my language too. The grammar definition syntax is similar to bison. But when I tried read the bison manual it seemed very hard to understand for me. And I think it's because I don't know a lot of things about what I'm doing. Like I don't what is formal language theory. I am experienced in Javascript (I'm more talented in JS than most average programmers). And also know basic C and C++ (not much experience but can write a working code for basic things). I haven't had any formal education, so I may not be familiar with some software engineering and computer science principles. Though everyday I try to grasp a lot of articles and improve. So I'm asking if you know any good book or article that can help me. Please also write why the resource you're suggesting is good. --update-- The language I'm trying to create, is not really complicated. All it has is expressions (with or without units), comparisons and logical operators. There are no functions, loops, ... The goal is to create a language that non-programmers can easily learn. And to write customized validations and calculations.

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  • IP-dependent local port-forwarding on Linux

    - by chronos
    I have configured my server's sshd to listen on a non-standard port 42. However, at work I am behind a firewall/proxy, which only allow outgoing connections to ports 21, 22, 80 and 443. Consequently, I cannot ssh to my server from work, which is bad. I do not want to return sshd to port 22. The idea is this: on my server, locally forward port 22 to port 42 if source IP is matching the external IP of my work's network. For clarity, let us assume that my server's IP is 169.1.1.1 (on eth1), and my work external IP is 169.250.250.250. For all IPs different from 169.250.250.250, my server should respond with an expected 'connection refused', as it does for a non-listening port. I'm very new to iptables. I have briefly looked through the long iptables manual and these related / relevant questions: http://serverfault.com/questions/57872/iptables-question-forwarding-port-x-to-an-ssh-port-of-different-machine-on-the-n http://serverfault.com/questions/140622/how-can-i-port-forward-with-iptables However, those questions deal with more complicated several-host scenarios, and it is not clear to me which tables and chains I should use for local port-forwarding, and if I should have 2 rules (for "question" and "answer" packets), or only 1 rule for "question" packets. So far I have only enabled forwarding via sysctl. I will start testing solutions tomorrow, and will appreciate pointers or maybe case-specific examples for implementing my simple scenario. Is the draft solution below correct? iptables -A INPUT [-m state] [-i eth1] --source 169.250.250.250 -p tcp --destination 169.1.1.1:42 --dport 22 --state NEW,ESTABLISHED,RELATED -j ACCEPT Should I use the mangle table instead of filter? And/or FORWARD chain instead of INPUT?

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