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• Please suggest what is wrong with this string reversal function?

  - by AKS

  This code is compiling clean. But when I run this, it gives exception "Access violation writing location" at line 9. void reverse(char *word) { int len = strlen(word); len = len-1; char * temp= word; int i =0; while (len >=0) { word[i] = temp[len-1]; //line9 ++i;--len; } word[i] = '\0'; }

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• Unintentional concatenation in Bison/Yacc grammar.

  - by troutwine

  I am experimenting with lex and yacc and have run into a strange issue, but I think it would be best to show you my code before detailing the issue. This is my lexer: %{ #include <stdlib.h> #include <string.h> #include "y.tab.h" void yyerror(char *); %} %% [a-zA-Z]+ { yylval.strV = yytext; return ID; } [0-9]+ { yylval.intV = atoi(yytext); return INTEGER; } [\n] { return *yytext; } [ \t] ; . yyerror("invalid character"); %% int yywrap(void) { return 1; } This is my parser: %{ #include <stdio.h> int yydebug=1; void prompt(); void yyerror(char *); int yylex(void); %} %union { int intV; char *strV; } %token INTEGER ID %% program: program statement EOF { prompt(); } | program EOF { prompt(); } | { prompt(); } ; args: /* empty */ | args ID { printf(":%s ", $<strV>2); } ; statement: ID args { printf("%s", $<strV>1); } | INTEGER { printf("%d", $<intV>1); } ; EOF: '\n' %% void yyerror(char *s) { fprintf(stderr, "%s\n", s); } void prompt() { printf("> "); } int main(void) { yyparse(); return 0; } A very simple language, consisting of no more than strings and integer and a basic REPL. Now, you'll note in the parser that args are output with a leading colon, the intention being that, when combined with the first pattern of the rule of the statement the interaction with the REPL would look something like this: > aaa aa a :aa :a aaa> However, the interaction is this: > aaa aa a :aa :a aaa aa aa > Why does the token ID in the following rule statement: ID args { printf("%s", $<strV>1); } | INTEGER { printf("%d", $<intV>1); } ; have the semantic value of the total input string, newline included? How can my grammar be reworked so that the interaction I intended?

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• Container item implementation

  - by onurozcelik

  Hi, I am working in Train Traffic Controller software project. My responsibility in this project is to develop the visual railroad GUI. We are implementing the project with Qt. By now I am using QGraphicsLinearLayout to hold my items. I am using the layout because I do not want to calculate coordinates of each item. So far I wrote item classes to add the layout. For instance SwitchItem class symbolizes railroad switch in real world. Each item class is responsible for its own painting and events. So far so good. Now I need a composite item that can contain two or more item. This class is going to be responsible for painting the items contained in it. I need this class because I have to put two or more items inside same layout cell. If I don' t put them in same cell I can' t use layout. See the image below. BlockSegmentItem and SignalItem inside same cell. Here is my compositeitem implementation. #include "compositeitem.h" CompositeItem::CompositeItem(QString id,QList<FieldItem *> _children) { children = _children; } CompositeItem::~CompositeItem() { } QRectF CompositeItem::boundingRect() const { FieldItem *child; QRectF rect(0,0,0,0); foreach(child,children) { rect = rect.united(child->boundingRect()); } return rect; } void CompositeItem::paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget ) { FieldItem *child; foreach(child,children) { child->paint(painter,option,widget); } } QSizeF CompositeItem::sizeHint(Qt::SizeHint which, const QSizeF &constraint) const { QSizeF itsSize(0,0); FieldItem *child; foreach(child,children) { // if its size empty set first child size to itsSize if(itsSize.isEmpty()) itsSize = child->sizeHint(Qt::PreferredSize); else { QSizeF childSize = child->sizeHint(Qt::PreferredSize); if(itsSize.width() < childSize.width()) itsSize.setWidth(childSize.width()); itsSize.setHeight(itsSize.height() + childSize.height()); } } return itsSize; } void CompositeItem::contextMenuEvent(QGraphicsSceneContextMenuEvent *event) { qDebug()<<"Test"; } This code works good with painting but when it comes to item events it is problematic. QGraphicsScene treats the composite item like a single item which is right for layout but not for events. Because each item has its own event implementation.(e.g. SignalItem has its special context menu event.) I have to handle item events seperately. Also I need a composite item implementation for the layout. How can I overcome this dilemma?

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• What am I not getting about this abstract class implementation?

  - by Schnapple

  PREFACE: I'm relatively inexperienced in C++ so this very well could be a Day 1 n00b question. I'm working on something whose long term goal is to be portable across multiple operating systems. I have the following files: Utilities.h #include <string> class Utilities { public: Utilities() { }; virtual ~Utilities() { }; virtual std::string ParseString(std::string const& RawString) = 0; }; UtilitiesWin.h (for the Windows class/implementation) #include <string> #include "Utilities.h" class UtilitiesWin : public Utilities { public: UtilitiesWin() { }; virtual ~UtilitiesWin() { }; virtual std::string ParseString(std::string const& RawString); }; UtilitiesWin.cpp #include <string> #include "UtilitiesWin.h" std::string UtilitiesWin::ParseString(std::string const& RawString) { // Magic happens here! // I'll put in a line of code to make it seem valid return ""; } So then elsewhere in my code I have this #include <string> #include "Utilities.h" void SomeProgram::SomeMethod() { Utilities *u = new Utilities(); StringData = u->ParseString(StringData); // StringData defined elsewhere } The compiler (Visual Studio 2008) is dying on the instance declaration c:\somepath\somecode.cpp(3) : error C2259: 'Utilities' : cannot instantiate abstract class due to following members: 'std::string Utilities::ParseString(const std::string &)' : is abstract c:\somepath\utilities.h(9) : see declaration of 'Utilities::ParseString' So in this case what I'm wanting to do is use the abstract class (Utilities) like an interface and have it know to go to the implemented version (UtilitiesWin). Obviously I'm doing something wrong but I'm not sure what. It occurs to me as I'm writing this that there's probably a crucial connection between the UtilitiesWin implementation of the Utilities abstract class that I've missed, but I'm not sure where. I mean, the following works #include <string> #include "UtilitiesWin.h" void SomeProgram::SomeMethod() { Utilities *u = new UtilitiesWin(); StringData = u->ParseString(StringData); // StringData defined elsewhere } but it means I'd have to conditionally go through the different versions later (i.e., UtilitiesMac(), UtilitiesLinux(), etc.) What have I missed here?

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• How do I get the next token in a Cstring if I want to use it as an int? (c++)

  - by Van

  My objective is to take directions from a user and eventually a text file to move a robot. The catch is that I must use Cstrings(such as char word[];) rather than the std::string and tokenize them for use. the code looks like this: void Navigator::manualDrive() { char uinput[1]; char delim[] = " "; char *token; cout << "Enter your directions below: \n"; cin.ignore(); cin.getline (uinput, 256); token=strtok(uinput, delim); if(token == "forward") { int inches; inches=token+1; travel(inches); } } I've never used Cstrings I've never tokenized anything before, and I don't know how to write this. Our T.A.'s expect us to google and find all the answers because they are aware we've never been taught these methods. Everyone in my lab is having much more trouble than usual. I don't know the code to write but I know what I want my program to do. I want it to execute like this: 1) Ask for directions. 2) cin.getline the users input 3) tokenize the inputed string 4) if the first word token == "forward" move to the next token and find out how many inches to move forward then move forward 5) else if the first token == "turn" move to the next token. if the next token == "left" move to the next token and find out how many degrees to turn left I will have to do this for forward x, backward x, turn left x, turn right x, and stop(where x is in inches or degrees). I already wrote functions that tell the robot how to move forward an inch and turn in degrees. I just need to know how to convert the inputted strings to all lowercase letters and move from token to token and convert or extract the numbers from the string to use them as integers. If all is not clear you can read my lab write up at this link: http://www.cs.utk.edu/~cs102/robot_labs/Lab9.html If anything is unclear please let me know, and I will clarify as best I can.

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• How to create constant NSString by concatenating strings in Obj-C ?

  - by eric-morand

  Hi guys, I'm trying to instanciate a constant NSString by concatanating other NSString instances. Here is what I'm doing in my implementation file : static NSString *const MY_CONST = @"TEST"; static NSString *const MY_CONCATENATE_CONST = [NSString stringWithFormat:@"STRING %@", MY_CONST]; It leads to the following compilation error : Initializer element is not constant I suppose this is because stringWithFormat doesn't return a constant NSString, but since there is no other way to concatenate strings in Obj-C, what am I supposed to do ? Thanks for your help, Eric.

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• How to get values after dictionary sorting by values with linq

  - by user301639

  hey, I've a dictionary, which i sorted by value with linq, how can i get those sorted value from the sorted result i get that's what i did so far Dictionary<char, int> lettersAcurr = new Dictionary<char, int>();//sort by int value var sortedDict = (from entry in lettersAcurr orderby entry.Value descending select entry); during the debug i can see that sortedDic has a KeyValuePar, but i cant accesses to it thanks for help

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• strtok problem in calling

  - by Moony

  I have a function using strtok like this void f1(char *name) { ... char *tmp; tmp = strtok(names, " ,"); while(tmp) { ... tmp = strtok(NULL, " ,"); } ... } And i have a call f1("abc,def"); Problem is that in first call f1 gets abc,def and in 2nd call gets just abc I am confused.. Why is this so?

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• string compare function in c programming language that has 3 outputs

  - by Roshan

  Write your own version of the strcmp function string_compare. Supply a main program that will test each of the 3 differing outcomes. int string_compare(char *s, char *t); returns <0 if s is lexically before t 0 if s is identical to t >0 if s is lexically after t

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• Mocking a concrete class : templates and avoiding conditional compilation

  - by AshirusNW

  I'm trying to testing a concrete object with this sort of structure. class Database { public: Database(Server server) : server_(server) {} int Query(const char* expression) { server_.Connect(); return server_.ExecuteQuery(); } private: Server server_; }; i.e. it has no virtual functions, let alone a well-defined interface. I want to a fake database which calls mock services for testing. Even worse, I want the same code to be either built against the real version or the fake so that the same testing code can both: Test the real Database implementation - for integration tests Test the fake implementation, which calls mock services To solve this, I'm using a templated fake, like this: #ifndef INTEGRATION_TESTS class FakeDatabase { public: FakeDatabase() : realDb_(mockServer_) {} int Query(const char* expression) { MOCK_EXPECT_CALL(mockServer_, Query, 3); return realDb_.Query(); } private: // in non-INTEGRATION_TESTS builds, Server is a mock Server with // extra testing methods that allows mocking Server mockServer_; Database realDb_; }; #endif template <class T> class TestDatabaseContainer { public: int Query(const char* expression) { int result = database_.Query(expression); std::cout << "LOG: " << result << endl; return result; } private: T database_; }; Edit: Note the fake Database must call the real Database (but with a mock Server). Now to switch between them I'm planning the following test framework: class DatabaseTests { public: #ifdef INTEGRATION_TESTS typedef TestDatabaseContainer<Database> TestDatabase ; #else typedef TestDatabaseContainer<FakeDatabase> TestDatabase ; #endif TestDatabase& GetDb() { return _testDatabase; } private: TestDatabase _testDatabase; }; class QueryTestCase : public DatabaseTests { public: void TestStep1() { ASSERT(GetDb().Query(static_cast<const char *>("")) == 3); return; } }; I'm not a big fan of that compile-time switching between the real and the fake. So, my question is: Whether there's a better way of switching between Database and FakeDatabase? For instance, is it possible to do it at runtime in a clean fashion? I like to avoid #ifdefs. Also, if anyone has a better way of making a fake class that mimics a concrete class, I'd appreciate it. I don't want to have templated code all over the actual test code (QueryTestCase class). Feel free to critique the code style itself, too. You can see a compiled version of this code on codepad.

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• Reading a file with a supplied name in C++

  - by Cosmina

  I must read a file with a given name (it's caled "hamlet.txt"). The class used to read the file is defined like this #ifndef READWORDS_H #define READWORDS_H /** * ReadWords class. Provides mechanisms to read a text file, and return * capitalized words from that file. */ using namespace std; #include <string> #include <fstream> class ReadWords { public: /** * Constructor. Opens the file with the default name "text.txt". * Program exits with an error message if the file does not exist. */ ReadWords(); /** * Constructor. Opens the file with the given filename. * Program exits with an error message if the file does not exist. * @param filename - a C string naming the file to read. */ ReadWords(char *filename); My definition of the members of the classis this: #include<string> #include<fstream> #include<iostream> #include "ReadWords.h" using namespace std; ReadWords::ReadWords() { wordfile.open("text.txt"); if( !wordfile ) { cout<<"Errors while opening the file!"<<endl; } } ReadWords::ReadWords(char *filename) { wordfile.open(filename); if ( !wordfile ) { cout<<"Errors while opening the file!"<<endl; } wordfile>>nextword; } And the main to test it. using namespace std; #include #include #include "ReadWords.h" int main() { char name[30]; cout<<"Please input a name for the file that you wish to open"; cin>>name; ReadWords x( name[] ); } When I complie it gives me the error: main.cpp:14: error: expected primary-expression before ']' token I know it's got something to do with the function ReadWords( char *filename), but I do not know what. Any help please?

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• warning: returning reference to temporary

  - by Jack

  I have a function like this const string &SomeClass::Foo(int Value) { if (Value < 0 or Value > 10) return ""; else return SomeClass::StaticMember[i]; } I get warning: returning reference to temporary. Why is that? I thought the both values the function returns (reference to const char* "" and reference to a static member) cannot be temporary.

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• Java Operator Precedence Comparison

  - by Andrew

  Does java have a built-in method to compare precedence of two operators? For example, if I have a char '/' and a char '+' is there a method I can call that compares the two and returns true/false if the first is greater than the second (e.g. true)?

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• string parsing occurrence in c

  - by Dan74

  I have a string as const char *str = "Hello, this is an example of my string"; How could I get everything after the first comma. So for this instance: this is an example of my string I was planing to do something like: // pseudocode char *a, *b; loop { if((a = strchr(l, ',')) == NULL) break; b++; // but not sure here } printf("%s",a); Thanks

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• What is your best example of a violation of the Single Responsibility Principle?

  - by Jon Kruger

  I'm looking for some good examples of code that violates the Single Responsibility Principle. Don't show me any examples from Uncle Bob's books or web sites since those are plastered all over the internet, like this one: interface Modem { public void dial(String pno); public void hangup(); public void send(char c); public char recv(); }

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• Explain why MickroC pic18f4550 HID example works

  - by Dr Deo

  MickroC compiler has a library for HID(Human Interface Device) usb communication. In the supplied samples, they specify that the buffers below should be in USB ram and use a pic18f4550. unsigned char readbuff[64] absolute 0x500; // Buffers should be in USB RAM, please consult datasheet unsigned char writebuff[64] absolute 0x540; But the pic18f4550 datasheet says USB ram ranges from 400h to 4FFh So why does their example work when their buffers appear not to be between 400h to 4FFh? Link to full source

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• Need unicode characters in UITableView from SQLlite database

  - by Lee Armstrong

  I have some NSString varibales that incude items like Ð and Õ and if I do cell.textLabel.text = person.name; and if it contains one of those characters the cell.textlabel is blank! I have discovered that if I use NSString *col1 = [NSString stringWithUTF8String:(char *)sqlite3_column_text(compiledStatement, 0)]; To pull my data back it pulls back null, however using the deprectared method NSString *col1 = [NSString stringWithCString:(char *)sqlite3_column_text(compiledStatement, 0)]; Shows the characters! Any ideas?

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• C array initialization.

  - by chrisdew

  Why does static char *opcode_str[] = { "DATA" , "DATA_REQUEST_ACK" , "ACK_TIMER_EXPIRED" , "ACK_UNEXPECTED_SEQ" , "ACK_AS_REQUESTED" } ; work, but static char **opcode_str = { "DATA" , "DATA_REQUEST_ACK" , "ACK_TIMER_EXPIRED" , "ACK_UNEXPECTED_SEQ" , "ACK_AS_REQUESTED" } ; fails with SEGV when opcode_str[0] is printf'd? I think it's because the second listing has not allocated memory for the five element array of pointers, but I need a more comprehensive explanation. All the best, Chris.

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• Why Constant Keyword is not introduced In Java?

  - by harigm

  I am curious learner of Java, I was thinking on one topic "CONSTANTS" I have learnt that Java allows us to declare constants by using "Final" keyword. My question is Java didnot introduce Constant(Const) Keyword. Since many people say it has come from C++, in C++ we have Const keyword Is there any strong reason behind, Please share your thoughts on this.

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• Which is preferred: foo(void) or foo() in C++

  - by George2

  I have seen two styles of defining conversion operator overload in C++, operator int* (void) const operator int*() const Question 1. I think the two styles (whether add void or not) have the same function, correct? Question 2. Any preference which is better?

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• Reading and writing C++ vector to a file

  - by JB

  For some graphics work I need to read in a large amount of data as quickly as possible and would ideally like to directly read and write the data structures to disk. Basically I have a load of 3d models in various file formats which take too long to load so I want to write them out in their "prepared" format as a cache that will load much faster on subsequent runs of the program. Is it safe to do it like this? My worries are around directly reading into the data of the vector? I've removed error checking, hard coded 4 as the size of the int and so on so that i can give a short working example, I know it's bad code, my question really is if it is safe in c++ to read a whole array of structures directly into a vector like this? I believe it to be so, but c++ has so many traps and undefined behavour when you start going low level and dealing directly with raw memory like this. I realise that number formats and sizes may change across platforms and compilers but this will only even be read and written by the same compiler program to cache data that may be needed on a later run of the same program. #include <fstream> #include <vector> using namespace std; struct Vertex { float x, y, z; }; typedef vector<Vertex> VertexList; int main() { // Create a list for testing VertexList list; Vertex v1 = {1.0f, 2.0f, 3.0f}; list.push_back(v1); Vertex v2 = {2.0f, 100.0f, 3.0f}; list.push_back(v2); Vertex v3 = {3.0f, 200.0f, 3.0f}; list.push_back(v3); Vertex v4 = {4.0f, 300.0f, 3.0f}; list.push_back(v4); // Write out a list to a disk file ofstream os ("data.dat", ios::binary); int size1 = list.size(); os.write((const char*)&size1, 4); os.write((const char*)&list[0], size1 * sizeof(Vertex)); os.close(); // Read it back in VertexList list2; ifstream is("data.dat", ios::binary); int size2; is.read((char*)&size2, 4); list2.resize(size2); // Is it safe to read a whole array of structures directly into the vector? is.read((char*)&list2[0], size2 * sizeof(Vertex)); }

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• pthread and recursively calling execvp in C

  - by eduke

  To begin I'm sorry for my english :) I looking for a way to create a thread each time my program finds a directory, in order to call the program itself but with a new argv[2] argument (which is the current dir). I did it successfully with fork() but with pthread I've some difficulties. I don't know if I can do something like that : #include <unistd.h> #include <stdlib.h> #include <stdio.h> #include <string.h> #include <sys/types.h> #include <sys/stat.h> #include <sys/wait.h> #include <dirent.h> int main(int argc, char **argv) { pthread_t threadID[10] = {0}; DIR * dir; struct dirent * entry; struct stat status; pthread_attr_t attr; pthread_attr_init(&attr); int i = 0; char *res; char *tmp; char *file; if(argc != 3) { printf("Usage : %s <file> <dir>\n", argv[0]); exit(EXIT_FAILURE); } if(stat(argv[2],&status) == 0) { dir = opendir(argv[2]); file = argv[1]; } else exit(EXIT_FAILURE); while ((entry = readdir(dir))) { if (strcmp(entry->d_name, ".") && strcmp(entry->d_name, "..")) { tmp = malloc(strlen(argv[2]) + strlen(entry->d_name) + 2); strcpy(tmp, argv[2]); strcat(tmp, "/"); strcat(tmp, entry->d_name); stat(tmp, &status); if (S_ISDIR(status.st_mode)) { argv[2] = tmp; pthread_create( &threadID[i], &attr, execvp(argv[0], argv), NULL); printf("New thread created : %d", i); i++; } else if (!strcmp(entry->d_name, file)) { printf(" %s was found - Thread number = %d\n",tmp, i); break; } free(tmp); } } pthread_join( threadID[i] , &res ); exit(EXIT_SUCCESS); } Actually it doesn't works : pthread_create( &threadID[i], &attr, execvp(argv[0], argv), NULL); I have no runtime error, but when the file to find is in another directory, the thread is not created and so execvp(argv[0], argv) is not called... Thank you for you help, Simon

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• initializer element is not constant error.

  - by jeeva

  i am declaring cg-point or rect as const it giving above error any one help this,, #import "newViewController.h" #import "first.h" const CGPoint point=CGPointMake(50,50);

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• Why SQL2008 debugger would NOT step into a certain child stored procedure

  - by John Galt

  I'm encountering differences in T-SQL with SQL2008 (vs. SQL2000) that are leading me to dead-ends. I've verified that the technique of sharing #TEMP tables between a caller which CREATES the #TEMP and the child sProc which references it remain valid in SQL2008 See recent SO question. My core problem remains a critical "child" stored procedure that works fine in SQL2000 but fails in SQL2008 (i.e. a FROM clause in the child sProc is coded as: SELECT * FROM #AREAS A) despite #AREAS being created by the calling parent. Rather than post snippets of the code now, here is another symptom that may help you suggest something. I fired up the new debugger in SQL Mgmt Studio: EXEC dbo.AMS1 @S1='06',@C1='037',@StartDate='01/01/2008',@EndDate='07/31/2008',@Type=1,@ACReq = 1,@Output = 0,@NumofLines = 30,@SourceTable = 'P',@LoanPurposeCatg='P' This is a very large sProc and the key snippet that is weird is the following: **create table #Areas ( State char(2) , County char(3) , ZipCode char(5) NULL , CityName varchar(28) NULL , PData varchar(3) NULL , RData varchar(3) NULL , SMSA_CD varchar(10) NULL , TypeCounty varchar(50) , StateAbbr char(2) ) EXECUTE dbo.AMS_I_GetAreasV5 -- this child populates #Areas @SMSA = @SMSA , @S1 = @S1 , @C1 = @C1 , @Z1 = @Z1 , @SourceTable = @SourceTable , @CustomID = @CustomID , @UserName = @UserName , @CityName = @CityName , @Debug=0 EXECUTE dbo.AMS_I_GetAreas_FixAC -- this child cannot reference #Areas @StartDate = @StartDate , @EndDate = @EndDate , @SMSA_CD = @SMSA_CD , @S1 = @S1 , @C1 = @C1 , @Z1 = @Z1 , @CityName = @CityName , @CustomID = @CustomID , @Debug=0 -- continuation of the parent sProc** I can step through the execution of the parent stored procedure. When I get to the first child sproc above, I can either STEP INTO dbo.AMS_I_GetAreasV5 or STEP OVER its execution. When I arrive at the invocation of the 2nd child sProc - dbo.AMS_I_GetAreas_FixAC - I try to STEP INTO it (because that is where the problem statement is) and STEP INTO is ignored (i.e. treated like STEP OVER instead; yet I KNOW I pressed F11 not F10). It WAS executed however, because when control is returned to the statement after the EXECUTE, I click Continue to finish execution and the results windows shows the errors in the dbo.AMS_I_GetAreas_FixAC (i.e. the 2nd child) stored procedure. Is there a way to "pre-load" an sProc with the goal of setting a breakpoint on its entry so that I can pursue execution inside it? In summary, I wonder if the inability to step into a given child sproc might be related to the same inability of this particular child to reference a #temp created by its parent (caller).

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• Why is there no Constant keyword in Java?

  - by harigm

  I am curious learner of Java, and I was thinking about the topic of "CONSTANTS". I have learnt that Java allows us to declare constants by using final keyword. My question is why didn't Java introduce Constant (const) keyword. Since many people say it has come from C++, in C++ we have const keyword. Please share your thoughts.

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