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  • How to get this to compile?

    - by ShaChris23
    I have this code which compiles and works as expected: class Right {}; class Left { public: Left& operator = (Right const&) { //... Do something ... return *this; } }; int main() { Right right; Left left; // Assign individual object -- this works left = right; } But now, this one surprises me, I thought the template would work itself out since I already provided the = operator() to the Left class. int main() { ... std::list<Right> rightLst; std::list<Left> leftLst; // Assign a list of objects -- this doesn't compile leftLst = rightLst; } What can I do so that I could convert the rightLst to leftLst conversion in a single line?

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  • Objective C LValue required as unary '&' operand

    - by Bob
    Hello! In my code, I get this error when I try to get a pointer to my class property. (I wrote a small *.OBJ file translator in Python, discarding the normals) CODE: //line: line of text const char *str = [line UTF8String]; Point3D *p1, *p2, *p3; p1 = [Point3D makeX:0 Y:0 Z:0]; p2 = [Point3D makeX:0 Y:0 Z:0]; p3 = [Point3D makeX:0 Y:0 Z:0]; sscanf(str, "t %f,%f,%f %f,%f,%f %f,%f,%f",(&[p1 x]),&([p1 y]),&([p1 z]),&([p2 x]),&([p2 y]),&([p2 z]),&([p3 x]),&([p3 y]),&([p3 z])); Triangle3D *tri = [Triangle3D make:p1 p2:p2 p3:p3];

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  • Linq to SQL Strange SQL Translation

    - by Master Morality
    I have a simple query that is generating some odd SQL translations, which is blowing up my code when the object is saturated. from x in DataContext.MyEntities select new { IsTypeCDA = x.EntityType == "CDA" //x.EntityType is a string and EntityType.CDA is a const string... } I would expect this query should translate to: SELECT (CASE WHEN [t0].[EntityType] = @p1 THEN 1 ELSE 0 END) as [IsTypeCDA] ... Instead I get this : SELECT (CASE WHEN @p1 = [t0].[EntityType] THEN 1 WHEN NOT (@p1 = [t0].[EntityType]) THEN 0 ELSE NULL END) AS [IsTypeCDA] ... Since I'm saturating a POCO where IsTypeCDA is a bool, it blows up stating I can't assign null to bool. Any thoughts? Edit: fixed the property names so they make sense...

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  • When should an array name be treated as a pointer and when does it just represent the array itself? [duplicate]

    - by user1087373
    This question already has an answer here: When is an array name or a function name 'converted' into a pointer ? (in C) 4 answers I just made a test program after reading the book and the result turned out confusing: #include <stdio.h> int main(void) { char text[] = "hello!"; printf("sizeof(text):%d sizeof(text+2):%d sizeof(text[0]):%d \n",(int)sizeof(text), sizeof(text+2), sizeof(text[0])); printf("text:%p sizeof(text):%d &text:%p sizeof(&text):%d \n",text, sizeof(text), &text, sizeof(&text)); printf("text+1:%p &text+1:%p \n", text+1, &text+1); return 0; } The result: sizeof(text):7 sizeof(text+2):4 sizeof(text[0]):1 text:0xbfc8769d sizeof(text):7 &text:0xbfc8769d sizeof(&text):4 text+1:0xbfc8769e &text+1:0xbfc876a4 What makes me feel confused are: why the value of 'sizeof(text)' is 7 whereas 'sizeof(text+2)' is 4 what's the difference between 'text' and '&text'?

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  • incorrect variable value outside main()

    - by cru3l
    i have this code #import <Foundation/Foundation.h> int testint; NSString *teststring; int Test() { NSLog(@"%d",testint); NSLog(@"%@",teststring); } int main (int argc, const char * argv[]) { NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init]; testint = 5; NSString *teststring = [[NSString alloc] initWithString:@"test string"]; Test(); [pool drain]; return 0; } in output i have: 5 (null) why Test function doesn't see correct teststring value? What should I do, to have correct "test string" in output?

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  • So, I guess I can't use "&&" in the Python if conditional. Any help?

    - by Sergio Tapia
    Here's my code: # F. front_back # Consider dividing a string into two halves. # If the length is even, the front and back halves are the same length. # If the length is odd, we'll say that the extra char goes in the front half. # e.g. 'abcde', the front half is 'abc', the back half 'de'. # Given 2 strings, a and b, return a string of the form # a-front + b-front + a-back + b-back def front_back(a, b): # +++your code here+++ if len(a) % 2 == 0 && len(b) % 2 == 0: return a[:(len(a)/2)] + b[:(len(b)/2)] + a[(len(a)/2):] + b[(len(b)/2):] else: #todo! Not yet done. :P return I'm getting an error in the IF conditional. What am I doing wrong?

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  • c++/cli pass (managed) delegate to unmanaged code

    - by Ron Klein
    How do I pass a function pointer from managed C++ (C++/CLI) to an unmanaged method? I read a few articles, like this one from MSDN, but it describes two different assemblies, while I want only one. Here is my code: 1) Header (MyInterop.ManagedCppLib.h): #pragma once using namespace System; namespace MyInterop { namespace ManagedCppLib { public ref class MyManagedClass { public: void DoSomething(); }; }} 2) CPP Code (MyInterop.ManagedCppLib.cpp) #include "stdafx.h" #include "MyInterop.ManagedCppLib.h" #pragma unmanaged void UnmanagedMethod(int a, int b, void (*sum)(const int)) { int result = a + b; sum(result); } #pragma managed void MyInterop::ManagedCppLib::MyManagedClass::DoSomething() { System::Console::WriteLine("hello from managed C++"); UnmanagedMethod(3, 7, /* ANY IDEA??? */); } I tried creating my managed delegate and then I tried to use Marshal::GetFunctionPointerForDelegate method, but I couldn't compile.

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  • Usage of atoi in the c language

    - by maddy
    I don't understand the results of the following C code. main() { char s[] = "AAA"; advanceString(s); } void advanceString(p[3]) { int val = atoi(p); printf("The atoi val is %d\n",val); } Here the atoi val is shown as 0. But I could not figure out the exact reason. As per my understanding, it should be the summation of decimal equivalent of each values in the array.? Please correct me if I am wrong.

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  • How do I use "this" in a member function?

    - by Peter Stewart
    I've written a member function of class Node to read a tree of Nodes in postfix order. It will be called by the Node instance which is the root node of the tree. So: N.postfix(); these appear to be illeagal: *this->left.postfix(); *this->right.postfix(); What is the proper way to do this? class Node { public: const char *cargo; int depth; Node *left; Node *right void Node::postfix() { if (this==__nullptr) { return; } else { *this->left.postfix(); *this->right.postfix(); out<<*this->cargo<<"\n"; return; } };

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  • RSA encrypted data block size

    - by calccrypto
    how do you store an rsa encrypted data block? the output might be significantly greater than the original input data block size, and i dont think people waste memory by padding bucket loads of 0s in front of each data block. besides, how would they be removed? or is each block stored on new lines within the file? if that is the case, how would you tell the difference between legitimate new line and a '\n' char written into the file? what am i missing? im writing the "write to file" part in python, so maybe its one of the differences between: open(file,'w') open(file,'w+b') open(file,'wb') that i dont know. or is it something else?

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  • parsing/matching string occurrence in C

    - by David
    I have the following string: const char *str = "\"This is just some random text\" 130 28194 \"Some other string\" \"String 3\"" I would like to get the the integer 28194 of course the integer varies, so I can't do strstr("20194"). So I was wondering what would be a good way to get that part of the string? I was thinking to use #include <regex.h> which I already have a procedure to match regexp's but not sure how the regexp in C will look like using the POSIX style notation. [:alpha:]+[:digit:] and if performance will be an issue. Or will it be better using strchr,strstr? Any ideas will be appreciate it

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  • Empty Structures compile in VB 10+

    - by Mark Hurd
    This is at least a documentation error, if not a bug. In VB.NET prior to .NET 4.0 (i.e. VB.NET 7 through 9) an empty Structure declaration fails at compile-time with error BC30281: Structure 'MySimpleEmpty' must contain at least one instance member variable or Event declaration. E.g. The following two structures compile successfully in VB10, and not prior: Structure MySimpleEmpty End Structure Public Structure AnotherEmpty Public Const StillEmpty As Boolean = True End Structure I note the documentation for the Error BC30281 stops at VB9, but the documentation for the Structure statement still has the datamemberdeclarations as required even as of VB11 (.NET 4.5 VS2012). These two Structures compile in VB11 (VS2012) as well. (Thanks John Woo.) Is there some blog entry or documentation confirming this is an intended change or a bug in VB10 and later?

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  • Using charAt in java

    - by ThuL?nå F?rñ?nDö
    This is my assignment: Write a program where the user enters a string, and the program echoes it to the monitor with one character per line: C:\>java LinePerChar Enter a string: Octopus O c t o p u s I have tried, but I'm getting some compilation errors. Here's my code: import java.util.*; class CharactorEcho{ public static void main(String args []){ Scanner sc = new Scanner(System.in); System.out.println("Enter a string :"); try { String inputString = sc.nextLine(); for(int i=0; i < sc.length(); i++) { char c = inputString.charAt(i); System.out.println("" + c); } } catch(IOException e) { } } }

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  • Why is this c++ string concatenation missing a space?

    - by danutenshu
    I am working with c++ strings, and am a beginner at programming. I am expecting: 99 Red Balloons But I am receiving: 99 RedBalloons Why is that? #include <string> #include <iostream> using namespace std; int main() { string text = "9"; string term( "9 "); string info = "Toys"; string color; char hue[4] = {'R','e','d','\0'}; color = hue; info = "Balloons"; text += (term + color + info); cout << endl << text << endl; return 0; }

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  • Unit testing with serialization mock objects in C++

    - by lhumongous
    Greetings, I'm fairly new to TDD and ran across a unit test that I'm not entirely sure how to address. Basically, I'm testing a couple of legacy class methods which read/write a binary stream to a file. The class functions take a serializable object as a parameter, which handles the actual reading/writing to the file. For testing this, I was thinking that I would need a serialization mock object that I would pass to this function. My initial thought was to have the mock object hold onto a (char*) which would dynamically allocate memory and memcpy the data. However, it seems like the mock object might be doing too much work, and might be beyond the scope of this particular test. Is my initial approach correct, or can anyone think of another way of correctly testing this? Thanks!

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  • Memory leak till crash due to HttpRequest

    - by Alex R.
    I played with HttpRequest and realized that the memory is not cleaned up after any request. After some time the running tab within Chrome will crash. Here is some testing code. Put a large sized file into the 'www' directory and set the URL in the code accordingly. import 'dart:async'; import 'dart:html'; void main() { const PATH = "http://127.0.0.1:3030/PATH_TO_FILE"; new Timer.periodic(new Duration(seconds:10), (Timer it)=>getString(PATH)); } void getString( String url){ HttpRequest.getString(url).then((String data){ }); } Is this really a bug or did I something wrong?

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  • reading a file that doesn't exist

    - by John
    Hi, I have got a small program that prints the contents of files using the system call - read. unsigned char buffer[8]; size_t offset=0; size_t bytes_read; int i; int fd = open(argv[1], O_RDONLY); do{ bytes_read = read(fd, buffer, sizeof(buffer)); printf("0x%06x : ", offset); for(i=0; i<bytes_read; ++i) { printf("%c ", buffer[i]); } printf("\n"); offset = offset + bytes_read; }while(bytes_read == sizeof(buffer)); Now while running I give a file name that doesn't exist. It prints some kind of data mixed with environment variables and a segmentation fault at the end. How is this possible? What is the program printing? Thanks, John

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  • How to print an isosceles triangle

    - by Steve
    Hello, I'm trying to learn programming by myself, I'm working from a book that has the following problem which I can't solve: Allow the user to input two values: a character to be used for printing an isosceles triangle and the size of the peak for the triangle. For example, if the user inputs # for the character and 6 for the peak, you should produce the following display: # ## ### #### ##### ###### ##### #### ### ## # This is the code I've got so far: char character; int peak; InputValues(out character, out peak); for (int row = 1; row < peak * 2; row++) { for (int col = 1; col <= row; col++) { Console.Write(character); } Console.WriteLine(); } Console.Read() // hold console open Thanks in advance.

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  • Why would I get a bus error or segmentation fault when calling free() normally?

    - by chucknelson
    I have a very simple test program, running on Solaris 5.8: #include <stdio.h> #include <stdlib.h> int main(void) { char *paths; paths = getenv("PATH"); printf("Paths: %s\n", paths); free(paths); // this causes a bus error return 0; } If I don't call free() at the end, it displays the message fine and exits. If I include the free() call, it crashes with a bus error. I've had other calls to free(), in other programs, cause segmentation faults as well. Even if I allocate the memory for *paths myself, free() will cause a bus error. Is there some reason trying to free up the memory is causing a crash?

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  • Using memory mapping in C for reading binary

    - by user1320912
    I am trying to read data from a binary file and process it.It is a very large file so I thought I would use memory mapping. I am trying to use memory mapping so I can read the file byte by byte. I am getting a few compiler errors while doing this. I am doing this on a linux platform #include <unistd.h> #include <sys/types.h> #include <sys/mman.h> int fd; char *data; fd = open("data.bin", O_RDONLY); pagesize = 4000; data = mmap((caddr_t)0, pagesize, PROT_READ, MAP_SHARED, fd, pagesize); The errors i get are : caddr not initialized, R_RDONLY not initialized, mmap has too few arguments. Could someone help me out ?

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  • usage of 2 charectors in single qoutes in c

    - by user1632141
    #include<stdio.h> int main() { char ch = 'A'; printf("%d\n",'ag'); printf("%d\n",'a'); printf("%d, %d, %d, %d", sizeof(ch), sizeof('a'), sizeof('Ag'), sizeof(3.14f)); return 0; } I used to have many doubts on the output of this question while running on g++ and gcc. But I have cleared almost all the doubts by referring these links: Single and double quotes in C/C++ Single quotes vs. double quotes in C I still need to understand one thing about the output of this question. Can someone please explain the output of printf("%d\n",'ag'); mentioned above in the program. How is it actually stored in the memory? The output for the program on the Linux/GCC platform is: 24935 97 1, 4, 4, 4

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  • Operator + for matrices in C++

    - by cibercitizen1
    I suppose the naive implementation of a + operator for matrices (2D for instance) in C++ would be: class Matrix { Matrix operator+ (Matrix other) const { Matrix result; // fill result with *this.data plus other.data return result; } } so we could use it like Matrix a; Matrix b; Matrix c; c = a + b; Right? But if matrices are big this is not efficient as we are doing one not-necessary copy (return result). Therefore, If we wan't to be efficient we have to forget the clean call: c = a + b; Right? What would you suggest / prefer ? Thanks.

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  • Reducing template bloat with inheritance

    - by benoitj
    Does anyone have experience reducing template code bloat using inheritance? i hesitate rewriting our containers this way: class vectorBase { public: int size(); void clear(); int m_size; void *m_rawData; //.... }; template< typename T > class vector : public vectorBase { void push_back( const T& ); //... }; I should keep maximum performance while reducing compile time I'm also wondering why stl implementations do not uses this approach Thanks for your feedbacks

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  • assignment vs std::swap and merging and keeping duplicates in seperate object

    - by rubenvb
    Say I have two std::set<std::string>s. The first one, old_options, needs to be merged with additional options, contained in new_options. I can't just use std::merge (well, I do, but not only that) because I also check for doubles and warn the user about this accordingly. To this effect, I have void merge_options( set<string> &old_options, const set<string> &new_options ) { // find duplicates and create merged_options, a stringset containing the merged options // handle duplicated the way I want to // ... old_options = merged_options; } Is it better to use std::swap( merged_options, old_options ); or the assignment I have? Is there a better way to filter duplicates and return the merged set than consecutive calls to std::set_intersection and std::set_union to detect dupes and merge the sets? I know it's slower than one traversal and doing both at once, but these sets are small (performance is not critical) and I trust the Standard more than I trust myself.

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  • SQLite SQLite column can't be updated to any value but zero (real type)

    - by user1065320
    Hi I'm trying to create a three fields table (date,text,real), I can insert and update the first two fields but can't set or update the last one. createSQL = @"CREATE TABLE IF NOT EXISTS ACTIVITIES (MYDATE DATETIME PRIMARY KEY, ACTIVITY TEXT , LENGTH REAL);"; try to insert char *update = "INSERT OR REPLACE INTO ACTIVITIES (MYDATE, ACTIVITY , LENGTH) VALUES (?, ? ,?);"; sqlite3_stmt *stmt; if (sqlite3_prepare_v2(database, update , -1, &stmt, nil) == SQLITE_OK) { sqlite3_bind_double(stmt, 1, valueToWrite); sqlite3_bind_text(stmt, 2, [task UTF8String], -1, NULL); sqlite3_bind_double(stmt, 3, 1.5); } if (sqlite3_step(stmt) != SQLITE_DONE) { NSAssert1(0, @"Error updating table: %s", errorMsg); } sqlite3_finalize(stmt); sqlite3_close(database); The first two values are updated but the last one remains 0 even if I'm writing a value like 1.5 or put a double variable with a different value Thanks

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