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  • A few questions about char pointers.

    - by m4design
    1- How does this work: char *ptr = "hi"; Now the compiler will put this string in the memory (I'm guessing the stack), and create a pointer to it? Is this is how it works? 2- Also if it is created locally in a function, when the function returns will the memory occupied by the string be freed? 3- Last but not least, why is this not allowed: ptr[0] = 'H'; ?

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  • How to make a copy of a char and not a reference in C++

    - by Phenom
    If I declare a function like this: string hash (char* key) then any change I make to key will also change it's value when the function exits, correct? I want to make a copy of it in the function so that I can safely change it without changing the original value. I tried this, but it doesn't work. string temp = key; How can it be done?

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  • Pointer to auto_ptr instead of a classical double pointer

    - by Pin
    Hello. I'm quite new to smart pointers and was trying to refactor some existing code to use auto_ptr. The question I have is about double pointers and their auto_ptr equivalent, if that makes sense. I have a function that accepts a double pointer as its parameter and the function allocates resources for it: void foo ( Image** img ) { ... *img = new Image(); ...} This function is then used like this: Image* img = NULL; foo ( &img ); ... delete img; I want to use auto_ptr to avoid having to call delete explicitly. Is the following correct? void foo ( auto_ptr<Image>* img ); and then auto_ptr<Image> img = NULL; foo ( &img ); Thanks.

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  • Pointer to struct, containing pointer to an object, for which I want to call a function

    - by user1795609
    So I've created an ADT which is a singly linked list made up of nodes. These Nodes each have a pointer to an object in them called data. Class Structure { struct Node { Object *data; Node *next; }; }; Node *head; I am trying to call a function in the object, like this: head = new Node; head -> data = new Object(); head -> next = NULL; cout << head -> data.print(); I keep getting the following error at compile. error: request for member 'print' in 'head-Structure::Node::data', which is of non-class type 'Object'*

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  • return value (not a reference) from the function, bound to a const reference in the calling function

    - by brainydexter
    "If you return a value (not a reference) from the function, then bind it to a const reference in the calling function, its lifetime would be extended to the scope of the calling function." So: const BoundingBox Player::GetBoundingBox(void) { return BoundingBox( &GetBoundingSphere() ); } Returns a value of type const BoundingBox from function GetBoundingBox() Called function: (From within function Update() the following is called:) variant I: (Bind it to a const reference) const BoundingBox& l_Bbox = l_pPlayer->GetBoundingBox(); variant II: (Bind it to a const copy) const BoundingBox l_Bbox = l_pPlayer->GetBoundingBox(); Both work fine and I don't see the l_Bbox object going out of scope. (Though, I understand in variant one, the copy constructor is not called and thus is slightly better than variant II). Also, for comparison, I made the following changes. BoundingBox Player::GetBoundingBox(void) { return BoundingBox( &GetBoundingSphere() ); } with Variants: I BoundingBox& l_Bbox = l_pPlayer->GetBoundingBox(); and II: BoundingBox l_Bbox = l_pPlayer->GetBoundingBox(); The objet l_Bbox still does not out scope. So, I don't see how "bind it to a const reference in the calling function, its lifetime would be extended to the scope of the calling function", really extends the lifetime of the object to the scope of the calling function ? Am I missing something trivial here..please explain .. Thanks a lot

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  • Call a void* as a function without declaring a function pointer

    - by ToxIk
    I've searched but couldn't find any results (my terminology may be off) so forgive me if this has been asked before. I was wondering if there is an easy way to call a void* as a function in C without first declaring a function pointer and then assigning the function pointer the address; ie. assuming the function to be called is type void(void) void *ptr; ptr = <some address>; ((void*())ptr)(); /* call ptr as function here */ with the above code, I get error C2066: cast to function type is illegal in VC2008 If this is possible, how would the syntax differ for functions with return types and multiple parameters?

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  • Accessing subclass members from a superclass pointer C++

    - by Dr. Monkey
    I have an array of custom class Student objects. CourseStudent and ResearchStudent both inherit from Student, and all the instances of Student are one or the other of these. I have a function to go through the array, determine the subtype of each Student, then call subtype-specific member functions on them. The problem is, because these functions are not overloaded, they are not found in Student, so the compiler kicks up a fuss. If I have a pointer to Student, is there a way to get a pointer to the subtype of that Student? Would I need to make some sort of fake cast here to get around the compile-time error?

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  • Member Function Pointer not quite right

    - by BlackDuck
    I have a SpecialisedRedBlackTree class that is templated. My Month class is not. In my Month class I have a private member which is an instance of SpecialisedRedBlackTree: SpecialisedRedBlackTree<Day> m_windSpeedTree; As you can see it will take the Day class/object (please correct me on any terms I get wrong). In my Month class, I have a method passing a method function pointer to this method: bool Month::CompareWindSpeed(Day a, Day b) { return ( a.GetData(WIND_SPEED_CODE) < b.GetData(WIND_SPEED_CODE)? true : false); } bool (Month::*myFuncPtr)(Day, Day); myFuncPtr = &Month::CompareWindSpeed; m_windSpeedTree.Insert(dayReading, myFuncPtr); But because I am passing a bool (Day, Day) pointer to a templated class expecting bool (T, T) T being part of this .... template Error 1 error C2664: 'SpecialisedRedBlackTree<T>::Insert' : cannot convert parameter 2 from 'bool (__thiscall Month::* )(Day,Day)' to 'bool (__cdecl *)(T,T)' Any advice?

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  • Mallocing an unsigned char array to store ints

    - by Max Desmond
    I keep getting a segmentation fault when i test the following code. I am currently unable to find an answer after having searched the web. a = (byte *)malloc(sizeof(byte) * x ) ; for( i = 0 ; i < x-1 ; i++ ) { scanf("%d", &y ) ; a[i] = y ; } Both y and x are initialized. X is the size of the array determined by the user. The segmentation fault is on the second to last integer to be added, i found this by adding printf("roar") ; before setting a[i] to y and entering one number at a time. Byte is a typedef of an unsigned char. Note: I've also tried using a[i] = (byte)y ; A is ininitalized as follows byte *a ; If you need to view the entire code it is this: #include <stdio.h> #include <stdlib.h> #include "sort.h" int p_cmp_f () ; int main( int argc, char *argv[] ) { int x, y, i, choice ; byte *a ; while( choice !=2 ) { printf( "Would you like to sort integers?\n1. Yes\n2. No\n" ) ; scanf("%d", &choice ) ; switch(choice) { case 1: printf( "Enter the length of the array: " ) ; scanf( "%d", &x ) ; a = (byte *)malloc(sizeof( byte ) * x ) ; printf( "Enter %d integers to add to the array: ", x ) ; for( i = 0 ; i < x -1 ; i++ ) { scanf( "%d", &y ) ; a[i] = y ; } switch( choice ) { case 1: bubble_sort( a, x, sizeof(int), p_cmp_f ) ; for( i = 0 ; i < x ; i++ ) printf( "%d", a[i] ; break ; case 2: selection_sort( a, x, sizeof(int), p_cmp_f ) ; for( i = 0 ; i < x; i++ ) printf( "%d", a[i] ; break ; case 3: insertion_sort( a, x, sizeof(int), p_cmp_f ) ; for( i = 0 ; i < x ; i++ ) printf( "%d", a[i] ; break ; case 4: merge_sort( a, x, sizeof(int), p_cmp_f ) ; for( i = 0 ; i < x ; i++ ) printf( "%d", a[i] ; break ; case 5: quick_sort( a, x, sizeof(int), p_cmp_f ) ; for( i = 0 ; i < x ; i++ ) printf( "%d", a[i] ; break ; default: printf("Enter either 1,2,3,4, or 5" ) ; break ; } case 2: printf( "Thank you for using this program\n" ) ; return 0 ; break ; default: printf( "Enter either 1 or 2: " ) ; break ; } } free(a) ; return 0 ; } int p_cmp_f( byte *element1, byte *element2 ) { return *((int *)element1) - *((int *)element2) ; }

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  • Can I catch bad pointer errors in C++?

    - by Simon
    Hi there, I was wondering if there is a possibility to catch errors like this in C++: object* p = new object; delete p; delete p; //this would cause an error, can I catch this? Can I check if the pointer is valid? Can I catch some exception? I know I could set the pointer p to NULL after the first object deletion. But just imagine you wouldn't do that. I am using VC++ with Visual Studio 2008/2010. Thank you

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  • Java: Checking contents of char variable with if condition

    - by Troy
    Hello, I have a char variable that is supposed to contain either a Y,y,n or N character, I want to test if it does not contain it, then display an error message and exit the program. This is the code I am using; if (userDecision != 'Y' || userDecision != 'y' || userDecision != 'n' || userDecision != 'N') { System.out.println("Error: invalid input entered for the interstate question"); System.exit(0); } Irregardless of what is in the variable it always returns true and executes the command to exit the program, what am I doing wrong?

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  • How do I convert a single char in string to an int

    - by Guest
    Keep in mind, if you choose to answer the question, I am a beginner in the field of programming and may need a bit more explanation than others as to how the solutions work. Thank you for your help. My problem is that I am trying to do computations with parts of a string (consisting only of numbers), but I do not know how to convert an individual char to an int. The string is named "message". for (int place = 0; place < message.size(); place++) { if (secondPlace == 0) { cout << (message[place]) * 100 << endl; } } Thank you.

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  • C++ sort array of char pointes

    - by user69514
    Can you tell me what's wrong with my method? I ends up putting the same thing everywhre and it's actually not sorting. void sortArrays(){ int i, j; for(i=0; i<counter; i++){ for( j=0; j<i; j++){ if( strcmp(title_arr[i], title_arr[j]) < 0){ char* title_temp = title_arr[i]; title_arr[j] = title_temp; } } }

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  • C++ sort array of char pointers

    - by user69514
    Can you tell me what's wrong with my method? I ends up putting the same thing everywhre and it's actually not sorting. void sortArrays(){ int i, j; for(i=0; i<counter; i++){ for( j=0; j<i; j++){ if( strcmp(title_arr[i], title_arr[j]) < 0){ char* title_temp = title_arr[i]; title_arr[j] = title_temp; } } }

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  • Check and avoid if a char is being entered in a int

    - by John
    Hi.... This is a exremely stupid question but i need help with this.... I'm trying to make a small program that i made robust and needed some help with tht.... int num1; int num2 = 0; System.out.print("Enter number 1: "); num1 = kb.nextInt(); while(num2<num1) { System.out.print("Enter number 2: "); num2 = kb.nextInt(); } Number 2 has to be greater than number 1 Also i want the program to automatically check and ignore if the user enters a char instead of an int... Cause right now when a user enters lets say "r" instead of a number the program just exists....

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  • char '0x8' what character is this?

    - by OHHAI
    I have a large amount of data in a database. When I attempt to read a certain portion of the data and generate some xml and send it to a webservice I get the following exception... The char '0x8' in 'java.lang.IllegalArgumentException'. I'm guessing it is some bad data, as it has worked perfectly for about 7 months but now some user uploaded some new data that seems to have some issues. Anyone know what character this is so I can just run a sql query and clean it from the db? Thanks in advance.

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  • How to convert char to LPCTSTR (MFC)?

    - by Shark
    Is there any way to do this? This is what I am trying to do: char s[] = { 'a', 'b' }; label.SetWindowTextW(s[1]); label is CStatic typed, _UNICODE is defined. Any help would be appreciated. UPD: Tried to use CString(s[1]), it works for ASCII characters but others won't work. E. g. for the ? it returns |.

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  • fill a buffer successively

    - by mkind
    i intend to fill a char-pointer array successively in a for-loop. the content to fill in is a integer so i need to cast. but i didn't get the result i want to.. for (i=0;i<max0;i++){ sprintf(buf, "%d", content[i]); } sprintf replaces the hole buf, but i want to append. for (i=0;i<max0;i++){ buf[i]=(char) contint[i] } but this isn't working too. it seems to me, i get ascii-code of the content[i].

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  • Passing char * into fopen with C.

    - by Rhys
    Hey there, I'm writing a program that passes data from a file into an array, but I'm having trouble with fopen (). It seems to work fine when I hardcode the file path into the parameters (eg fopen ("data/1.dat", "r");) but when I pass it as a pointer, it returns NULL. Note that line 142 will print "data/1.dat" if entered from command line so parse_args () appears to be working. 132 int 133 main(int argc, char **argv) 134 { 135 FILE *in_file; 136 int *nextItem = (int *) malloc (sizeof (int)); 137 set_t *dictionary; 138 139 /* Parse Arguments */ 140 clo_t *iopts = parse_args(argc, argv); 141 142 printf ("INPUT FILE: %s.\n", iopts->input_file); /* This prints correct path */ 143 /* Initialise dictionary */ 144 dictionary = set_create (SET_INITAL_SIZE); 145 146 /* Use fscanf to read all data values into new set_t */ 147 if ((in_file = fopen (iopts->input_file, "r")) == NULL) 148 { 149 printf ("File not found...\n"); 150 return 0; 151 } Thanks! Rhys

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  • Calling a method on an unitialized object (null pointer)

    - by Florin
    What is the normal behavior in Objective-C if you call a method on an object (pointer) that is nil (maybe because someone forgot to initialize it)? Shouldn't it generate some kind of an error (segmentation fault, null pointer exception...)? If this is normal behavior, is there a way of changing this behavior (by configuring the compiler) so that the program raises some kind of error / exception at runtime? To make it more clear what I am talking about, here's an example. Having this class: @interface Person : NSObject { NSString *name; } @property (nonatomic, retain) NSString *name; - (void)sayHi; @end with this implementation: @implementation Person @synthesize name; - (void)dealloc { [name release]; [super dealloc]; } - (void)sayHi { NSLog(@"Hello"); NSLog(@"My name is %@.", name); } @end Somewhere in the program I do this: Person *person = nil; //person = [[Person alloc] init]; // let's say I comment this line person.name = @"Mike"; // shouldn't I get an error here? [person sayHi]; // and here [person release]; // and here

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