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  • should std::auto_ptr<>::operator = reset / deallocate its existing pointee ?

    - by afriza
    I read here about std::auto_ptr<::operator= Notice however that the left-hand side object is not automatically deallocated when it already points to some object. You can explicitly do this by calling member function reset before assigning it a new value. However, when I read the source code for header file C:\Program Files\Microsoft Visual Studio 8\VC\ce\include\memory template<class _Other> auto_ptr<_Ty>& operator=(auto_ptr<_Other>& _Right) _THROW0() { // assign compatible _Right (assume pointer) reset(_Right.release()); return (*this); } auto_ptr<_Ty>& operator=(auto_ptr<_Ty>& _Right) _THROW0() { // assign compatible _Right (assume pointer) reset(_Right.release()); return (*this); } auto_ptr<_Ty>& operator=(auto_ptr_ref<_Ty> _Right) _THROW0() { // assign compatible _Right._Ref (assume pointer) _Ty **_Pptr = (_Ty **)_Right._Ref; _Ty *_Ptr = *_Pptr; *_Pptr = 0; // release old reset(_Ptr); // set new return (*this); } What is the correct/standard behavior? How do other STL implementations behave?

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  • How to do pointer work with accessor methods in Objective-C

    - by Jasconius
    Basic problem statement: I have a very good reason for doing some pointer fanciness in an app where I need to pass a decimal by reference. So I have a class which stores many a decimal, so let's say is has a property as such: @property (nonatomic) double myDecimalValue; I want to pass it by reference to some other class. [someOtherObject sendMyDecimalByReference:&myDecimalValue]; But, a problem emerges! The way that actually has to be written (because it's a property) is [someOtherObject sendMyDecimalByReference:&decimalOrigin.myDecimalValue]; This fails to compile in objective-c I get around it by writing the following - (double *) myDecimalValueRef; [someOtherObject sendMyDecimalByReference:[decimalOrigin myDecimalValue]]; Except I have dozens of these decimals and I don't want to write that stupid wrapper function for every value. Is there a shorthand way to do this in Objective-C using just the Getter functions? Let's just assume I have a great reason for not using NSNumber. Thanks!

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  • Bit shift and pointer oddities in C, looking for explanations

    - by foo
    Hi all, I discovered something odd that I can't explain. If someone here can see what or why this is happening I'd like to know. What I'm doing is taking an unsigned short containing 12 bits aligned high like this: 1111 1111 1111 0000 I then want to shif the bits so that each byte in the short hold 7bits with the MSB as a pad. The result on what's presented above should look like this: 0111 1111 0111 1100 What I have done is this: unsigned short buf = 0xfff; //align high buf <<= 4; buf >>= 1; *((char*)&buf) >>= 1; This gives me something like looks like it's correct but the result of the last shift leaves the bit set like this: 0111 1111 1111 1100 Very odd. If I use an unsigned char as a temporary storage and shift that then it works, like this: unsigned short buf = 0xfff; buf <<= 4; buf >>= 1; tmp = *((char*)&buf); *((char*)&buf) = tmp >> 1; The result of this is: 0111 1111 0111 1100 Any ideas what is going on here?

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  • A queue in C using structs and dynamic memory allocation (linked list)

    - by Martin Pugh
    I am tasked with making a queue data structure in C, as a linked list. Our lecturer gave us a large amount of code to implement a stack, but we have to adapt it to create a queue. The code our lecturer gave us ends up not compiling and segfaulting at the exact same point as the code I wrote for the queue. I'm very new to structs, malloc and C in general, so there could be something painfully obvious I've overlooked. Here is the code I am using: #include <stdio.h> #include <stdlib.h> struct node{ int data; //contains the actual data struct node *prev; //pointer to previous node (Closer to front) struct node *next; //pointer to next node (Closer to back) }; typedef struct node *Nodepointer; struct queue{ Nodepointer front; Nodepointer back; }; typedef struct queue *Queuepointer; main(){ Queuepointer myqueue; //create a queue called myqueue init(myqueue); //initialise the queue Nodepointer new = (Nodepointer)malloc(sizeof(struct node)); myqueue->front = new; } int init(Queuepointer q){ q = (Queuepointer)malloc(sizeof(struct queue)); q->front = NULL; q->back = NULL; } The idea is that the queue struct 'contains' the first and last nodes in a queue, and when a node is created, myqueue is updated. However, I cannot even get to that part (pop and push are written but omitted for brevity). The code is segfaulting at the line myqueue->front = new; with the following gdb output: Program received signal SIGSEGV, Segmentation fault. 0x08048401 in main () at queue.c:27 27 myqueue->front = new; Any idea what I'm doing wrong?

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  • C++ -- Is there an implicit cast here from Fred* to auto_ptr<Fred>?

    - by q0987
    Hello all, I saw the following code, #include <new> #include <memory> using namespace std; class Fred; // Forward declaration typedef auto_ptr<Fred> FredPtr; class Fred { public: static FredPtr create(int i) { return new Fred(i); // Is there an implicit casting here? If not, how can we return // a Fred* with return value as FredPtr? } private: Fred(int i=10) : i_(i) { } Fred(const Fred& x) : i_(x.i_) { } int i_; }; Please see the question listed in function create. Thank you // Updated based on comments Yes, the code cannot pass the VC8.0 error C2664: 'std::auto_ptr<_Ty::auto_ptr(std::auto_ptr<_Ty &) throw()' : cannot convert parameter 1 from 'Fred *' to 'std::auto_ptr<_Ty &' The code was copied from the C++ FAQ 12.15. However, after making the following changes, replace return new Fred(i); with return auto_ptr<Fred>(new Fred(i)); This code can pass the VC8.0 compiler. But I am not sure whether or not this is a correct fix.

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  • Getting the start address of the current process's heap?

    - by beta
    Hey, I am exploring the lower level workings of the system, and was wondering how malloc determines the start address of the heap. Is the heap a constant offset or is there a call of some sort to get the start address? Does the stack effect the start address of the heap? Thanks, Braden McDorman

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  • Pointer initialization doubt

    - by Jestin Joy
    We could initialize a character pointer like this in C. char *c="test"; Where c points to the first character(t). But when I gave code like below. It gives segmentation fault. #include<stdio.h> #include<stdlib.h> main() { int *i=0; printf("%d",*i); } Also when I give #include<stdio.h> #include<stdlib.h> main() { int *i; i=(int *)malloc(2); printf("%d",*i); } It worked(gave output 0). When I gave malloc(0), it worked(gave output 0). Please tell what is happening

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  • What's correct way to remove a boost::shared_ptr from a list?

    - by Catskul
    I have a std::list of boost::shared_ptr<T> and I want to remove an item from it but I only have a pointer of type T* which matches one of the items in the list. However I cant use myList.remove( tPtr ) I'm guessing because shared_ptr does not implement == for its template argument type. My immediate thought was to try myList.remove( shared_ptr<T>(tPtr) ) which is syntactically correct but it will crash from a double delete since the temporary shared_ptr has a separate use_count. std::list< boost::shared_ptr<T> > myList; T* tThisPtr = new T(); // This is wrong; only done for example code. // stand-in for actual code in T using // T's actual "this" pointer from within T { boost::shared_ptr<T> toAdd( tThisPtr ); // typically would be new T() myList.push_back( toAdd ); } { //T has pointer to myList so that upon a certain action, // it will remove itself romt the list //myList.remove( tThisPtr); //doesn't compile myList.remove( boost::shared_ptr<T>(tThisPtr) ); // compiles, but causes // double delete } The only options I see remaining are to use std::find with a custom compare, or to loop through the list brute force and find it myself, but it seems there should be a better way. Am I missing something obvious, or is this just too non-standard a use to be doing a remove the clean/normal way?

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  • C: How come an array's address is equal to its value?

    - by Alexandre
    In the following bit of code, pointer values and pointer addresses differ as expected. But array values and addresses don't! How can this be? Output my_array = 0022FF00 &my_array = 0022FF00 pointer_to_array = 0022FF00 &pointer_to_array = 0022FEFC ... #include <stdio.h> int main() { char my_array[100] = "some cool string"; printf("my_array = %p\n", my_array); printf("&my_array = %p\n", &my_array); char *pointer_to_array = my_array; printf("pointer_to_array = %p\n", pointer_to_array); printf("&pointer_to_array = %p\n", &pointer_to_array); printf("Press ENTER to continue...\n"); getchar(); return 0; }

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  • Operator precedence and struct definition in C

    - by Yktula
    struct struct0 { int a; }; struct struct1 { struct struct0 structure0; int b; } rho; &rho->structure0; /* Reference 1 */ (struct struct0 *)rho; /* Reference 2 */ (struct struct0)rho; /* Reference 3 */ From reference 1, does the compiler take the address of rho, and then access structure0, or vice-versa? What does the line at reference 2 do? Since structure0 is the first member of struct1, would reference 3 be equivalent to reference 1?

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  • Deleting a non-owned dynamic array through a pointer

    - by ayanzo
    Hello all, I'm relatively novice when it comes to C++ as I was weened on Java for much of my undergraduate curriculum (tis a shame). Memory management has been a hassle, but I've purchased a number books on ansi C and C++. I've poked around the related questions, but couldn't find one that matched this particular criteria. Maybe it's so obvious nobody mentions it? This question has been bugging me, but I feel as if there's a conceptual point i'm not utilizing. Suppose: char original[56]; cstr[0] = 'a'; cstr[1] = 'b'; cstr[2] = 'c'; cstr[3] = 'd'; cstr[4] = 'e'; cstr[5] = '\0'; char *shaved = shavecstr(cstr); delete[] cstrn; where char* shavecstr(char* cstr) { size_t len = strlen(cstr); char* ncstr = new char[len]; strcpy(ncstr,cstr); return ncstr; } In that the whole point is to have 'original' be a buffer that fills with characters and routinely has its copy shaved and used elsewhere. To prevent leaks, I want to free up the memory held by 'shaved' to be used again after it passes through some arguments. There is probably a good reason for why this is restricted, but there should be some way to free the memory as by this configuration, there is no way to access the original owner (pointer) of the data.

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  • Does C99 guarantee that arrays are contiguous ?

    - by kriss
    Following an hot comment thread in another question, I came to debate of what is and what is not defined in C99 standard about C arrays. Basically when I define a 2D array like int a[5][5], does the standard C99 garantee or not that it will be a contiguous block of ints, can I cast it to (int *)a and be sure I will have a valid 1D array of 25 ints. As I understand the standard the above property is implicit in the sizeof definition and in pointer arithmetic, but others seems to disagree and says casting to (int*) the above structure give an undefined behavior (even if they agree that all existing implementations actually allocate contiguous values). More specifically, if we think an implementation that would instrument arrays to check array boundaries for all dimensions and return some kind of error when accessing 1D array, or does not give correct access to elements above 1st row. Could such implementation be standard compilant ? And in this case what parts of the C99 standard are relevant.

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  • How to convert struct to char array in C

    - by falcojr
    I'm trying to convert a struct to a char array to send over the network. However, I get some weird output from the char array when I do. #include <stdio.h> struct x { int x; } __attribute__((packed)); int main() { struct x a; a.x=127; char *b = (char *)&a; int i; for (i=0; i<4; i++) printf("%02x ", b[i]); printf("\n"); for (i=0; i<4; i++) printf("%d ", b[i]); printf("\n"); return 0; } Here is the output for various values of a.x (on an X86 using gcc): 127: 7f 00 00 00 127 0 0 0 128: ffffff80 00 00 00 -128 0 0 0 255: ffffffff 00 00 00 -1 0 0 0 256: 00 01 00 00 0 1 0 0 I understand the values for 127 and 256, but why do the numbers change when going to 128? Why wouldn't it just be: 80 00 00 00 128 0 0 0 Am I forgetting to do something in the conversion process or am I forgetting something about integer representation? *Note: This is just a small test program. In a real program I have more in the struct, better variable names, and I convert to little-endian. *Edit: formatting

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  • Whats the problem with int *p; *p=23;

    - by piemesons
    Yesterday in my interview I was asked this question. (At that time I was highly pressurized by so many abrupt questions). int *p; *p=23; printf('%d',*p); Is there any problem with this code? I explained him that you are trying to assign value to a pointer to whom memory is not allocated. But the way he reacted, it was like I am wrong. Although I got the job but after that he said Mohit think about this question again. I don't know what he was trying to say. Please let me know is there any problem in my answer?

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  • Scanf fails with bus error

    - by Mikulas Dite
    I'm playing with C and I've run into this error: #include <stdio.h> int main () { char* foo; scanf("%s", foo); printf("entered %s", foo); return 0; } scanf takes pointer, foo is pointer, yet I get bus error. How can I make it work?

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  • Segmentation fault on writing char to char* address

    - by Lukas Dojcak
    hi guys, i've got problem with my little C program. Maybe you could help me. char* shiftujVzorku(char* text, char* pattern, int offset){ char* pom = text; int size = 0; int index = 0; while(*(text + size) != '\0'){ size++; } while(*(pom + index) != '\0'){ if(overVzorku(pom + index, pattern)){ while(*pattern != '\0'){ //vyment *pom s *pom + offset if(pom + index + offset < text + size){ char x = *(pom + index + offset); char y = *(pom + index); int adresa = *(pom + index + offset); *(pom + index + offset) = y; <<<<<< SEGMENTATION FAULT *(pom + index) = x; //*pom = *pom - *(pom + offset); //*(pom + offset) = *(pom + offset) + *pom; //*pom = *(pom + offset) - *pom; } else{ *pom = *pom - *(pom + offset - size); *(pom + offset - size) = *(pom + offset - size) + *pom; *pom = *(pom + offset - size) - *pom; } pattern++; } break; } index++; } return text; } Isn't important what's the programm doing. Mayby there's lot of bugs. But, why do I get SEGMENTATION FAULT (for destination see code) at this line? I'm, trying to write some char value to memory space, with help of address "pom + offset + index". Thanks for everything helpful. :)

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  • Is auto_ptr deprecated?

    - by idimba
    Is auto_ptr deprecated in incomming C++ standard? Is unique_ptr should be used for ownershipt transfer instead of share ptr? If unique_ptr is not in standard, than do I need use shared_ptr instead?

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  • Pointer initialization

    - by SoulBeaver
    Sorry if this question has been asked before. On my search through SO I didn't find one that asked what I wanted to know. Basically, when I have this: typedef struct node { int data; node *node; } *head; and do node *newItem = new node; I am under the impression that I am declaring and reserving space, but not defining, a pointer to struct node, is that correct? So when I do newItem->data = 100 and newItem->next = 0 I get confused. newItem = 0would declare what exactly? Both data and next? The object as a whole? I'm especially confused when I use typedef. Which part is the macro? I assume node because that's how I call it, but why do I need it? Finally, what happens when I do: node *temp; temp = new node; temp = head->next; head->next = newItem; newItem->next = temp; I mean, head-next is a pointer pointing to object newItem, so I assume not to newItem.data or next themselves. So how can I use an uninitialized pointer that I described above safely like here? is head now not pointing to an uninitialized pointer?

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  • How can I free all allocated memory at once?

    - by Tommy
    Here is what I am working with: char* qdat[][NUMTBLCOLS]; char** tdat[]; char* ptr_web_data; // Loop thru each table row of the query result set for(row_index = 0; row_index < number_rows; row_index++) { // Loop thru each column of the query result set and extract the data for(col_index = 0; col_index < number_cols; col_index++) { ptr_web_data = (char*) malloc((strlen(Data) + 1) * sizeof(char)); memcpy (ptr_web_data, column_text, strlen(column_text) + 1); qdat[row_index][web_data_index] = ptr_web_data; } } tdat[row_index] = qdat[col_index]; After the data is used, the memory allocated is released one at a time using free(). for(row_index = 0; row_index < number_rows; row_index++) { // Loop thru all columns used for(col_index = 0; col_index < SARWEBTBLCOLS; col_index++) { // Free memory block pointed to by results set array free(tdat[row_index][col_index]); } } Is there a way to release all the allocated memory at once, for this array? Thank You.

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  • Get Function Pointer to function in a shared library I didn't directly load

    - by bdk
    My Linux application (A) links against a Third Party shared Library (B) which I don't have source code to. This library makes use of another third party shared library that I don't have source code to (C). I believe that (B) uses dlopen to access (C) instead of directly linking. My reasoning for this is that 'ldd' on (B) does not show (C) and objdump -X (B) shows references to dlopen/dlclose/dlsym. My requirement is that I need to in my code for (A) get a function pointer to a function foo() located in (C). Normally I'd use dlsym for this, but I need to pass it the handle returned from dlopen which I don't have since (B) does not expose this. - For the larger context: I need to modify the function in (C) such that everytime it calls its helper function bar() (also located in (C)), it also calls a function with the same signature located in (A) with the same parameters (Basically inject my code into the codepath of (C) foo()-bar(). I believe I've found a way to accomplish this using gdb, but in order to port my gdb command list, but I'm stuck on the step of getting the function pointer. I'm also open to alternatives to accomplish the same task rather than the exact problem as stated above Edit: After writing this I realized I can probably just do another dlopen on the file in my code and the symbols returned via dlsym on that handle should be the same as received via the original dlopen, If I'm reading the dlopen man page correctly. However I'm still interested in advice or assistance with the my larger context, If theres a better way to go about this

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