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  • Question about Virtual Inheritance hierarchy

    - by Summer_More_More_Tea
    Hi there: I encounter this problem when tackling with virtual inheritance. I remember that in a non-virtual inheritance hierarchy, object of sub-class hold an object of its direct super-class. What about virtual inheritance? In this situation, does object of sub-class hold an object of its super-class directly or just hold a pointer pointing to an object of its super-class? By the way, why the output of the following code is: sizeof(A): 8 sizeof(B): 20 sizeof(C): 20 sizeof(C): 36 Code: #include <iostream> using namespace std; class A{ char k[ 3 ]; public: virtual void a(){}; }; class B : public virtual A{ char j[ 3 ]; public: virtual void b(){}; }; class C : public virtual B{ char i[ 3 ]; public: virtual void c(){}; }; class D : public B, public C{ char h[ 3 ]; public: virtual void d(){}; }; int main( int argc, char *argv[] ){ cout << "sizeof(A): " << sizeof( A ) << endl; cout << "sizeof(B): " << sizeof( B ) << endl; cout << "sizeof(C): " << sizeof( C ) << endl; cout << "sizeof(D): " << sizeof( D ) << endl; return 0; } Thanks in advance. Kind regards.

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  • Can some tell me why I am seg faulting in this simple C program?

    - by user299648
    I keep on getting seg faulted after I end my first for loop, and for the life of me I don't why. The file I'm scanning is just 18 strings in 18 lines. I thinks the problem is the way I'm mallocing the double pointer called picks, but I don't know exactly why. I'm am only trying to scanf strings that are less than 15 chars long, so I don't see the problem. Can someone please help. #include <stdio.h> #include <stdlib.h> #include <string.h> #define MAX_LENGTH 100 int main( int argc,char *argv[] ) { char* string = malloc( 15*sizeof(char) ); char** picks = malloc(15*sizeof(char*)); FILE* pick_file = fopen( argv[l], "r" ); int num_picks; for( num_picks=0 ; fgets( string, MAX_LENGTH, pick_file ) != NULL ; num_picks++ ) { scanf( "%s", picks+num_picks ); } //this is where i seg fault int x; for(x=0; x<num_picks;x++) printf("s\n", picks+x); }

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  • C++ - what does the colon after a constructor mean?

    - by waitinforatrain
    I'd happily Google this but don't know what to call it to Google it. I have a piece of code here: class demo { private: unsigned char len, *dat; public: demo(unsigned char le = 5, unsigned char default) : len(le) { dat = new char[len]; for (int i = 0; i <= le; i++) dat[i] = default; } void ~demo(void) { delete [] *dat; } }; class newdemo : public demo { private: int *dat1; public: newdemo(void) : demo(0, 0) { *dat1 = 0; return 0; } }; (It's from a past exam paper and the question is to correct errors in the code so ignore errors!) My question is, what are the ": len(le) " and " : demo(0, 0)" called? Something to do with inheritance?

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  • What's pcap_pkthdr there for?

    - by httpinterpret
    Code snippet from here: void packet_handler(u_char *param, const struct pcap_pkthdr *header, const u_char *pkt_data) { .... /* retireve the position of the ip header */ ih = (ip_header *) (pkt_data + 14); //length of ethernet header .... What's const struct pcap_pkthdr *header for, when do we need it, how is it populated (since there is no such info in the packet itself as below)?

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  • C++ Class Access Specifier Verbosity

    - by PolyTex
    A "traditional" C++ class (just some random declarations) might resemble the following: class Foo { public: Foo(); explicit Foo(const std::string&); ~Foo(); enum FooState { Idle, Busy, Unknown }; FooState GetState() const; bool GetBar() const; void SetBaz(int); private: struct FooPartialImpl; void HelperFunction1(); void HelperFunction2(); void HelperFunction3(); FooPartialImpl* m_impl; // smart ptr FooState m_state; bool m_bar; int m_baz; }; I always found this type of access level specification ugly and difficult to follow if the original programmer didn't organize his "access regions" neatly. Taking a look at the same snippet in a Java/C# style, we get: class Foo { public: Foo(); public: explicit Foo(const std::string&); public: ~Foo(); public: enum FooState { Idle, Busy, Unknown }; public: FooState GetState() const; public: bool GetBar() const; public: void SetBaz(int); private: struct FooPartialImpl; private: void HelperFunction1(); private: void HelperFunction2(); private: void HelperFunction3(); private: FooPartialImpl* m_impl; // smart ptr private: FooState m_state; private: bool m_bar; private: int m_baz; }; In my opinion, this is much easier to read in a header because the access specifier is right next to the target, and not a bunch of lines away. I found this especially true when working with header-only template code that wasn't separated into the usual "*.hpp/*.inl" pair. In that scenario, the size of the function implementations overpowered this small but important information. My question is simple and stems from the fact that I've never seen anyone else actively do this in their C++ code. Assuming that I don't have a "Class View" capable IDE, are there any obvious drawbacks to using this level of verbosity? Any other style recommendations are welcome!

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  • Potential problem with C standard malloc'ing chars.

    - by paxdiablo
    When answering a comment to another answer of mine here, I found what I think may be a hole in the C standard (c1x, I haven't checked the earlier ones and yes, I know it's incredibly unlikely that I alone among all the planet's inhabitants have found a bug in the standard). Information follows: Section 6.5.3.4 ("The sizeof operator") para 2 states "The sizeof operator yields the size (in bytes) of its operand". Para 3 of that section states: "When applied to an operand that has type char, unsigned char, or signed char, (or a qualified version thereof) the result is 1". Section 7.20.3.3 describes void *malloc(size_t sz) but all it says is "The malloc function allocates space for an object whose size is specified by size and whose value is indeterminate". It makes no mention at all what units are used for the argument. Annex E startes the 8 is the minimum value for CHAR_BIT so chars can be more than one byte in length. My question is simply this: In an environment where a char is 16 bits wide, will malloc(10 * sizeof(char)) allocate 10 chars (20 bytes) or 10 bytes? Point 1 above seems to indicate the former, point 2 indicates the latter. Anyone with more C-standard-fu than me have an answer for this?

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  • Struct Array Initialization and String Literals

    - by Christian Ammer
    Is following array initialization correct? I guess it is, but i'm not really sure if i can use const char* or if i better should use std::string. Beside the first question, do the char pointers point to memory segments of same sizes? struct qinfo { const char* name; int nr; }; qinfo queues[] = { {"QALARM", 1}, {"QTESTLONGNAME", 2}, {"QTEST2", 3}, {"QIEC", 4} };

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  • What's the C strategy to "imitate" a C++ template ?

    - by Andrei Ciobanu
    After reading some examples on stackoverflow, and following some of the answers for my previous questions (1), I've eventually come with a "strategy" for this. I've come to this: 1) Have a declare section in the .h file. Here I will define the data-structure, and the accesing interface. Eg.: /** * LIST DECLARATION. (DOUBLE LINKED LIST) */ #define NM_TEMPLATE_DECLARE_LIST(type) \ typedef struct nm_list_elem_##type##_s { \ type data; \ struct nm_list_elem_##type##_s *next; \ struct nm_list_elem_##type##_s *prev; \ } nm_list_elem_##type ; \ typedef struct nm_list_##type##_s { \ unsigned int size; \ nm_list_elem_##type *head; \ nm_list_elem_##type *tail; \ int (*cmp)(const type e1, const type e2); \ } nm_list_##type ; \ \ nm_list_##type *nm_list_new_##type##_(int (*cmp)(const type e1, \ const type e2)); \ \ (...other functions ...) 2) Wrap the functions in the interface inside MACROS: /** * LIST INTERFACE */ #define nm_list(type) \ nm_list_##type #define nm_list_elem(type) \ nm_list_elem_##type #define nm_list_new(type,cmp) \ nm_list_new_##type##_(cmp) #define nm_list_delete(type, list, dst) \ nm_list_delete_##type##_(list, dst) #define nm_list_ins_next(type,list, elem, data) \ nm_list_ins_next_##type##_(list, elem, data) (...others...) 3) Implement the functions: /** * LIST FUNCTION DEFINITIONS */ #define NM_TEMPLATE_DEFINE_LIST(type) \ nm_list_##type *nm_list_new_##type##_(int (*cmp)(const type e1, \ const type e2)) \ {\ nm_list_##type *list = NULL; \ list = nm_alloc(sizeof(*list)); \ list->size = 0; \ list->head = NULL; \ list->tail = NULL; \ list->cmp = cmp; \ }\ void nm_list_delete_##type##_(nm_list_##type *list, \ void (*destructor)(nm_list_elem_##type elem)) \ { \ type data; \ while(nm_list_size(list)){ \ data = nm_list_rem_##type(list, tail); \ if(destructor){ \ destructor(data); \ } \ } \ nm_free(list); \ } \ (...others...) In order to use those constructs, I have to create two files (let's call them templates.c and templates.h) . In templates.h I will have to NM_TEMPLATE_DECLARE_LIST(int), NM_TEMPLATE_DECLARE_LIST(double) , while in templates.c I will need to NM_TEMPLATE_DEFINE_LIST(int) , NM_TEMPLATE_DEFINE_LIST(double) , in order to have the code behind a list of ints, doubles and so on, generated. By following this strategy I will have to keep all my "template" declarations in two files, and in the same time, I will need to include templates.h whenever I need the data structures. It's a very "centralized" solution. Do you know other strategy in order to "imitate" (at some point) templates in C++ ? Do you know a way to improve this strategy, in order to keep things in more decentralized manner, so that I won't need the two files: templates.c and templates.h ?

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  • Can someone tell me why I'm seg faulting in this simple C program?

    - by user299648
    I keep on getting seg faulted, and for the life of me I dont why. The file I'm scanning is just 18 strings in 18 lines. I thinks the problem is the way I'm mallocing the double pointer called picks, but I dont know exactly why. I'm am only trying to scanf strings that are less than 15 chars long, so I don't see the problem. Can someone please help. #include <stdio.h> #include <stdlib.h> #include <string.h> #define MAX_LENGTH 100 int main( int argc,char *argv[] ) { char* string = malloc( sizeof(char) ); char** picks = malloc(15*sizeof(char)); FILE* pick_file = fopen( argv[l], "r" ); int num_picks; for( num_picks=0 ; fgets( string, MAX_LENGTH, pick_file ) != NULL ; num_picks++ ) { printf("pick a/an %s ", string ); scanf( "%s", picks+num_picks ); } int x; for(x=0; x<num_picks;x++) printf("s\n", picks+x); }

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  • How to fill two-dimensional array using java enhanced loop?

    - by Shark
    Basically, I am trying this, but this only leaves array filled with zeros. I know how to fill it with normal for loop (such as for (int i = 0; i < array.length; i++) and so on), but why is my variant is not working? Any help would be appreciated. char[][] array = new char[x][y]; for (char[] row : array) for (char element : row) element = '~';

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  • Argc/Argv C Problems

    - by Salman
    Hey all, If I have the following code: main(int argc, char *argv[]){ char serveradd[20]; strcpy(serveradd, argv[1]); int port = atoi(argv[2]); printf("%s %d \n", serveradd, port); The first two arguments to the command line are printed. However, if I do this: char serveradd[20]; strcpy(serveradd, argv[1]); int port = atoi(argv[2]); char versionnum[1]; strcpy(versionnum, argv[3]); printf("%s %d %s \n", serveradd, port, versionnum);` The first argument (serveradd) does not print out to the screen and is not being stored... Why is this happening and how can I fix it? Thanks!

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  • Silencing GCC warnings when using an "Uncopyable" class

    - by Kazade
    I have several classes that I don't want to be copyable, some of these classes have pointer data members. To make these classes uncopyable I privately inherit the following class template: template <class T> class Uncopyable { protected: Uncopyable() {} virtual ~Uncopyable() {} private: Uncopyable(const Uncopyable &); T & operator=(const T&); }; Which I used like so: class Entity : private Uncopyable<Entity> { } This works fine, however when I compile with -Weffc++ I still get the following warning: class Entity has pointer data members but does not override Entity(const Entity&) or operator=(const Entity&) Why is it still giving me this warning?

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  • How do the operators < and > work with pointers?

    - by Øystein
    Just for fun, I had a std::list of const char*, each element pointing to a null-terminated text string, and ran a std::list::sort() on it. As it happens, it sort of (no pun intended) did not sort the strings. Considering that it was working on pointers, that makes sense. According to the documentation of std::list::sort(), it (by default) uses the operator < between the elements to compare. Forgetting about the list for a moment, my actual question is: How do these (, <, =, <=) operators work on pointers in C++ and C? Do they simply compare the actual memory addresses? char* p1 = (char*) 0xDAB0BC47; char* p2 = (char*) 0xBABEC475; e.g. on a 32-bit, little-endian system, p1 p2 because 0xDAB0BC47 0xBABEC475? Testing seems to confirm this, but I thought it'd be good to put it on StackOverflow for future reference. C and C++ both do some weird things to pointers, so you never really know...

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  • Make: how make all hidden files in the current makefile?

    - by HH
    It traverses to bottom dirs for some unknown reason: Errorsome /bin/sh: .??*: not found make[23]: Entering directory `/m/user/files/dir' make clean Makefile all: make clean #The wildcard is the bug. I want to make all hidden files in the current makefile. #It should match .<some char><some char><any char arbitrary times> make $$(.??*) #I want to replace below-like-tihngs with a wildcard above # make .lambda # make .lambda_t clean: -rm .??* .lambda: #do something .lambda_t:

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  • C++ multiple definition error

    - by user231536
    Starting with sth's answer to this question: http://stackoverflow.com/questions/3023760/c-template-specialization I was wondering how to resolve multiple definition errors if the following code is put in a header file included multiple times by different .cc files and linked together: template <typename T> class C { static const int K; static ostream& print(ostream& os, const T& t) { return os << t;} }; // general case template <typename T> const int C<T>::K = 1; // specialization template <> const int C<int>::K = 2;

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  • oracle collection not enough values

    - by john
    I did following: create or replace type my_row as object ( lname varchar2(30), fname varchar2(30), MI char(1), hohSSN char (9), hohname VARCHAR2(63), hohDob char(10), dob DATE ); create or replace type eiv.my_rec as table of eiv.my_row; but then doing query like: my_records my_rec select '', '', '', '', '', '', sysdate bulk collect into my_records from dual; gives error ORA-00947: not enough values what can i be doing wrong here?

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  • Why is my implementation of strcmp not returning the proper value?

    - by Avanish Giri
    Why is this printing out 0 back in main but 6 when it is inside of the strcmp function? 7 int main() 8 { 9 char* str = "test string"; 10 char* str2 = "test strong"; 11 //printf("string length = %d\n",strlen(str)); 12 13 int num = strcmp(str,str2); 14 15 printf("num = %d\n",num); 16 } 29 int strcmp(char* str, char* str2) 30 { 31 if(*str == '\0' && *str2 == '\0') 32 return 0; 33 if(*str2 - *str == 0) 34 { 35 strcmp(str+1,str2+1); 36 } 37 else 38 { 39 int num = *str2 - *str; 40 cout << "num = " <<num<<endl; 41 return num; 42 } 43 } The output is: num = 6 num = 0 Why is it printing 0 when obviously the value that it should be returning is 6?

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  • Gtk, whether destroying GtkBuilder destroies all the screens and widgets?

    - by PP
    Hi, Question regarding GtkBuilder. When we unref builder pointer does it destroys all the screens/widgets the builder had created? if( builder_ptr ) g_object_unref(G_OBJECT(builder_ptr)); Suppose we have created one screen using Glade/XML with some 2-3 top_level windows in it gtk_builder_add_from_file(builder_ptr, "Test.glade", &error ) and generated GtkBuilder pointer (as above) so after deleting this pointer does it deletes created Windows or do we need to manually delete these windows? Thanks, PP.

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  • boost::enable_if class template method

    - by aaa
    I got class with template methods that looks at this: struct undefined {}; template<typename T> struct is_undefined : mpl::false_ {}; template<> struct is_undefined<undefined> : mpl::true_ {}; template<class C> struct foo { template<class F, class V> typename boost::disable_if<is_undefined<C> >::type apply(const F &f, const V &variables) { } template<class F, class V> typename boost::enable_if<is_undefined<C> >::type apply(const F &f, const V &variables) { } }; apparently, both templates are instantiated, resulting in compile time error. is instantiation of template methods different from instantiation of free functions? I have fixed this differently, but I would like to know what is up. Thank you

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  • Linked lists in Java - help with assignment

    - by user368241
    Representation of a string in linked lists In every intersection in the list there will be 3 fields : The letter itself. The number of times it appears consecutively. A pointer to the next intersection in the list. The following class CharNode represents a intersection in the list : public class CharNode { private char _data; private int _value; private charNode _next; public CharNode (char c, int val, charNode n) { _data = c; _value = val; _next = n; } public charNode getNext() { return _next; } public void setNext (charNode node) { _next = node; } public int getValue() { return _value; } public void setValue (int v) { value = v; } public char getData() { return _data; } public void setData (char c) { _data = c; } } The class StringList represents the whole list : public class StringList { private charNode _head; public StringList() { _head = null; } public StringList (CharNode node) { _head = node; } } Add methods to the class StringList according to the details : (I will add methods gradually according to my specific questions) (Pay attention, these are methods from the class String and we want to fulfill them by the representation of a string by a list as explained above) public int indexOf (int ch) - returns the index in the string it is operated on of the first appeareance of the char "ch". If the char "ch" doesn't appear in the string, returns -1. If the value of fromIndex isn't in the range, returns -1. Pay attention to all the possible error cases. Write what is the time complexity and space complexity of every method that you wrote. Make sure the methods you wrote are effective. It is NOT allowed to use ready classes of Java. It is NOT allowed to move to string and use string operations. Here is my try to write the method indexOf (int ch). Kindly assist me with fixing the bugs so I can move on. public int indexOf (int ch) { int count = 0; charNode pose = _head; if (pose == null ) { return -1; } for (pose = _head; pose!=null && pose.getNext()!='ch'; pose = pose.getNext()) { count++; } if (pose!=null) return count; else return -1; }

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  • Wierdness debugging Visual Studio C++ 2008

    - by Jeff Dege
    I have a legacy C++ app, that in its most incarnation we've been building with makefiles and VS2003's command-line tool. I'm trying to get it to build using VS2008 and MsBuild. The build is working OK, but I'm getting errors where I'd never seen errors, before, and stepping through in VS2008's debugger only confuses me. The app links a number of static libraries, which fall into two categories: those that are part of the same application suite, and those that are shared between a number of application suites. Originally, I had a .csproj file for each static library, and two .sln files, one for the application suite (including the suite-specific libraries) and one for the non-suite-specific shared libraries. The shared libraries were included in the link, their projects were not included in the application suite .sln. The application instantiates an object from a class that is defined in one of the shared libraries. The class has a member object of a class that wraps a linked list. The constructor of the linked list class sets its "head" pointer to null. When I run the app, and try to add an element to the linked list, I get an error - the head pointer contains the value 0xCCCCCCCC. So I step through with the debugger. And see weirdness. When the current line in the debugger is in a source file belonging to the static library, the head pointer contains 0x00000000. When I step into the constructor, I can see the pointer being set to that value, and when I'm stepped into any other method of the class, I can see that the head pointer still contains 0x00000000. But when I step out into methods that are defined in the application suite .sln, it contains 0xCCCCCCCC. It's not like it's being overwritten. It changes back and forth depending upon which source file I am currently debugging. So I included the shared library's project in the application suite .sln, and now I see the head pointer containing 0xCCCCCCCC all the time. It looks like the constructor of the linked list class is not being called. So now, I'm entirely confused. Anyone have any ideas?

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  • Reading data from text file in C

    - by themake
    I have a text file which contains words separated by space. I want to take each word from the file and store it. So i have opened the file but am unsure how to assign the word to a char. FILE *fp; fp = fopen("file.txt", "r"); //then i want char one = the first word in the file char two = the second word in the file

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  • Truncating a string while storing it in an array in c

    - by Nick
    I am trying to create an array of 20 character strings with a maximum of 17 characters that are obtained from a file named "words.dat". After that the program should truncate the string only showing the first 17 characters and completely ignore the rest of that string. However My question is: I am not quite sure how to accomplish this, can anyone give me some insight on how to accomplish this task? Here is my current code as is: #include <stdio.h> #include <stdlib.h> #define WORDS 20 #define LENGTH 18 char function1(char[WORDS][LENGTH]); int main( void ) { char word_array [WORDS] [LENGTH]; function1(word_array); return ( 0 ) ; } char function1(char word_array[WORDS][LENGTH]) { FILE *wordsfile = fopen("words.dat", "r"); int i = 0; if (wordsfile == NULL) printf("\nwords.dat was not properly opened.\n"); else { for (i = 0; i < WORDS; i++) { fscanf(wordsfile, "%17s", word_array[i]); printf ("%s \n", word_array[i]); } fclose(wordsfile); } return (word_array[WORDS][LENGTH]); } words.dat file: Ninja DragonsFury failninja dragonsrage leagueoflegendssurfgthyjnu white black red green yellow green leagueoflegendssughjkuj dragonsfury Sword sodas tiger snakes Swords Snakes sage Sample output: blahblah@fang:~>a.out Ninja DragonsFury failninja dragonsrage leagueoflegendssu rfgthyjnu white black red green yellow green leagueoflegendssu ghjkuj dragonsfury Sword sodas tiger snakes Swords blahblah@fang:~> What will be accomplished afterwards with this program is: After function1 works properly I will then create a second function name "function2" that will look throughout the array for matching pairs of words that match "EXACTLY" including case . After I will create a third function that displays the 20 character strings from the words.dat file that I previously created and the matching words.

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