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  • How to properly assign a value to the member of a struct that has a class data type?

    - by sasayins
    Hi, Please kindly see below for the codes. Its compiling successfully but the expected result is not working. Im very confused because my initialization of the array is valid, //cbar.h class CBar { public: class CFoo { public: CFoo( int v ) : m_val = v {} int GetVal() { return m_val; } private: int m_val; }; public: static const CFoo foo1; static const CFoo foo2; public: CBar( CFoo foo ) m_barval( foo.GetVal() ){} int GetFooVal() { return m_barval; } private: int m_barval; }; //cbar.cpp const CBar::CFoo foo1 = CBar::CFoo(2); const CBar::CFoo foo2 = CBar::CFoo(3); //main.cpp struct St { CBar::CFoo foo; }; St st[] = { CBar::foo1, CBar::foo2 }; for( int i=0; i<sizeof(st)/sizeof(St); i++ ) { CBar cbar( st[i].foo ); std::cout << cbar.GetFooVal() << std::endl; } But then when I change the St::foo to a pointer. And like assign the address of CBar::foo1 or CBar::foo2, its working, like this, //main.cpp struct St { const CBar::CFoo *foo; }; St st[] = { &CBar::foo1, &CBar::foo2 }; for( int i=0; i<sizeof(st)/sizeof(St); i++ ) { CBar cbar( *st[i].foo ); std::cout << cbar.GetFooVal() << std::endl; } The real problem is. The app should output 2 3 Please advice. Many thanks.

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  • Decayed multidimensional array return from function

    - by paul simmons
    related to http://stackoverflow.com/questions/2520535/gcc-multi-dim-array-or-double-pointer-for-warning-free-compile , is there a way to return so-called "decayed array pointer" from a function? in summary (suppose 2 dim array) returning int (*a)[5] format rather than int** format? as far as I see, when returned int** pointer is sent to another function waiting (int*)[] parameter, it is not working correctly.

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  • Useless variable name in C struct type definition

    - by user1210233
    I'm implementing a linked list in C. Here's a struct that I made, which represents the linked list: typedef struct llist { struct lnode* head; /* Head pointer either points to a node with data or NULL */ struct lnode* tail; /* Tail pointer either points to a node with data or NULL */ unsigned int size; /* Size of the linked list */ } list; Isn't the "llist" basically useless. When a client uses this library and makes a new linked list, he would have the following declaration: list myList; So typing llist just before the opening brace is practically useless, right? The following code basically does the same job: typedef struct { struct lnode* head; /* Head pointer either points to a node with data or NULL */ struct lnode* tail; /* Tail pointer either points to a node with data or NULL */ unsigned int size; /* Size of the linked list */ } list;

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  • Could I ever want to access the address zero?

    - by Joel
    The constant 0 is used as the null pointer in C and C++. But as in http://stackoverflow.com/questions/2389251/pointer-to-a-specific-fixed-address there seems to be some possible use of assigning fixed addresses. Is there ever any conceivable need, in any system, for whatever low level task, for accessing the address 0? If there is, how is that solved with 0 being the null pointer and all? If not, what makes it certain that there is not such a need?

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  • C++ new memory allocation fragmentation

    - by tamulj
    I was trying to look at the behavior of the new allocator and why it doesn't place data contiguously. My code: struct ci { char c; int i; } template <typename T> void memTest() { T * pLast = new T(); for(int i = 0; i < 20; ++i) { T * pNew = new T(); cout << (pNew - pLast) << " "; pLast = pNew; } } So I ran this with char, int, ci. Most allocations were a fixed length from the last, sometimes there were odd jumps from one available block to another. sizeof(char) : 1 Average Jump: 64 bytes sizeof(int): 4 Average Jump: 16 sizeof(ci): 8 (int has to be placed on a 4 byte align) Average Jump: 9 Can anyone explain why the allocator is fragmenting memory like this? Also why is the jump for char so much larger then ints and a structure that contains both an int and char.

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  • Returning and printing string array index in C

    - by user1781966
    I've got a function that searches through a list of names and I'm trying to get the search function to return the index of the array back to the main function and print out the starting location of the name found. Everything I've tried up to this point either crashes the program or results in strange output. Here is my search function: #include<stdio.h> #include<conio.h> #include<string.h> #define MAX_NAMELENGTH 10 #define MAX_NAMES 5 void initialize(char names[MAX_NAMES][MAX_NAMELENGTH], int Number_entrys, int i); int search(char names[MAX_NAMES][MAX_NAMELENGTH], int Number_entrys); int main() { char names[MAX_NAMES][MAX_NAMELENGTH]; int i, Number_entrys,search_result,x; printf("How many names would you like to enter to the list?\n"); scanf("%d",&Number_entrys); initialize(names,Number_entrys,i); search_result= search(names,Number_entrys); if (search_result==-1){ printf("Found no names.\n"); }else { printf("%s",search_result); } getch(); return 0; } void initialize(char names[MAX_NAMES][MAX_NAMELENGTH],int Number_entrys,int i) { if(Number_entrys>MAX_NAMES){ printf("Please choose a smaller entry\n"); }else{ for (i=0; i<Number_entrys;i++){ scanf("%s",names[i]); } } } int search(char names[MAX_NAMES][MAX_NAMELENGTH],int Number_entrys) { int x; char new_name[MAX_NAMELENGTH]; printf("Now enter a name in which you would like to search the list for\n"); scanf("%s",new_name); for(x = 0; x < Number_entrys; x++) { if ( strcmp( new_name, names[x] ) == 0 ) { return x; } } return -1; } Like I mentioned before I have tried a lot of different ways to try and fix this issue, but I cant seem to get them to work. Printing X like what I have above is just the last thing I tried, and therefor know that it doesn't work. Any suggestions on the simplest way to do this?

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  • C++ macro definition unclear

    - by Tony
    Is this a macro defintion for a class or what exactly is it? #define EXCEPTIONCLASS_IMPLEMENTATION(name, base, string) : public base \ { \ public: \ name() : base(string) {} \ name(const x::wrap_exc& next) : base(string,next) {}; \ name(const x::wrap_exc& prev, const x::wrap_exc& next) : \ base(prev, next) {}; \ }

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  • Big O Complexity of a method

    - by timeNomad
    I have this method: public static int what(String str, char start, char end) { int count=0; for(int i=0;i<str.length(); i++) { if(str.charAt(i) == start) { for(int j=i+1;j<str.length(); j++) { if(str.charAt(j) == end) count++; } } } return count; } What I need to find is: 1) What is it doing? Answer: counting the total number of end occurrences after EACH (or is it? Not specified in the assignment, point 3 depends on this) start. 2) What is its complexity? Answer: the first loops iterates over the string completely, so it's at least O(n), the second loop executes only if start char is found and even then partially (index at which start was found + 1). Although, big O is all about worst case no? So in the worst case, start is the 1st char & the inner iteration iterates over the string n-1 times, the -1 is a constant so it's n. But, the inner loop won't be executed every outer iteration pass, statistically, but since big O is about worst case, is it correct to say the complexity of it is O(n^2)? Ignoring any constants and the fact that in 99.99% of times the inner loop won't execute every outer loop pass. 3) Rewrite it so that complexity is lower. What I'm not sure of is whether start occurs at most once or more, if once at most, then method can be rewritten using one loop (having a flag indicating whether start has been encountered and from there on incrementing count at each end occurrence), yielding a complexity of O(n). In case though, that start can appear multiple times, which most likely it is, because assignment is of a Java course and I don't think they would make such ambiguity. Solving, in this case, is not possible using one loop... WAIT! Yes it is..! Just have a variable, say, inc to be incremented each time start is encountered & used to increment count each time end is encountered after the 1st start was found: inc = 0, count = 0 if (current char == start) inc++ if (inc > 0 && current char == end) count += inc This would also yield a complexity of O(n)? Because there is only 1 loop. Yes I realize I wrote a lot hehe, but what I also realized is that I understand a lot better by forming my thoughts into words...

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  • Buffer size: N*sizeof(type) or sizeof(var)? C++

    - by flyout
    I am just starting with cpp and I've been following different examples to learn from them, and I see that buffer size is set in different ways, for example: char buffer[255]; StringCchPrintf(buffer, sizeof(buffer), TEXT("%s"), X); VS char buffer[255]; StringCchPrintf(buffer, 255*sizeof(char), TEXT("%s"), X); Which one is the correct way to use it? I've seen this in other functions like InternetReadFile, ZeroMemory and MultiByteToWideChar.

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  • Why is this undefined behaviour?

    - by xryl669
    Here's the sample code: X * makeX(int index) { return new X(index); } struct Tmp { mutable int count; Tmp() : count(0) {} const X ** getX() const { static const X* x[] = { makeX(count++), makeX(count++) }; return x; } }; This reports Undefined Behaviour on CLang version 500 in the static array construction. For sake of simplication for this post, the count is not static, but it does not change anything.

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  • Rotate a linked list

    - by user408041
    I want to rotate a linked list that contains a number. 123 should be rotated to 231. The function created 23 but the last character stays empty, why? typedef struct node node; struct node{ char digit; node* p; }; void rotate(node** head){ node* walk= (*head); node* prev= (*head); char temp= walk->digit; while(walk->p!=NULL){ walk->digit=walk->p->digit; walk= walk->p; } walk->digit=temp; } How I create the list: node* convert_to_list(int num){ node * curr, * head; int i=0,length=0; char *arr=NULL; head = NULL; length =(int) log10(((double) num))+1; arr =(char*) malloc((length)*sizeof(char)); //allocate memory sprintf (arr, "%d" ,num); //(num, buf, 10); for(i=length;i>=0;i--) { curr = (node *)malloc(sizeof(node)); (curr)->digit = arr[i]; (curr)->p = head; head = curr; } curr = head; return curr; }

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  • typedef fixed length array

    - by Rajorshi
    Hi, I have to define a 24-bit data type.I am using char[3] to represent the type. Can I typedef char[3] to type24? I tried it in a code sample. I put typedef char[3] type42; in my header file. The compiler did not complain about it. But when I defined a function void foo(type24 val) {} in my C file, it did complain. I would like to be able to define functions like type24_to_int32(type24 val) instead of type24_to_int32(char value[3]).

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  • C++ static virtual members?

    - by cvb
    Is it possible in C++ to have a member function that is both static and virtual? Apperantly, there isn't a straight-forward way to do it (static virtual member(); is a complie error), but at least a way to acheive the same effect? I.E: struct Object { struct TypeInformation; static virtual const TypeInformation &GetTypeInformation() const; }; struct SomeObject : public Object { static virtual const TypeInformation &GetTypeInformation() const; }; It makes sence to use GetTypeInformation() both on an instance (object->GetTypeInformation()) and on a class (SomeObject::GetTypeInformation()), which can be useful for comparsions and vital for templates. The only ways I can think of involves writing two functions / a function and a constant, per class, or use macros. Any other solutions?

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  • Runtime error on Did End On Exit in iPhone application

    - by Deepak Pillai
    Does anyone know why im getting runtime error when i click on return button on iphone keyboard. I need to hide keyboard after done editing values to UITextField. So i assigned Did End On Exit to IBAction and the IBAction code below -(IBAction)FinishEditing:(id)sender { [folderName resignFirstResponder]; } When running ma project i facing a runtime error and the variable values shown below argv char ** 0xbffff58c *argv char * 0xbffff6b8 **argv char '/' Console Value (lldb) Any idea to overcome this issue??

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  • question about in -place sort

    - by davit-datuashvili
    for example we have following array char data[]=new char[]{'A','S','O','R','T','I','N','G','E','X','A','M','P','L','E'}; and index array int a[]=new int[]{0,1,2,3,4,5,6,7,8,9,10,11,12,13,14}: void insitu(char data[],int a[],N){ for (int i=0;i<N;i++) { char v=data[i]; int j,int k; for (k=i;a[k]!=i;k=a[j];a[j]=j) { j=k;data[k]=data[a[k]; } data[k]=v; a[k]=k; } i have question what is initialize value of j? when i run this code it asks me to initialize j and what should do? }

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  • sending address of a variable declared on the stack?

    - by kobac
    I have a doubt concerning declaring variables, their scope, and if their address could be sent to other functions even if they are declared on the stack? class A{ AA a; void f1(){ B b; aa.f2(&b); } }; class AA{ B* mb; f2(B* b){ mb = b; //... } }; Afterwards, I use my AA::mb pointer in the code. So things I would like to know are following. When the program exits A::f1() function, b variable since declared as a local variable and placed on the stack, can't be used anymore afterwards. What happens with the validity of the AA::mb pointer? It contains the address of the local variable which could not be available anymore, so the pointer isn't valid anymore? If B class is a std::<vector>, and AA::mb is not a pointer anymore to that vector, but a vector collection itself for example. I would like to avoid copying all of it's contents in AA::f2() to a member AA::mb in line mb = b. Which solution would you recommend since I can't assign a pointer to it, because it'll be destroyed when the program exits AA::f2()

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  • Incompatible format types

    - by nebffa
    I'm playing around with strncpy in C and am having some trouble. The code is as follows: #include <stdio.h> #include <string.h> int main(int argc, char *argv[]) { char src[] = "Benjamin Franklin"; char dest[5]; strncpy(src, dest, sizeof(dest) / sizeof(char)); dest[5] = '\0'; printf("%s\n", dest); return 0; } which compiles with no errors using: gcc -Wall -g -Werror test.c -o test and prints out gibberish like p4?? I cannot really understand what I'm doing wrong especially since I have played around with it a lot and been looking online for answers. Perhaps since I am using arrays I am passing the address to printf without realising it?

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  • Why does this program segfault

    - by Leda
    Upon compiling and running this small program to reverse a string, I get a Segmentation Fault before any output occurs. Forgive me if this is an obvious question, I'm still very new to C. #include <stdio.h> int reverse(char string[], int length); int main() { char string[] = "reversed"; printf("String at start of main = %s", string); reverse(string, sizeof(string)); printf("%s\n", string); return 0; } // Reverse string int reverse(char string[], int length) { int i; char reversed[] = {}; int temp; for(i = 0; i < length; ++i) { temp = string[i]; reversed[length - i] = temp; } return 0; }

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  • Is allocating a dynamic array without specifying size well formed code?

    - by Als
    The following simple program snippet gives compilation errorswith gcc-4.3.4. Program: int main() { char *ptr = new char[10]; char *ptr1 = new char[]; return 0; } Compilation errors: prog.cpp: In function ‘int main()’: prog.cpp:4: error: expected primary-expression before ‘]’ token prog.cpp:3: warning: unused variable ‘ptr’ prog.cpp:4: warning: unused variable ‘ptr1’ But the same compiles cleanly with MSVC without any diagnostic message. So my question is: Does the Standard allow an new [] to be called without specifying the size? Or this a bug in MSVC? Can someone provide a reference from the standard which will conclusively say that the above code example is ill-formed or well-formed? I have had a look at: 5.3.4 New [expr.new] & 18.4.1.2 Array forms [lib.new.delete.array] but couldnt find any conclusive evidence about the behavior.

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  • What is wrong with this append func in C

    - by LuckySlevin
    My Struct Definitions. typedef struct inner_list {char word[100]; inner_list*next;} inner_list; typedef struct outer_list { char word [100]; inner_list * head; outer_list * next; } outer_list; And The problem part: void append(outer_list **q,char num[100],inner_list *p) { outer_list *temp,*r; temp = *q; char *str; if(*q==NULL) { temp = (outer_list *)malloc(sizeof(outer_list)); strcpy(temp->word,num); temp->head = p; temp->next=NULL; *q=temp; } else { temp = *q; while(temp->next !=NULL) { temp=temp->next; } r = (outer_list *)malloc(sizeof(outer_list)); strcpy(r->word,num); temp->head = p; r->next=NULL; temp->next=r; } } I don't know what is i'm doing wrong in this append function i'm sending a char array and a linked list to be stored another linked list. But i can't store the linked list in another linked list. I couldn't figure out the problem. Any ideas?

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  • How to align C++ class member names in one column in emacs ?

    - by KotBerbelot
    I would like to align all C++ class member names ( do not confuse with member types ) in one column. Lets look at the example of what we have at entrance: class Foo { public: void method1( ); int method2( ); const Bar * method3( ) const; protected: float m_member; }; and this is what we would like to have at the end: class Foo { public: void method1( ); int method2( ); const Bar * method3( ) const; protected: float m_member; }; So the longest member type declaration defines the column to which class member names will be aligned. How can i perform such transformation in emacs ?

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  • JS and Jquery problem

    - by Sonny
    hi i got the problem the script.js gives me <div id="gracze"> <div id="10" class="char" style="z-index: 19; top: 592px; left: 608px; "></div> <div id="14" class="char" style="z-index: 25; top: 784px; left: 608px; "></div> </div> instead <div id="gracze"> <div id="4" class="char" ... ></div> <div id="10" class="char" style="z-index: 19; top: 592px; left: 608px; "></div> <div id="14" class="char" style="z-index: 25; top: 784px; left: 608px; "></div> </div> get_players.php 4/62/6 10/19/19 14/19/25 script.js function get_players() { $.ajax({ type: "POST", url: "get_players.php", dataType: "html", success: function(data) { var str = data; var chars = str.split("<br />"); var lol = chars.length; for(var i = lol; i--; ) { chars[i] = chars[i].split('/'); var o = document.getElementById(chars[i][0]); var aimt = i; if (!o) { if (aimt!=chars.length-1 && aimt != 0) { $('#gracze').html('<div id="'+chars[aimt][0]+'" class="char"></div>'+$('#gracze').html()); $('#'+chars[aimt][0]).css("top", chars[aimt][2]*32-16+"px"); $('#'+chars[aimt][0]).css("left", chars[aimt][1]*32+"px"); $('#'+chars[aimt][0]).css("z-index", chars[aimt][1]*32); } } else { $('#'+chars[aimt][0]).animate({ "top": chars[aimt][2]*32-16+"px", "left": chars[aimt][1]*32+"px" }, { duration: 275}); //$('#'+chars[aimt][0]).css("top", chars[aimt][1]*32-16+"px"); //$('#'+chars[aimt][0]).css("left", chars[aimt][2]*32+"px"); $('#'+chars[aimt][0]).css("z-index", chars[aimt][2]); } } }}); setTimeout("get_players();", 1000); } I think it's because of for(var i = lol; i--; ) {

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  • problems with 'free' in C

    - by lego69
    hello, can somebody please explain can I free const char* ? I allocated new memory using malloc and when I'm trying to free it I always receive an error incompatible pointer type thanks in advance something like this char* name="Arnold"; const char* str=malloc(stlen(name)+1); free(str); <- here bug

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  • Maximize/Minimize is causing Close Button to be re-enabled after disabling it -- Why?

    - by Brainsick
    I have used P/Invoke to call GetSystemMenu and EnableMenuItem (win32api) to disable the close functionality. However, after minimizing or maximizing my Windows Forms application the button is re-enabled. Obviously minimizing or maximizing is causing the behavior, but how? I'm not sure where to look to prevent this behavior. Should I be preventing the maximize and minimize behavior or is there something particularly wrong with the way in which I P/Invoked the calls? Once the application (main form) has loaded, I call the static method from a button click. class PInvoke { // P/Invoke signatures [DllImport("user32.dll")] static extern IntPtr GetSystemMenu(IntPtr hWnd, bool bRevert); [DllImport("user32.dll")] static extern bool EnableMenuItem(IntPtr hMenu, uint uIDEnableItem, uint uEnable); // SysCommand (WM_SYSCOMMAND) constant internal const UInt32 SC_CLOSE = 0xF060; // Constants used with Add/Check/EnableMenuItem internal const UInt32 MF_BYCOMMAND = 0x00000000; internal const UInt32 MF_ENABLED = 0x00000000; internal const UInt32 MF_GRAYED = 0x00000001; internal const UInt32 MF_DISABLED = 0x00000002; /// <summary> /// Sets the state of the Close (X) button and the System Menu close functionality. /// </summary> /// <param name="window">Window or Form</param> /// <param name="bEnabled">Enabled state</param> public static void EnableCloseButton(IWin32Window window, bool bEnabled) { IntPtr hSystemMenu = GetSystemMenu(window.Handle, false); EnableMenuItem(hSystemMenu, SC_CLOSE, MF_BYCOMMAND | (bEnabled ? MF_ENABLED : MF_GRAYED)); } }

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