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• how does fgets internally works?

  - by Registered User

  Well it is a basic question but I seem confused enough. #include<stdio.h> int main() { char a[100]; printf("Enter a string\n"); scanf("%s",a); } Basically the above is what I want to achieve. If I enter a string James Bond then I want that to be stored in array a. But the problem is because of presence of a blank space in between only James word is stored. So how can I solve this one. UPDATE After the replies given below I understand fgets() would be a better choice. I want to know internal working of fgets as why is it able to store the string with space where as scanf is not able to do the same.

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• SDL_BlitSurface() not displaying image?

  - by Christian Gonzalez

  So I'm trying to display a simply image with the SDL library, but when I use the function SDL_BlitSurface() nothing happens, and all I get is a black screen. I should also note that I have the .bmp file, the source, and the executable file all in the same directory. //SDL Header #include "SDL/SDL.h" int main(int argc, char* args[]) { //Starts SDL SDL_Init(SDL_INIT_EVERYTHING); //SDL Surfaces are images that are going to be displayed. SDL_Surface* Hello = NULL; SDL_Surface* Screen = NULL; //Sets the size of the window (Length, Height, Color(bits), Sets the Surface in Software Memory) Screen = SDL_SetVideoMode(640, 480, 32, SDL_SWSURFACE); //Loads a .bmp image Hello = SDL_LoadBMP("Hello.bmp"); //Applies the loaded image to the screen SDL_BlitSurface(Hello, NULL, Screen, NULL); //Update Screen SDL_Flip(Screen); //Pause SDL_Delay(2000); //Deletes the loaded image from memory SDL_FreeSurface(Hello); //Quits SDL SDL_Quit(); return 0; }

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• charset problem?

  - by Ben Fransen

  Hi all, I have a bugging problem. For a website I made there are search engine friendly URL's generated. The only problem is there are ß-chars in the url too. Chars like ö, ï, ä, ü etc. are placed correct. But with the ß-char there is a diamond-icon with a questionmark in it. I thought it had to do with the charset which is used but i've tried both UTF-8 and iso-8859-1. Both without luck. I need to have the correct character in the url for the readability of deeplinks. Hope to hear from you!

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• C++: Everytime I read in by fstream I got 1 extra character at the end

  - by Harry Pham

  Everytime I read in by fstream I got 1 extra character at the end, How can I avoid this? EDIT: ifstream readfile(inputFile); ofstream writefile(outputFile); char c; while(!readfile.eof()){ readfile >> c; //c = shiftChar(c, RIGHT, shift); writefile << c; } readfile.close(); writefile.close();

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• Initialize a static member ( an array) in C++

  - by Jimmy zhang

  I intended to create a class which only have static members and static functions. One of the member variable is an array. Would it be possible to initialize it without using constructors? I am having lots of linking errors right now... Class A{ public: static char a[128]; static void do_something(); } How would you initialize a[128]? Why can't I initialize a[128] by directly specifying its value like in C? a[128={1,2,3,...};

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• process semaphores linux - wait

  - by coubeatczech

  Hi, I try to code a simple program that starts and waits on the system semaphore until it gets terminated by signal. union semun { int val; struct semid_ds *buf; unsigned short int *array; struct seminfo *__buf; }; int main(){ int semaphores = semget(IPC_PRIVATE,1,IPC_CREAT | 0666); union semun arg; arg.val = 0; semctl(semaphores,0,SETVAL,arg); struct sembuf operations[1]; operations[0].sem_num = 0; operations[0].sem_op = -1; operations[0].sem_flg = 0; semop(semaphores,operations,1); fprintf(stderr,"Why?\n"); return 0; } I expect, that everytime this program gets executed, nothing actually happens and it waits on the semaphore, but everytime it goes through the semaphore and writes Why?. Why?

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• QT4 Designer - Implement Widget

  - by MOnsDaR

  I'm currently trying to get into QT4 and figure out a workflow for myself. While trying to create a widget which allows the user to connect to a hostname:port some questions appeared. The widget itself contains a LineEdit for entering the hostname, a SpinBox for entering the port and a PushButton which should emit a connect(QString hostname, unsigned int port) signal. In QTDesigner I created the necessary Form. It is saved as a .ui-File. Now the big question is how could I implement the widget? Is there a place in QTDesigner where I could add my signal to the Widget? Where could I add custom Properties? I've learned in another tutorial, which showed how to create a Widget in C++, how signals, slots, Q_PROPERTIES etc are defined and added to the widget. But there is no sourcecode in QTDesigner. Another option would be to generate sourcecode using uic. But the header says, that another generate would overwrite any changes to the sourcefiles. So how can I create a QT-widget completely with my own signals, slots and properties by using the QTDesigner for creating the UI and not having to recode everything whenever the UI is changing. Is there some kind of Roundtrip-Engineering? If thats not possible: Whats the sense of creating a Widget with QTDesigner then?

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• const read only local copies

  - by robUK

  Hello gcc 4.4.4 c89 I am just wondering is it worth passing a const into a function. i.e. void do_something(const char *dest, const int size) The size is a read-only so I don't want to change it. However, some developers never have this as const has it is a local copy that is being used. The pointer is const as you can change the value in the calling routine. I always have a const on read-only local copies, as it confirms to anyone reading my code that it is a read-only variable. And also, when coding I don't make the mistake of changing it without realizing. Many thanks for any suggestions,

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• Writing a VM - well formed bytecode?

  - by David Titarenco

  Hi, I'm writing a virtual machine in C just for fun. Lame, I know, but luckily I'm on SO so hopefully no one will make fun :) I wrote a really quick'n'dirty VM that reads lines of (my own) ASM and does stuff. Right now, I only have 3 instructions: add, jmp, end. All is well and it's actually pretty cool being able to feed lines (doing it something like write_line(&prog[1], "jmp", regA, regB, 0); and then running the program: while (machine.code_pointer <= BOUNDS && DONE != true) { run_line(&prog[machine.cp]); } I'm using an opcode lookup table (which may not be efficient but it's elegant) in C and everything seems to be working OK. My question is more of a "best practices" question but I do think there's a correct answer to it. I'm making the VM able to read binary files (storing bytes in unsigned char[]) and execute bytecode. My question is: is it the VM's job to make sure the bytecode is well formed or is it just the compiler's job to make sure the binary file it spits out is well formed? I only ask this because what would happen if someone would edit a binary file and screw stuff up (delete arbitrary parts of it, etc). Clearly, the program would be buggy and probably not functional. Is this even the VM's problem? I'm sure that people much smarter than me have figured out solutions to these problems, I'm just curious what they are!

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• How can I ensure that a Java object (containing cryptographic material) is zeroized?

  - by Jeremy Powell

  My concern is that cryptographic keys and secrets that are managed by the garbage collector may be copied and moved around in memory without zeroization. As a possible solution, is it enough to: public class Key { private char[] key; // ... protected void finalize() throws Throwable { try { for(int k = 0; k < key.length; k++) { key[k] = '\0'; } } catch (Exception e) { //... } finally { super.finalize(); } } // ... }

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• Are memcached entries saved by the Danga client compatible with the Spy client?

  - by jigjig

  After saving a String value into memcached using the Danga client, I attempted to get the entry using the Spy client. The two String values are not the same. The Danga client retrieves a string with an additional empty char prepended to the string, therefore violating the equality condition. Danga: t,e,s,t,s,t,r,i,n,g Spy: ,t,e,s,t,s,t,r,i,n,g I also attempted to save a serialized Map using the Danga client and get the Map using the Spy client. The Spy client is able to only get a String form of the Map. The string contains binary values, as below: sr

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• va_arg with pointers

  - by Yktula

  I want to initialize a linked list with pointer arguments like so: /* * Initialize a linked list using variadic arguments * Returns the number of structures initialized */ int init_structures(struct structure *first, ...) { struct structure *s; unsigned int count = 0; va_list va; va_start(va, first); for (s = first; s != NULL; s = va_arg(va, (struct structure *))) { if ((s = malloc(sizeof(struct structure))) == NULL) { perror("malloc"); exit(EXIT_FAILURE); } count++; } va_end(va); return count; } The problem is that clang errors type name requires a specifier or qualifier at va_arg(va, (struct structure *)), and says that the type specifier defaults to int. It also notes instantiated form at (struct structure *) and struct structure *. This, what seems to be getting assigned to s is int (struct structure *). It compiles fine when parentheses are removed from (struct structure *), but the structures that are supposed to be initialized are inaccessible. Why is int assumed when parentheses are around the type argument passed to va_arg? How can I fix this?

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• Declaration, allocation and assignment of an array of pointers to function pointers

  - by manneorama

  Hello Stack Overflow! This is my first post, so please be gentle. I've been playing around with C from time to time in the past. Now I've gotten to the point where I've started a real project (a 2D graphics engine using SDL, but that's irrelevant for the question), to be able to say that I have some real C experience. Yesterday, while working on the event system, I ran into a problem which I couldn't solve. There's this typedef, //the void parameter is really an SDL_Event*. //but that is irrelevant for this question. typedef void (*event_callback)(void); which specifies the signature of a function to be called on engine events. I want to be able to support multiple event_callbacks, so an array of these callbacks would be an idea, but do not want to limit the amount of callbacks, so I need some sort of dynamic allocation. This is where the problem arose. My first attempt went like this: //initial size of callback vector static const int initial_vecsize = 32; //our event callback vector static event_callback* vec = 0; //size static unsigned int vecsize = 0; void register_event_callback(event_callback func) { if (!vec) __engine_allocate_vec(vec); vec[vecsize++] = func; //error here! } static void __engine_allocate_vec(engine_callback* vec) { vec = (engine_callback*) malloc(sizeof(engine_callback*) * initial_vecsize); } First of all, I have omitted some error checking as well as the code that reallocates the callback vector when the number of callbacks exceed the vector size. However, when I run this code, the program crashes as described in the code. I'm guessing segmentation fault but I can't be sure since no output is given. I'm also guessing that the error comes from a somewhat flawed understanding on how to declare and allocate an array of pointers to function pointers. Please Stack Overflow, guide me.

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• Unicode and PHP - am I doing something wrong?

  - by alex

  I'm using Kohana 3, which has full support for Unicode. I have this as the first child of my <head> <meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /> The Unicode character I am inserting into is é as in Café. However, I am getting the triangle with a ? (as in could not decode character). As far as I can tell in my own code, I am not doing any string manipulation on the text. In fact, I have placed the accent straight into a view's PHP file and it is still not working. I copied the character from this page: http://www.fileformat.info/info/unicode/char/00e9/index.htm I've only just started examining PHP's Unicode limitations, so I could be doing something horribly wrong. So, how do I display this character? Do I need to resort to the HTML entity?

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• Implement a Cellular Automaton ? "Rule 110"

  - by ZaZu

  I was wondering how to use the Rule 110, with 55 lines and 14 cells. I have to then display that in an LED matrix display. Anyway my question is, how can I implement such automaton ?? I dont really know where to start, can someone please shed some light on how can I approach this problem ? Is there a specific METHOD I must follow ? Thanks --PROGRAM USED IS - C EDIT char array[54][14]; for(v=0;v<55;v++){ for(b=0;b<15;b++){ if(org[v][b-1]==0 && org[v][b]==0 && org[v][b+1] == 0) { array[v][b]=0; } array[v][b]=org[v][b]; } } Does that make sense ?? org stands for original

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• return first non repeating character in a string

  - by Amm Sokun

  I had to solve this question in which given a string, i had to return the first non repeating character present in the string. I solved it using hashtable and wrote a method which takes a constant reference to the string and returns the first non repeating character. However, when there is no non repeating character present in the string, i return -1 and in the main program i check as follows char c = firstNonRepeating( word ); if (static_cast<int> (c) == -1) cout<<"no non repeating character present\n"; else cout<<c<<endl; is that the correct way to return -1 when required character is not present?

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• Optional read from STDIN in C

  - by Yuval A

  My application is basically a shell which expects an input of type cmd [x], where cmd is constant and x is optional. So cmd 1 is legal as well as cmd by itself - then I assume a default parameter for x. I am doing this: char cmd[64]; scanf("%s", cmd); int arg; scanf("%d", &arg); // but this should be optional How can I read the integer parameter, and set it to a default if none is currently available in the prompt? I do not want the prompt to wait for additional input if it was not given in the original command. I tried several versions using fgetc() and getchar() and comparing them to EOF but to no avail. Each version I tried ends up waiting on that optional integer parameter.

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• how to clear XFixes regions

  - by ~buratinas

  Hi, I'm writing some low level code for X11 platform. To achieve best data copying performance I use XFixes/XDamage extensions. How can I clear the contents of XFixes region after one refresh cycle? Or do they clean themselves after I use XFixesSetPictureClipRegion? My code is something like that: Display xdpy; XShamPixmap pixmap_; XFixesRegion region_; damage_event_callback(damage_geometry_t geometry, XDamage damage,...) { unsigned curr_region = XFixesCreateRegion(xdpy, 0, 0); XDamageSubtract(xdpy, damage, None, curr_region); XFixesTranslateRegion( xdpy, curr_region, geometry.left(), geometry.top() ); XFixesUnionRegion (xdpy, region_, region_, curr_region); } process_damage_events(...) { XFixesSetPictureClipRegion( xdpy, pixmap_, 0, 0, region_); XCopyArea (xdpy, window_->id(), pixmap_, XDefaultGC(xdpy, XDefaultScreen(xdpy)), 0,0,width(),height(),0,0); /*Should clear region_ here */ ... } Currently I clear the region by deleting and recreating, but I guess it's not the best way to do that.

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• How to ensure that no non-ascii unicode characters are entered ?

  - by Jacques René Mesrine

  Given a java.lang.String instance, I want to verify that it doesn't contain any unicode characters that are not ASCII alphanumerics. e.g. The string should be limited to [A-Za-z0-9.]. What I'm doing now is something very inefficient: import org.apache.commons.lang.CharUtils; String s = ...; char[] ch = s.toCharArray(); for( int i=0; i<ch.length; i++) { if( ! CharUtils.isAsciiAlphanumeric( ch[ i ] ) throw new InvalidInput( ch[i] + " is invalid" ); } Is there a better way to solve this ?

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• 3 hash functions to best hash sliding window strings for a bloom filter with minimum collisions

  - by Duaa

  Hi all: I need 3 hash functions to hash strings of a sliding window moving over a text, to be used later to search within a bloom vector. I'm using C# in my programming I read something about rolling hash functions and cyclic polynomials, they are used for sliding window applications. But really, I did not find any codes, they are just descriptions So please, if anyone have any idea about 3 best C# hash functions to use with sliding window strings of fixed size (5-char), that consume less time and have minimum number of collisions, either they are rolling hash functions or others, please help me with some C# codes or links to hash functions names Duaa

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• translate ia32 into C

  - by David Lee

  I am trying to translate the following: Action: push %ebp #function prolog mov %esp, %ebp sub $0x10, %esp mov 0x8(%ebp), %eax #first line compiles to these 4 lines imul 0x8(%ebp), %eax sub $0x7, %eax mov %eax, -0x4(%ebp) addl $0x8, 0xc(%ebp) #second line mov -0x4(%ebp), %eax #third line mov 0xc(%ebp), %edx mov (%edx, %eax, 4), %eax add $0x3, %eax movb $0x41, (%eax) leave ret So far I have the following: //What am I missing? void Action(int x, char **y) { int z = x * x - 7; y+=8; //missing third line } What is the best way to translate this?

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• How to do timer with Nios II assembly?

  - by Nick Rosencrantz

  I've got an assignment in a computer engineering course that I don't fully understand since it is so large. Anyway I started coding the parts of it and it seems we should make code for some sort of timer. I've started put together the subroutine for snaptime but I'm not sure what I want: .equ timer, 0x920 .global snaptime .text .align 2 snaptime: movia r8,timer # basadressen till timern stw r0,12(r8) # sparar 0 till snapl movi r9,0b0110 # spara 6 i r9 stw r9,16(r8) # spara r9 movi ... ? andi r10,r10,0xFFFF The manual for Nios II assembly is here and the C code for what I'm trying to do is: #define TIMER_1_BASE ((volatile unsigned int*) 0x920) int snaptime (void) { int snaphight; int snaplow; int snap; TIMER_1_BASE[4]=0; snaphigh = TIMER_1_BASE[5] & 0xffffff; snaplow = TIMER_1_BASE[4] & 0xffffff; snap = snaphigh*65536+snaplow; return (snap); } Perhaps you can inspect the C which should be properly defined and see how I make it with assembly since the spec says it should be assembly.

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• Why does this MySQL function return null?

  - by Shore

  Description: the query actually run have 4 results returned,as can be see from below, what I did is just concate the items then return, but unexpectedly,it's null. I think the code is self-explanatory: DELIMITER | DROP FUNCTION IF EXISTS get_idiscussion_ask| CREATE FUNCTION get_idiscussion_ask(iask_id INT UNSIGNED) RETURNS TEXT DETERMINISTIC BEGIN DECLARE done INT DEFAULT 0; DECLARE body varchar(600); DECLARE created DATETIME; DECLARE anonymous TINYINT(1); DECLARE screen_name varchar(64); DECLARE result TEXT; DECLARE cur1 CURSOR FOR SELECT body,created,anonymous,screen_name from idiscussion left join users on idiscussion.uid=users.id where idiscussion.iask_id=iask_id; DECLARE CONTINUE HANDLER FOR SQLSTATE '02000' SET done = 1; SET result = ''; OPEN cur1; REPEAT FETCH cur1 INTO body, created, anonymous, screen_name; SET result = CONCAT(result,'<comment><body><![CDATA[',body,']]></body>','<replier>',if(screen_name is not null and !anonymous,screen_name,''),'</replier>','<created>',created,'</created></comment>'); UNTIL done END REPEAT; CLOSE cur1; RETURN result; END | DELIMITER ; mysql> DELIMITER ; mysql> select get_idiscussion_ask(1); +------------------------+ | get_idiscussion_ask(1) | +------------------------+ | NULL | +------------------------+ 1 row in set (0.01 sec) mysql> SELECT body,created,anonymous,screen_name from idiscussion left join users on idiscussion.uid=users.id where idiscussion.iask_id=1; +------+---------------------+-----------+-------------+ | body | created | anonymous | screen_name | +------+---------------------+-----------+-------------+ | haha | 2009-05-27 04:57:51 | 0 | NULL | | haha | 2009-05-27 04:57:52 | 0 | NULL | | haha | 2009-05-27 04:57:52 | 0 | NULL | | haha | 2009-05-27 04:57:53 | 0 | NULL | +------+---------------------+-----------+-------------+ 4 rows in set (0.00 sec) For those who don't think the code is self-explanatory: Why the function returns NULL?

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• dangling pointer, reason for value change after free()?

  - by Aman Jain

  In the following code segment, after free(x), why does y becomes 0? As per my understanding, the memory in the heap that was being pointed to by x, and is still being pointed by y, hasn't been allocated to someone else, so how can it change to 0? And moreover, I don't think it is free(x) that changed it to 0. Any comments? #include <stdio.h> int main ( int argc, char *argv[] ) { int *y = NULL; int *x = NULL; x = malloc(4); *x = 5; y = x; printf("[%d]\n", *y); //prints 5 free(x); printf("[%d]\n", *y); //why doesn't print 5?, prints 0 instead return 0; }

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• Python/C "defs" file - what is it?

  - by detly

  In the nautilus-python bindings, there is a file "nautilus.defs". It contains stanzas like (define-interface MenuProvider (in-module "Nautilus") (c-name "NautilusMenuProvider") (gtype-id "NAUTILUS_TYPE_MENU_PROVIDER") ) or (define-method get_mime_type (of-object "NautilusFileInfo") (c-name "nautilus_file_info_get_mime_type") (return-type "char*") ) Now I can see what most of these do (eg. that last one means that I can call the method "get_mime_type" on a "FileInfo" object). But I'd like to know: what is this file, exactly (ie. what do I search the web for to find out more info)? Is it a common thing to find in Python/C bindings? What is the format, and where is it documented? What program actually processes it? (So far, I've managed to glean that it gets transformed into a C source file, and it looks a bit like lisp to me.)

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