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  • Different types for declaring pointer variables

    - by viswanathan
    Consider the below 2 declarations. appears next to the datatype and not next to variable char* ptr1, * ptr2, * ptr3; //all 3 are pointers appears next to the variable and not next to datatype char *ptr1,*ptr2,*ptr3; //again al 3 are pointers Is there any difference in intepretation between the 2 declarations. I know there is no difference in the variables. What is the rationale behind introducing void pointers?

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  • g++ compiler complains about conversions between related types (from int to enum, from void* to clas

    - by Slav
    g++ compiler complains about conversions between related types (from int to enum, from void* to class*, from const char* to unsigned char*, etc.). Compiler handles such convertions as errors and won't compile furthermore. It occurs only when I compile using Dev-C++ IDE, but when I compile the same code (using the compiler which Dev-C++ uses) such errors (even warnings) do not appears. How to mute errors of such types?

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  • What the best approach to iterate and "store" files over a directory in C (Linux) ?

    - by Andrei Ciobanu
    I have written a function that checks if to files are duplicates or not. This function signature is: int check_dup_memmap(char *f1_name, char *f2_name) It returns: (-1) - If something went wrong; (0) - If the two files are similar; (+1) - If the two files are different; The next step is to write a function that iterates through all the files in a certain directory,apply the previous function, and gives a report on every existing duplicates. Initially I've thought to write a function that generates a file with all the filenames in a certain directory and then, read that file again and gain and compare every two files. Here is that version of the function, that gets all the filenames in a certain directory. void *build_dir_tree(char *dirname, FILE *f) { DIR *cdir = NULL; struct dirent *ent = NULL; struct stat buf; if(f == NULL){ fprintf(stderr, "NULL file submitted. [build_dir_tree].\n"); exit(-1); } if(dirname == NULL){ fprintf(stderr, "NULL dirname submitted. [build_dir_tree].\n"); exit(-1); } if((cdir = opendir(dirname)) == NULL){ char emsg[MFILE_LEN]; sprintf(emsg, "Cannot open dir: %s [build_dir_tree]\t",dirname); perror(emsg); } chdir(dirname); while ((ent = readdir(cdir)) != NULL) { lstat(ent->d_name, &buf); if (S_ISDIR(buf.st_mode)) { if (strcmp(".", ent->d_name) == 0 || strcmp("..", ent->d_name) == 0) { continue; } build_dir_tree(ent->d_name, f); } else{ fprintf(f, "/%s/%s\n",util_get_cwd(),ent->d_name); } } chdir(".."); closedir(cdir); } Still I consider this approach a little inefficient, as I have to parse the file again and again. In your opinion what are other approaches should I follow: Write a datastructure and hold the files instead of writing them in the file ? I think for a directory with a lot of files, the memory will become very fragmented. Hold all the filenames in auto-expanding array, so that I can easy access every file by their index, because they will in a contiguous memory location. Map this file in memory using mmap() ? But mmap may fail, as the file gets to big. Any opinions on this. I want to choose the most efficient path, and access as few resources as possible. This is the requirement of the program... EDIT: Is there a way to get the numbers of files in a certain directory, without iterating through it ?

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  • question regarding pointer in c language

    - by din
    char *sample = "String Value"; &sample is a pointer to the pointer of "String Value" is the above statement right? If the above statement right, what is the equivalent of &sample if my declaration is char sample[] = "String Value"

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  • How to append to an array that contains blank spaces - Java

    - by Cameron Townley
    I'm trying to append to a char[] array that contains blank spaces on the end. The char array for example contains the characters 'aaa'. When I append the first time the method functions properly and outputs 'aaabbb'. The initial capacity of the array is set to 80 or multiples of 80. The second time I try and append my output looks like"aaabbb bbb". Any psuedocode would be great.

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  • StringIndexOutOfBoundsException: String index out of range 0

    - by Evan F
    I'm trying to write a program to take the first letter of the user input to generate a username. I'm trying to write it so that if the user leaves the input blank, then the letter that would otherwise be taken to generate the username defaults to the letter 'z'. Here is my full code: import java.util.Scanner; /** UsernameGenerator.java Generates a username based on the users inputs. @author: Evan Fravert */ public class UsernameGenerator { /** * Generates a username based on the users inputs. *@param args command line argument */ public static void main(String[] args) { // abcde String first; String middle; String last; String password1; String password2; int randomNum; randomNum = (int) (Math.random() * 1000) + 100; Scanner userInput = new Scanner(System.in); System.out.println("Please enter your first name:"); first = userInput.nextLine(); String firstLower = first.toLowerCase(); System.out.println("Please enter your middle name:"); middle = userInput.nextLine(); String middleLower = middle.toLowerCase(); System.out.println("Please enter your last name:"); last = userInput.nextLine(); int lastEnd = last.length()-1; String lastLower = last.toLowerCase(); System.out.println("Please enter your password:"); password1 = userInput.nextLine(); System.out.println("Please enter your password again:"); password2 = userInput.nextLine(); char firstLetter = firstLower.charAt(0); char middleLetter = middleLower.charAt(0); char lastLetter = lastLower.charAt(0); char lastLast = lastLower.charAt(lastEnd); if first.length() == 0) { firstLetter = 'z'; } else { firstLetter = firstLower.charAt(0); } System.out.println("Your username is " + firstLetter + "" + middleLetter + "" + lastLetter + "" + "" + lastLast + "" + randomNum); System.out.println("Your password is " + password1); System.out.println("Welcome " + first + " " + middle + " " + last + "!"); } }

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  • Can't get GetModuleFileNameA to work, keep getting error 'missing type specifier...'

    - by flavour404
    Hi, I am trying to use 'GetModuleFileNameA' but I keep getting the error 'c4430: missing type specifier - int assumed'. From reading the results from my google search I am guessing that it is from my use of NULL: char Filename[MAX_PATH]; //this is a char buffer GetModuleFileNameA(NULL, Filename, sizeof(Filename)); NULL is supposedly defined in #include stdio.h which I have included in my project, what am I doing wrong? Thanks.

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  • if string is alphabetically greater than other string in objective

    - by Jonathan
    I'm trying to use an if statement to work out which of 2 strings comes first alphabetically. Like with numbers and greater and less than: if (1 < 2) { just with strings: if(@"ahello" < @"bhello") { Or would I have to have a string containing all the letters and then check the index of the first char in each string and see which index is greater, and the index that is less than the other comes first in the alphabet and then if they are equal move on to the next char and repeat?

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  • Error building QtDeclarative with Qt 4.6.2 on Mac OS X

    - by Viet
    I tried hard to build QtDeclarative with Qt 4.6.2 on Mac OS X (Leopard) and did lots of Googling without finding any cure. Could anyone please help to solve this problem? Thanks. Here goes the error: Undefined symbols: "QObjectPrivate::isSignalConnected(int) const", referenced from: QmlGraphicsKeysAttachedPrivate::isConnected(char const*)in qmlgraphicsitem.o QmlGraphicsMouseRegionPrivate::isConnected(char const*)in qmlgraphicsmouseregion.o ld: symbol(s) not found collect2: ld returned 1 exit status make: *** [.obj/QtDeclarative.framework/QtDeclarative] Error 1

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  • g++ compiler complains about conversions between relative types (from int to enum, from void* to cla

    - by Slav
    g++ compiler complains about conversions between relative types (from int to enum, from void* to class*, from const char* to unsigned char*, etc.). Compiler handles such convertions as errors and won't compile furthermore. It occurs only when I compile using Dev-C++ IDE, but when I compile the same code (using the compiler which Dev-C++ uses) such errors (even warnings) do not appears. How to mute errors of such types?

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  • What's the easiest way to parse a string in C?

    - by Luca Matteis
    I have to parse this string in C: XFR 3 NS 207.46.106.118:1863 0 207.46.104.20:1863\r\n And be able to get the 207.46.106.118 part and 1863 part (the first ip address). I know I could go char by char and eventually find my way through it, but what's the easiest way to get this information, given that the IP address in the string could change to a different format (with less digits)?

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  • Messing with the stack in assembly and c++

    - by user246100
    I want to do the following: I have a function that is not mine (it really doesn't matter here but just to say that I don't have control over it) and that I want to patch so that it calls a function of mine, preserving the arguments list (jumping is not an option). What I'm trying to do is, to put the stack pointer as it was before that function is called and then call mine (like going back and do again the same thing but with a different function). This doesn't work straight because the stack becomes messed up. I believe that when I do the call it replaces the return address. So, I did a step to preserve the return address saving it in a globally variable and it works but this is not ok because I want it to resist to recursitivy and you know what I mean. Anyway, i'm a newbie in assembly so that's why I'm here. Please, don't tell me about already made software to do this because I want to make things my way. Of course, this code has to be compiler and optimization independent. My code (If it is bigger than what is acceptable please tell me how to post it): // A function that is not mine but to which I have access and want to patch so that it calls a function of mine with its original arguments void real(int a,int b,int c,int d) { } // A function that I want to be called, receiving the original arguments void receiver(int a,int b,int c,int d) { printf("Arguments %d %d %d %d\n",a,b,c,d); } long helper; // A patch to apply in the "real" function and on which I will call "receiver" with the same arguments that "real" received. __declspec( naked ) void patch() { _asm { // This first two instructions save the return address in a global variable // If I don't save and restore, the program won't work correctly. // I want to do this without having to use a global variable mov eax, [ebp+4] mov helper,eax push ebp mov ebp, esp // Make that the stack becomes as it were before the real function was called add esp, 8 // Calls our receiver call receiver mov esp, ebp pop ebp // Restores the return address previously saved mov eax, helper mov [ebp+4],eax ret } } int _tmain(int argc, _TCHAR* argv[]) { FlushInstructionCache(GetCurrentProcess(),&real,5); DWORD oldProtection; VirtualProtect(&real,5,PAGE_EXECUTE_READWRITE,&oldProtection); // Patching the real function to go to my patch ((unsigned char*)real)[0] = 0xE9; *((long*)((long)(real) + sizeof(unsigned char))) = (char*)patch - (char*)real - 5; // calling real function (I'm just calling it with inline assembly because otherwise it seems to works as if it were un patched // that is strange but irrelevant for this _asm { push 666 push 1337 push 69 push 100 call real add esp, 16 } return 0; }

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  • gets (variable)

    - by borlee
    can anyone tell me why gets(abc) works with char[] but not with int? int abc; char name[] = "lolrofl"; printf("Hello %s.\n",name); printf("\n "); fflush(stdin); gets (abc); printf("\n die zahl ist %i.\n",abc); system("Pause"); return(0);

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  • Thread feeding other MultiThreading

    - by alaamh
    I see it's easy to open pipe between two process using fork, but how we can passing open pipe to threads. Assume we need to pass out of PROGRAM A to PROGRAM B "may by more than one thread", PROGRAM B send his output to PROGRAM C #include <stdio.h> #include <stdlib.h> #include <pthread.h> struct targ_s { char* reader; }; void *thread1(void *arg) { struct targ_s *targ = (struct targ_s*) arg; int status, fd[2]; pid_t pid; pipe(fd); pid = fork(); if (pid == 0) { int fd = fileno( targ->fd_reader ); dup2(STDIN_FILENO, fd); close(fd[0]); dup2(fd[1], STDOUT_FILENO); close(fd[1]); execvp ("PROGRAM B", NULL); exit(1); } else { close(fd[1]); dup2(fd[0], STDIN_FILENO); close(fd[0]); execl("PROGRAM C", NULL); wait(&status); return NULL; } } int main(void) { FILE *fpipe; char *command = "PROGRAM A"; char buffer[1024]; if (!(fpipe = (FILE*) popen(command, "r"))) { perror("Problems with pipe"); exit(1); } char* outfile = "out.dat"; FILE* f = fopen (outfile, "wb"); int fd = fileno( f ); struct targ_s targ; targ.fd_reader = outfile; pthread_t thid; if (pthread_create(&thid, NULL, thread1, &targ) != 0) { perror("pthread_create() error"); exit(1); } int len; while (read(fpipe, buffer, sizeof (buffer)) != 0) { len = strlen(buffer); write(fd, buffer, len); } pclose(fpipe); return (0); }

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  • Simple doubt related to strings in C

    - by piemesons
    // The first example: char text[] = "henri"; char *p; p = text; *(p + 1) = 'E'; // Output = hEnri // Now If we want to remove the "e" ie hnri, we would go for????? *(p + 1)=????? Please dont say start copying the array. I am looking for the best solution

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  • execl doesn't work in a while(1) cicle, server side; C script

    - by Possa
    Hi guys, I have a problem with a little C script who should run as a server and launch a popup for every message arriving. The execl syntax is correct because if I try a little script with main() { execl(...); } it works. When I put it in a while(1) cicle it doesn't work. Everything else is working, like printf or string operation, but not the execl. Even if I fork it doesn't work. I really don't know what I can do ... can anyone help me? Thanks in advice for your help and sorry for my bad english. Here's the complete server C code. #include <arpa/inet.h> #include <netinet/in.h> #include <stdio.h> #include <stdlib.h> #include <sys/types.h> #include <sys/socket.h> #include <unistd.h> #include <string.h> #define BUFLEN 512 #define PORT 9930 void diep(char *s) { perror(s); exit(1); } int main() { struct sockaddr_in si_me, si_other; int s, i, slen=sizeof(si_other), broadcastPermission; char buf[100], zeni[BUFLEN]; if ((s=socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP))==-1) diep("socket"); broadcastPermission = 1; if (setsockopt(s, SOL_SOCKET, SO_BROADCAST, (void *) &broadcastPermission, sizeof(broadcastPermission)) < 0) diep("setsockopt() failed"); memset((char *) &si_me, 0, sizeof(si_me)); si_me.sin_family = AF_INET; si_me.sin_port = htons(PORT); si_me.sin_addr.s_addr = htonl(INADDR_ANY); if (bind(s, &si_me, sizeof(si_me))==-1) diep("bind"); while (1) { if (recvfrom(s, buf, BUFLEN, 0, &si_other, &slen)==-1) diep("recvfrom()"); //printf("Received packet from %s:%d\nData: %s\n", inet_ntoa(si_other.sin_addr), ntohs(si_other.sin_port), buf); strcpy(zeni, ""); strcat(zeni, "zenity --warning --title Hack!! --text "); strcat(zeni, buf); printf("cmd: %s\n", zeni); //system (zeni); execl("/usr/bin/zenity", "/usr/bin/zenity", "--warning", "--title", "Warn!", "--text", buf, (char *) NULL); } close(s); return 0; }

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  • Where is the error in my code?

    - by Lulu Larson
    /** Yields: a String that contains each capital Letter (in 'A'..'Z') whose representation is prime */ public static String primeChars() { String s = ""; // inv: s contains each capital in "A'..c-1 whose representation is prime for (char c = 'A'; c <= 'Z'; c=(char)(c+1)) { if (Loops.isPrime((int)c) == true) { s= s+1; } } // s contains each capital in 'A' ..'Z' whose rep is a prime return s; }

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  • probelm with recv() on a tcp connection

    - by michael
    Hi, I am simulating TCP communication on windows in C I have sender and a receiver communicating. sender sends packets of specific size to receiver. receiver gets them and send an ACK for each packet it received back to the sender. If the sender didn't get a specific packet (they are numbered in a header inside the packet) it sends the packet again to the receiver. Here is the getPacket function on the receiver side: //get the next packet from the socket. set the packetSize to -1 //if it's the first packet. //return: total bytes read // return: 0 if socket has shutdown on sender side, -1 error, else number of bytes received int getPakcet(char *chunkBuff,int packetSize,SOCKET AcceptSocket){ int totalChunkLen = 0; int bytesRecv=-1; bool firstTime=false; if (packetSize==-1) { packetSize=MAX_PACKET_LENGTH; firstTime=true; } int needToGet=packetSize; do { char* recvBuff; recvBuff = (char*)calloc(needToGet,sizeof(char)); if(recvBuff == NULL){ fprintf(stderr,"Memory allocation problem\n"); return -1; } bytesRecv = recv(AcceptSocket, recvBuff, needToGet, 0); if (bytesRecv == SOCKET_ERROR){ fprintf(stderr,"recv() error %ld.\n", WSAGetLastError()); totalChunkLen=-1; return -1; } if (bytesRecv == 0){ fprintf(stderr,"recv(): socket has shutdown on sender side"); return 0; } else if(bytesRecv > 0) { memcpy(chunkBuff + totalChunkLen,recvBuff,bytesRecv); totalChunkLen+=bytesRecv; } needToGet-=bytesRecv; } while ((totalChunkLen < packetSize) && (!firstTime)); return totalChunkLen; } i use firstTime because for the first time the receiver doesn't know the normal package size that the sender is going to send to it, so i use a MAX_PACKET_LENGTH to get a package and then set the normal package size to the num of bytes i have received my problem is the last package. it's size is less than the package size so lets say last package size is 2 and the normal package size is 4. so recv() gets two bytes, continues to the while condition, then totalChunkLen < packetSize because 2<4 so it iterates the loop again and the gets stuck in recv() because it's blocking because the sender has nothing to send. on the sender side i can't close the connection because i didn't ACK back, so it's kind of a deadlock. receiver is stuck because it's waiting for more packages but sender has nothing to send. i don't want to use a timeout for recv() or to insert a special character to the package header to mark that it is the last one what can i do ? thanks

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  • C Named pipe (fifo). Parent process gets stuck

    - by Blitzkr1eg
    I want to make a simple program, that fork, and the child writes into the named pipe and the parent reads and displays from the named pipe. The problem is that it enters the parent, does the first printf and then it gets weird, it doesn't do anything else, does not get to the second printf, it just ways for input in the console. #include <string.h> #include <stdlib.h> #include <stdio.h> #include <unistd.h> #include <sys/types.h> #include <sys/stat.h> #include <fcntl.h> void main() { char t[100]; mkfifo("myfifo",777); pid_t pid; pid = fork(); if (pid==0) { //execl("fifo2","fifo2",(char*)0); char r[100]; printf("scrie2->"); scanf("%s",r); int fp; fp = open("myfifo",O_WRONLY); write(fp,r,99); close(fp); printf("exit kid \n"); exit(0); } else { wait(0); printf("entered parent \n"); // <- this it prints // whats below this line apparently its not being executed int fz; printf("1"); fz = open("myfifo",O_RDONLY); printf("2"); printf("fd: %d",fz); char p[100]; int size; printf("------"); //struct stat *info; //stat("myfifo",info); printf("%d",(*info).st_size); read(fz,p,99); close(fz); printf("%s",p); printf("exit"); exit(0); } }

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  • Parameter pack argument consumption

    - by yuri kilochek
    It is possible to get the first element of the parameter pack like this template <typename... Elements> struct type_list { }; template <typename TypeList> struct type_list_first_element { }; template <typename FirstElement, typename... OtherElements> struct type_list_first_element<type_list<FirstElement, OtherElements...>> { typedef FirstElement type; }; int main() { typedef type_list<int, float, char> list; typedef type_list_first_element<list>::type element; return 0; } but not possible to similary get the last element like this template <typename... Elements> struct type_list { }; template <typename TypeList> struct type_list_last_element { }; template <typename LastElement, typename... OtherElements> struct type_list_last_element<type_list<OtherElements..., LastElement>> { typedef LastElement type; }; int main() { typedef type_list<int, float, char> list; typedef type_list_last_element<list>::type element; return 0; } with gcc 4.7.1 complaining: error: 'type' in 'struct type_list_last_element<type_list<int, float, char>>' does not name a type What paragraps from the standard describe this behaviour? It seems to me that template parameter packs are greedy in a sense that they consume all matching arguments, which in this case means that OtherElements consumes all three arguments (int, float and char) and then there is nothing left for LastElement so the compilation fails. Am i correct in the assumption? EDIT: To clarify: I am not asking how to extract the last element from the parameter pack, i know how to do that. What i actually want is to pick the pack apart from the back as opposed to the front, and as such recursing all the way to the back for each element would be ineffective. Apparentely reversing the sequence beforehand is the most sensible choice.

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