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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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  • Implicit conversion while using += operator?

    - by bdhar
    Conside the following code: int main() { signed char a = 10; a += a; // Line 5 a = a + a; return 0; } I am getting this warning at Line 5: d:\codes\operator cast\operator cast\test.cpp(5) : warning C4244: '+=' : conversion from 'int' to 'signed char', possible loss of data Does this mean that += operator makes an implicit cast of the right hand operator to int? P.S: I am using Visual studio 2005

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  • Most reliable split character

    - by JL
    Update If you were forced to use a single char on a split method, which char would be the most reliable? Definition of reliable: a split character that is not part of the individual sub strings being split.

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  • Get rid of Trailing Numbers in C

    - by Tech163
    For example, #include <stdio.h> int main (int argc, const char * argv[]) { char out = printf("teststring"); printf("%d\n", out); return 0; } will return teststring10. Anyone has an idea how to get rid of the 10? Thanks in advance.

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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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  • While within a switch block

    - by rursw1
    Hi, I've seen the following code, taken from the libb64 project. I'm trying to understand what is the purpose of the while loop within the switch block - switch (state_in->step) { while (1) { case step_a: do { if (codechar == code_in+length_in) { state_in->step = step_a; state_in->plainchar = *plainchar; return plainchar - plaintext_out; } fragment = (char)base64_decode_value(*codechar++); } while (fragment < 0); *plainchar = (fragment & 0x03f) << 2; case step_b: do { if (codechar == code_in+length_in) { state_in->step = step_b; state_in->plainchar = *plainchar; return plainchar - plaintext_out; } fragment = (char)base64_decode_value(*codechar++); } while (fragment < 0); *plainchar++ |= (fragment & 0x030) >> 4; *plainchar = (fragment & 0x00f) << 4; case step_c: do { if (codechar == code_in+length_in) { state_in->step = step_c; state_in->plainchar = *plainchar; return plainchar - plaintext_out; } fragment = (char)base64_decode_value(*codechar++); } while (fragment < 0); *plainchar++ |= (fragment & 0x03c) >> 2; *plainchar = (fragment & 0x003) << 6; case step_d: do { if (codechar == code_in+length_in) { state_in->step = step_d; state_in->plainchar = *plainchar; return plainchar - plaintext_out; } fragment = (char)base64_decode_value(*codechar++); } while (fragment < 0); *plainchar++ |= (fragment & 0x03f); } } What can give the while? It seems that anyway, always the switch will perform only one of the cases. Did I miss something? Thanks.

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  • SQLite MYSQL character encoding

    - by Lee Armstrong
    I have a strange situation where the following code works however XCode warns it is deprecated... NSString *col1 = [NSString stringWithCString:(char *)sqlite3_column_text(compiledStatement, 0)]; However as that is the deprecated method if I set an encoding the string comes out wrong! I have tried all the encodings but none work! NSString *col1 = [NSString stringWithCString:(char *)sqlite3_column_text(compiledStatement, 0) encoding:NSASCIIStringEncoding];

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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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  • VC++ Debugger expression

    - by user85917
    In debug | Immediate window, why do i get this error: szTemp is a local variable at {,,Util.dll}MySock.Write("%s",szTemp) CXX0017: Error: symbol "szTemp" not found int SomeFunction( ..) { char* szSQL = new char[1024]; . . ---> Breakpoint.. Trying to run the expression here.. . . }

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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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  • MSVC++ enum underlying type

    - by bobobobo
    MSDN has enum [tag] [: type] {enum-list} [declarator]; // for definition of enumerated type SO it looks like you can specify the type of an enum in MSVC++, but it doesn't seem to work for me: // want "underlying type" of this enum to be char. enum MyCharEnum : char { Val1 ='A', Val2 ='B', Val9 ='X' } ;

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  • C++ operator[ ] on integer litteral

    - by gregseth
    I found this piece of code: char a = 1["ABC"]; A few quick test led me to the fact it was the same than writing: char a = "ABC"[1]; Which seems far more logical to me. So my questions: Why is this notation valid? Is there any reason to write something that way?

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  • Another getcwd question...

    - by rubenvb
    Sorry to keep hammering on this, but I'm trying to learn :). Is this any good? And yes, I care about memory leaks. I can't find a decent way of preallocating the char*, because there simply seems to be no cross-platform way. const string getcwd() { char* a_cwd = getcwd(NULL,0); string s_cwd(a_cwd); free(a_cwd); return s_cwd; }

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  • What's the fastest lookup algorithm for a key, pair data structure (i.e, a map)?

    - by truncheon
    In the following example a std::map structure is filled with 26 values from A - Z (for key) and 0 – 26 for value. The time taken (on my system) to lookup the last entry (10000000 times) is roughly 250 ms for the vector, and 125 ms for the map. (I compiled using release mode, with O3 option turned on for g++ 4.4) But if for some odd reason I wanted better performance than the std::map, what data structures and functions would I need to consider using? I apologize if the answer seems obvious to you, but I haven't had much experience in the performance critical aspects of C++ programming. #include <ctime> #include <map> #include <vector> #include <iostream> struct mystruct { char key; int value; mystruct(char k = 0, int v = 0) : key(k), value(v) { } }; int find(const std::vector<mystruct>& ref, char key) { for (std::vector<mystruct>::const_iterator i = ref.begin(); i != ref.end(); ++i) if (i->key == key) return i->value; return -1; } int main() { std::map<char, int> mymap; std::vector<mystruct> myvec; for (int i = 'a'; i < 'a' + 26; ++i) { mymap[i] = i - 'a'; myvec.push_back(mystruct(i, i - 'a')); } int pre = clock(); for (int i = 0; i < 10000000; ++i) { find(myvec, 'z'); } std::cout << "linear scan: milli " << clock() - pre << "\n"; pre = clock(); for (int i = 0; i < 10000000; ++i) { mymap['z']; } std::cout << "map scan: milli " << clock() - pre << "\n"; return 0; }

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  • C++ sort array of strings

    - by user69514
    I am trying to sort an array of strings, but it's not sorting anything.... what am I doing wrong? string namesS[MAX_NAMES]; int compare (const void * a, const void * b){ return ( *(char*)a - *(char*)b ); } void sortNames(){ qsort(namesS, MAX_NAMES, sizeof(string), compare); }

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  • How can I obtain the IP address of my server program?

    - by Dr Dork
    Hello! This question is related to another question I just posted. I'm prepping for a simple work project and am trying to familiarize myself with the basics of socket programming in a Unix dev environment. At this point, I have some basic server side code and client side code setup to communicate. Currently, my client code successfully connects to the server code and the server code sends it a test message, then both quit out. Perfect! That's exactly what I wanted to accomplish. Now I'm playing around with the functions used to obtain info about the two environments (server and client). I'd like to obtain my server program's IP address. Here's the code I currently have to do this, but it's not working... int sockfd; unsigned int len; socklen_t sin_size; char msg[]="test message"; char buf[MAXLEN]; int st, rv; struct addrinfo hints, *serverinfo, *p; struct sockaddr_storage client; char s[INET6_ADDRSTRLEN]; char ip[INET6_ADDRSTRLEN]; //zero struct memset(&hints,0,sizeof(hints)); hints.ai_family = AF_UNSPEC; hints.ai_socktype = SOCK_STREAM; hints.ai_flags = AI_PASSIVE; //get the server info if((rv = getaddrinfo(NULL, SERVERPORT, &hints, &serverinfo ) != 0)){ perror("getaddrinfo"); exit(-1); } // loop through all the results and bind to the first we can for( p = serverinfo; p != NULL; p = p->ai_next) { //Setup the socket if( (sockfd = socket( p->ai_family, p->ai_socktype, p->ai_protocol )) == -1 ) { perror("socket"); continue; } //Associate a socket id with an address to which other processes can connect if(bind(sockfd, p->ai_addr, p->ai_addrlen) == -1){ close(sockfd); perror("bind"); continue; } break; } if( p == NULL ){ perror("Fail to bind"); } inet_ntop(p->ai_family, get_in_addr((struct sockaddr *)p->ai_addr), s, sizeof(s)); printf("Server has TCP Port %s and IP Address %s\n", SERVERPORT, s); and the output for the IP is always empty... server has TCP Port 21412 and IP Address :: any ideas for what I'm missing? thanks in advance for your help! this stuff is really complicated at first.

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  • C problem, left of '->' must point to class/struct/union/generic type ??

    - by Patrick
    Hello! Trying to understand why this doesn't work. I keep getting the following errors: left of '-nextNode' must point to class/struct/union/generic type (Also all the lines with a - in the function new_math_struct) Header file #ifndef MSTRUCT_H #define MSTRUCT_H #define PLUS 0 #define MINUS 1 #define DIVIDE 2 #define MULTIPLY 3 #define NUMBER 4 typedef struct math_struct { int type_of_value; int value; int sum; int is_used; struct math_struct* nextNode; } ; typedef struct math_struct* math_struct_ptr; #endif C file int get_input(math_struct_ptr* startNode) { /* character, input by the user */ char input_ch; char* input_ptr; math_struct_ptr* ptr; math_struct_ptr* previousNode; input_ptr = &input_ch; previousNode = startNode; /* as long as input is not ok */ while (1) { input_ch = get_input_character(); if (input_ch == ',') // Carrage return return 1; else if (input_ch == '.') // Illegal character return 0; if (input_ch == '+') ptr = new_math_struct(PLUS, 0); else if (input_ch == '-') ptr = new_math_struct(MINUS, 0); else if (input_ch == '/') ptr = new_math_struct(DIVIDE, 0); else if (input_ch == '*') ptr = new_math_struct(MULTIPLY, 0); else ptr = new_math_struct(NUMBER, atoi(input_ptr)); if (startNode == NULL) { startNode = previousNode = ptr; } else { previousNode->nextNode = ptr; previousNode = ptr; } } return 0; } math_struct_ptr* new_math_struct(int symbol, int value) { math_struct_ptr* ptr; ptr = (math_struct_ptr*)malloc(sizeof(math_struct_ptr)); ptr->type_of_value = symbol; ptr->value = value; ptr->sum = 0; ptr->is_used = 0; return ptr; } char get_input_character() { /* character, input by the user */ char input_ch; /* get the character */ scanf("%c", &input_ch); if (input_ch == '+' || input_ch == '-' || input_ch == '*' || input_ch == '/' || input_ch == ')') return input_ch; // A special character else if (input_ch == '\n') return ','; // A carrage return else if (input_ch < '0' || input_ch > '9') return '.'; // Not a number else return input_ch; // Number } The header for the C file just contains a reference to the struct header and the definitions of the functions. Language C.

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  • can't read from stream until child exits?

    - by BobTurbo
    OK I have a program that creates two pipes - forks - the child's stdin and stdout are redirected to one end of each pipe - the parent is connected to the other ends of the pipes and tries to read the stream associated with the child's output and print it to the screen (and I will also make it write to the input of the child eventually). The problem is, when the parent tries to fgets the child's output stream, it just stalls and waits until the child dies to fgets and then print the output. If the child doesn't exit, it just waits forever. What is going on? I thought that maybe fgets would block until SOMETHING was in the stream, but not block all the way until the child gives up its file descriptors. Here is the code: #include <stdlib.h> #include <stdio.h> #include <string.h> #include <sys/types.h> #include <unistd.h> int main(int argc, char *argv[]) { FILE* fpin; FILE* fpout; int input_fd[2]; int output_fd[2]; pid_t pid; int status; char input[100]; char output[100]; char *args[] = {"/somepath/someprogram", NULL}; fgets(input, 100, stdin); // the user inputs the program name to exec pipe(input_fd); pipe(output_fd); pid = fork(); if (pid == 0) { close(input_fd[1]); close(output_fd[0]); dup2(input_fd[0], 0); dup2(output_fd[1], 1); input[strlen(input)-1] = '\0'; execvp(input, args); } else { close(input_fd[0]); close(output_fd[1]); fpin = fdopen(input_fd[1], "w"); fpout = fdopen(output_fd[0], "r"); while(!feof(fpout)) { fgets(output, 100, fpout); printf("output: %s\n", output); } } return 0; }

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  • How initialize array of classes? (C++)

    - by Kra
    Hello, I have this class constructor: Pairs (int Pos, char *Pre, char *Post, bool Attach = true); How can I initialize array of Pairs classes? I tried: Pairs Holder[3] = { {Input.find("as"), "Pre", "Post"}, {Input.find("as"), "Pre", "Post"}, {Input.find("as"), "Pre", "Post"} }; Apparently it's not working, I also tried to use () brackets instead of {} but compiler keeps moaning all the time. Sorry if it is lame question, I googled quite hard but wasn't able to find answer :/ Thanks.

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  • Determining if types alias to the same underlying type in C++

    - by emchristiansen
    I'd like to write a templated function which changes its behavior depending on template class types passed in. To do this, I'd like to determine the type passed in. For example, something like this: template <class T> void foo() { if (T == int) { // Sadly, this sort of comparison doesn't work printf("Template parameter was int\n"); } else if (T == char) { printf("Template parameter was char\n"); } } Is this possible?

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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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  • What does this pointer-heavy C code do?

    - by justRadojko
    Could someone explain to me what should two following lines do: s.httpheaderline[s.httpheaderlineptr] = *(char *)uip_appdata; ++((char *)uip_appdata); This is taken from uIP code for microcontrollers. s - structure httpheaderline - http packet presented as a string httpheadrlineptr - integer value uip_appdata - received ethernet packet (string) If some more info is needed please let me know. BTW. Eclipse is reporting an error on the second line with message Invalid lvalue in increment so i'm trying to figure out how to solve this.

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  • Variable table or column names.

    - by Frank Computer
    INFORMIX-SQL or any other SQL-based DB: Suppose I have an app where depending on the value of some columns, example: company.code char(3) {abc} company.brach char(2) {01} Can I construct table name "abc01" for inclusion in SELECT * FROM abc01; ? In other words, a variable table name.. same question applies for column names.

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