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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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  • 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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  • Does the compiler optimize the function parameters passed by value?

    - by Naveen
    Lets say I have a function where the parameter is passed by value instead of const-reference. Further, lets assume that only the value is used inside the function i.e. the function doesn't try to modify it. In that case will the compiler will be able to figure out that it can pass the value by const-reference (for performance reasons) and generate the code accordingly? Is there any compiler which does that?

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  • Using operator+ without leaking memory?

    - by xokmzxoo
    So the code in question is this: const String String::operator+ (const String& rhs) { String tmp; tmp.Set(this->mString); tmp.Append(rhs.mString); return tmp; } This of course places the String on the stack and it gets removed and returns garbage. And placing it on the heap would leak memory. So how should I do this?

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  • Null reference for first memory address between 0 - 65535

    - by Terry
    I would like to understand a bit more about memory and I was unable to find it from Google, please forgive me if this is silly question. How come the following code, accessing memory address 0(and up to 65535) in C# would throw NullReferenceException byte* pointer = (byte*)0; byte test = *pointer; Thanks a lot in advance!

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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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  • 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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  • Does binding temporary to a reference require a copy constructor in C++?

    - by vitaut
    Consider the following code: class A { A(const A&); public: A() {} }; int main() { const A &a = A(); } This code compiles fine with GCC, but fails to compile with Visual C++ with the following error: test.cc(8) : error C2248: 'A::A' : cannot access private member declared in class 'A' test.cc(2) : see declaration of 'A::A' test.cc(1) : see declaration of 'A' So is it necessary to have a copy constructor accessible when binding a temporary to a reference?

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  • Copying from istream never stops

    - by the_drow
    This bit of code runs infinitely: copy(istream_iterator<char>(cin), istream_iterator<char>(), back_inserter(buff)); The behavior I was expecting is that it will stop when I press enter. However it doesn't. buff is a vector of chars.

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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 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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  • Regular Expression Help

    - by Dave
    Looking for some help with a Regular Expression to do the following: Must be Alpha Char Must be at least 1 Char Must NOT be a specific value, e.g. != "Default" Thanks for any help, Dave

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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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  • 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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  • Can 'iterator' type just subclass 'const_iterator'?

    - by doublep
    After another question about iterators I'm having some doubts about custom containers. In my container, iterator is a subclass of const_iterator, so that I get conversion from non-const to const "for free". But is this allowed or are there any drawbacks or non-working scenarios for such a setup?

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  • String literals C++?

    - by Bad Man
    I need to do the following C# code in C++ (if possible). I have to const a long string with lots of freaking quotes and other stuff in it. const String _literal = @"I can use "quotes" inside here";

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  • why is strtof is always evaluating to HUGE_VAL?

    - by bstullkid
    What could be the issue here? It doesn't matter what number I choose for str, it is always 26815615859885194199148049996411692254958731641184786755447122887443528060147093953603748596333806855380063716372972101707507765623893139892867298012168192.00 char *str = "2.6"; printf("%f\n", strtof(str, (char**)NULL)); //prints 26815615859885194199148049996411692254958731641184786755447122887443528060147093953603748596333806855380063716372972101707507765623893139892867298012168192.00

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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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  • duplicate symbol error C++

    - by iSight
    Hi, I have added some const character in my file as under. The error i get is duplicate symbol _xyz(say). What is the problem with it and how could i get out of this. const char* xyz = "xyz"; class Abc { public: Abc() { } };

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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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  • C++ WCHAR: Cannot allocate an array of constant size 0

    - by Rosarch
    I'm trying to create a WCHAR: LONG bufferSize = foo.bar() + 1; WCHAR wszBaz[bufferSize]; The compiler issues an error: error C2057: expected constant expression error C2466: cannot allocate an array of constant size 0 error C2133: 'wszBaz' unknown size What am I doing wrong? UPDATE: I added const but it still gives the same error: const LONG bufferSize = foo.bar() + 1; WCHAR wszBaz[bufferSize];

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  • C++, is it possible to call a constructor directly, without new?

    - by osgx
    Hello Can I call constructor explicitly, without using new, if I already have a memory for object? // class Object1{char *str;public:Object1(char*str):str(str){puts("ctor");puts(str);};~Object1(){puts("dtor");puts(str);}}; Object1 ooo[2] = {Object1("I'm the first object"), Object1("I'm the 2nd")}; do_smth_useful(ooo); ooo[0].~Object1(); // call destructor ooo[0].Object1("I'm the 3rd object in place of first"); // ???? - reuse memory

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