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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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  • 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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  • 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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  • [C] Programming problem: Storing values of an array in one variable

    - by OldMacDonald
    Hello, I am trying to use md5 code to calculate checksums of file. Now the given function prints out the (previously calculated) checksum on screen, but I want to store it in a variable, to be able to compare it later on. I guess the main problem is that I want to store the content of an array in one variable. How can I manage that? Probably this is a very stupid question, but maybe somone can help. Below is the function to print out the value. I want to modify it to store the result in one variable. static void MDPrint (mdContext) MD5_CTX *mdContext; { int i; for (i = 0; i < 16; i++) { printf ("%02x", mdContext->digest[i]); } // end of for } // end of function For reasons of completeness the used struct: /* typedef a 32 bit type */ typedef unsigned long int UINT4; /* Data structure for MD5 (Message Digest) computation */ typedef struct { UINT4 i[2]; /* number of _bits_ handled mod 2^64 */ UINT4 buf[4]; /* scratch buffer */ unsigned char in[64]; /* input buffer */ unsigned char digest[16]; /* actual digest after MD5Final call */ } MD5_CTX; and the used function to calculate the checksum: static int MDFile (filename) char *filename; { FILE *inFile = fopen (filename, "rb"); MD5_CTX mdContext; int bytes; unsigned char data[1024]; if (inFile == NULL) { printf ("%s can't be opened.\n", filename); return -1; } // end of if MD5Init (&mdContext); while ((bytes = fread (data, 1, 1024, inFile)) != 0) MD5Update (&mdContext, data, bytes); MD5Final (&mdContext); MDPrint (&mdContext); printf (" %s\n", filename); fclose (inFile); 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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  • 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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  • 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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  • This is a valid C code but not a valid C++ code?

    - by claws
    In some library I'm using (written in C) its StorePGM(image, width, height, filename) char *image; int width, height; char *filename; { // something something } All functions are defined this way. I never seen such function definitions in my life. They seem to be valid to MSVC but when I compile it as C++ it gives errors. What is it? some kind of old version C?

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  • C#: check if a string start with any character in a list

    - by JoesyXHN
    Hi, I want to check whether a string starts with any character in a list. My current implementation in C# is as follows: char[] columnChars = new char[] { 'A', 'B', 'C', 'D', 'E' }; private bool startWithColumn(string toCheck) { for(int i=0; i<columnChars.Length; i++) if (toCheck.StartsWith(columnChars[i]+"")) { return true; } return false; } I would like to know if any solution is better?

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  • "Implicit declaration" warning

    - by gcc
    For this code: int i=0; char **mainp; for(i=0;i<2;++i) { mainp[i]=malloc(sizeof(char)*200); if(!scanf("%[^#],#",mainp[i])) break; if(i<2) scanf("%[^#],#",mainp[i]); } GCC emits the warnings: warning: implicit declaration of function ‘scanf’ warning: incompatible implicit declaration of built-in function ‘scanf’ warning: ‘mainp’ may be used uninitialized in this function And I get a segmentation fault at runtime

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  • implicit declaration of

    - by gcc
    int i=0; char **mainp; for(i=0;i<2;++i) { mainp[i]=malloc(sizeof(char)*200); if(!scanf("%[^#],#",mainp[i])) break; if(i<2) scanf("%[^#],#",mainp[i]); } why does gcc send me that warnings warning: implicit declaration of function ‘scanf’ warning: incompatible implicit declaration of built-in function ‘scanf’ warning: ‘mainp’ may be used uninitialized in this function

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  • curl problems in c++ class

    - by Danilo
    I read a few articles on c++ / curl here on stackoverflow and assembled the following. The main goal is to handle the whole request in an instance of a class -- and maybe later in a secondary thread. My problem is: "content_" seems to stay empty though its the same addr and HttpFetch.h: class HttpFetch { private: CURL *curl; static size_t handle(char * data, size_t size, size_t nmemb, void * p); size_t handle_impl(char * data, size_t size, size_t nmemb); public: std::string content_; static std::string url_; HttpFetch(std::string url); void start(); std::string data(); }; HttpFetch.cpp: HttpFetch::HttpFetch(std::string url) { curl_global_init(CURL_GLOBAL_ALL); //pretty obvious curl = curl_easy_init(); content_.append("Test"); std::cout << &content_ << "\n"; curl_easy_setopt(curl, CURLOPT_URL, &url); curl_easy_setopt(curl, CURLOPT_WRITEDATA, &content_); curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, &HttpFetch::handle); //curl_easy_setopt(curl, CURLOPT_VERBOSE, 1L); //tell curl to output its progress curl_easy_setopt(curl, CURLOPT_FOLLOWLOCATION, 1L); //std::cout << &content_ << "\n"; } void HttpFetch::start() { curl_easy_perform(curl); curl_easy_cleanup(curl); } size_t HttpFetch::handle(char * data, size_t size, size_t nmemb, void * p) { std::string *stuff = reinterpret_cast<std::string*>(p); stuff->append(data, size * nmemb); std::cout << stuff << "\n"; // has content from data in it! return size * nmemb; } main.cpp: #include "HttpFetch.h" int main(int argc, const char * argv[]) { HttpFetch call = *new HttpFetch("http://www.example.com"); call.start(); ::std::cout << call.content_ << "\n" } Thanks in advance

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  • how does sizeof work with array in C++

    - by skydoor
    Hi, I was told the array name is a pointer char a[] = "a" but when sizeof(a) = 2 why not it is a size of pointer here? however when I define it like this char* a ="a"; we get sizeof(a) =4; Well, I think I need more information about how does sizeof work with the array names.... Can anyone elaborate that?

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  • Float to binary in C++

    - by Eric
    Hi, I'm wondering if there is a way to represent a float using a char in C++? For example: int main() { float test = 4.7567; char result = charRepresentation(test); return 0; } I read that probably using bitset I can do it but I'm not pretty sure.

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  • Regular expression - skip string in quotes using sed

    - by milano
    I have string like this: "Some standard text CONST_INSIDE_QUOTES" blah blah CONST "There might be another quotes" The thing is, that i want to replace all constants in string with some text, but it mustn't be applied on constants inside text in quotes. I have this regex: sed "s/([A-Z][A-Z0-9_]*)([^a-z])/<span class=\"const\"\1<\/span\2/g" which of course works for all consts. Any ideas how to exclude its apply on quotes constants? Unfortunately sed only...

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  • Remove control M from a text file in C

    - by Werner
    Hi, ist is possible? What would be the easiest way? I tried to compare in the input string character to character so if(char([i]=="^M") char[i]="" but it does not work. By the way, if I were able to check it, what is the wistes substitution? to "" ? Thanks

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  • Writting a getter for a pointer to a function .

    - by nomemory
    I have the following problem: "list.c" struct nmlist_element_s { void *data; struct nmlist_element_s *next; }; struct nmlist_s { nmlist_element *head; nmlist_element *tail; unsigned int size; void (*destructor)(void *data); int (*match)(const void *e1, const void *e2); }; /*** Other code ***/ What will be the signature for a function that returns 'destructor' ?

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