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• Boost.MultiIndex: Are there way to share object between two processes?

  - by Arman

  Hello, I have a Boost.MultiIndex big array about 10Gb. In order to reduce the reading I thought there should be a way to keep the data in the memory and another client programs will be able to read and analyse it. What is the proper way to organize it? The array looks like: struct particleID { int ID;// real ID for particle from Gadget2 file "ID" block unsigned int IDf;// postition in the file particleID(int id,const unsigned int idf):ID(id),IDf(idf){} bool operator<(const particleID& p)const { return ID<p.ID;} unsigned int getByGID()const {return (ID&0x0FFF);}; }; struct ID{}; struct IDf{}; struct IDg{}; typedef multi_index_container< particleID, indexed_by< ordered_unique< tag<IDf>, BOOST_MULTI_INDEX_MEMBER(particleID,unsigned int,IDf)>, ordered_non_unique< tag<ID>,BOOST_MULTI_INDEX_MEMBER(particleID,int,ID)>, ordered_non_unique< tag<IDg>,BOOST_MULTI_INDEX_CONST_MEM_FUN(particleID,unsigned int,getByGID)> > > particlesID_set; Any ideas are welcome. kind regards Arman.

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• GCC, -O2, and bitfields - is this a bug or a feature?

  - by Rooke

  Today I discovered alarming behavior when experimenting with bit fields. For the sake of discussion and simplicity, here's an example program: #include <stdio.h> struct Node { int a:16 __attribute__ ((packed)); int b:16 __attribute__ ((packed)); unsigned int c:27 __attribute__ ((packed)); unsigned int d:3 __attribute__ ((packed)); unsigned int e:2 __attribute__ ((packed)); }; int main (int argc, char *argv[]) { Node n; n.a = 12345; n.b = -23456; n.c = 0x7ffffff; n.d = 0x7; n.e = 0x3; printf("3-bit field cast to int: %d\n",(int)n.d); n.d++; printf("3-bit field cast to int: %d\n",(int)n.d); } The program is purposely causing the 3-bit bit-field to overflow. Here's the (correct) output when compiled using "g++ -O0": 3-bit field cast to int: 7 3-bit field cast to int: 0 Here's the output when compiled using "g++ -O2" (and -O3): 3-bit field cast to int: 7 3-bit field cast to int: 8 Checking the assembly of the latter example, I found this: movl $7, %esi movl $.LC1, %edi xorl %eax, %eax call printf movl $8, %esi movl $.LC1, %edi xorl %eax, %eax call printf xorl %eax, %eax addq $8, %rsp The optimizations have just inserted "8", assuming 7+1=8 when in fact the number overflows and is zero. Fortunately the code I care about doesn't overflow as far as I know, but this situation scares me - is this a known bug, a feature, or is this expected behavior? When can I expect gcc to be right about this? Edit (re: signed/unsigned) : It's being treated as unsigned because it's declared as unsigned. Declaring it as int you get the output (with O0): 3-bit field cast to int: -1 3-bit field cast to int: 0 An even funnier thing happens with -O2 in this case: 3-bit field cast to int: 7 3-bit field cast to int: 8 I admit that attribute is a fishy thing to use; in this case it's a difference in optimization settings I'm concerned about.

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• Optimizing for speed - 4 dimensional array lookup in C

  - by Tiago

  I have a fitness function that is scoring the values on an int array based on data that lies on a 4D array. The profiler says this function is using 80% of CPU time (it needs to be called several million times). I can't seem to optimize it further (if it's even possible). Here is the function: unsigned int lookup_array[26][26][26][26]; /* lookup_array is a global variable */ unsigned int get_i_score(unsigned int *input) { register unsigned int i, score = 0; for(i = len - 3; i--; ) score += lookup_array[input[i]][input[i + 1]][input[i + 2]][input[i + 3]]; return(score) } I've tried to flatten the array to a single dimension but there was no improvement in performance. This is running on an IA32 CPU. Any CPU specific optimizations are also helpful. Thanks

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• x86 Assembly Question about outputting

  - by jdea

  My code looks like this _declspec(naked) void f(unsigned int input,unsigned int *output) { __asm{ push dword ptr[esp+4] call factorial pop ecx mov [output], eax //copy result ret } } __declspec(naked) unsigned int factorial(unsigned int n) { __asm{ push esi mov esi, dword ptr [esp+8] cmp esi, 1 jg RECURSE mov eax, 1 jmp END RECURSE: dec esi push esi call factorial pop esi inc esi mul esi END: pop esi ret } } Its a factorial function and I'm trying to output the answer after it recursively calculates the number that was passed in But what I get returned as an output is the same large number I keep getting Not sure about what is wrong with my output, by I also see this error CXX0030: Error: expression cannot be evaluated Thanks!

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• Audit Table using Triggers

  - by Jose

  DROP TABLE IF EXISTS `actividades`.`act_actividad_audit`; CREATE TABLE `actividades`.`act_actividad_audit` ( `fe_creacion` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP, `usr_digitador` char(10) NOT NULL, `ip_digitador` char(15) NOT NULL, `id_act_actividad` int(10) unsigned NOT NULL, `titulo` char(64) NOT NULL, `act_prioridad_id` int(10) unsigned NOT NULL, `act_motivo_id` int(10) unsigned NOT NULL, `detalle` text, `detalle_tecnico` text, `hostname_id` int(10) unsigned NOT NULL, `hostname_nombre` char(50) NOT NULL, `es_SMOP` tinyint(1) NOT NULL, `url_SMOP` text, `es_tecnico` tinyint(1) NOT NULL ) ENGINE=InnoDB DEFAULT CHARSET=latin1 COMMENT='Auditoria Actividad General'; I want to populate that audit table with a trigger but how can i send or fill the values for usr_digitador or ip_digitador if that values are on client side.? please help

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• why is my 3n+1 problem solution wrong?

  - by nunos

  I have recently started reading "Programming Challenges" book by S. Skiena and believe or not I am kind of stuck in the very first problem. Here's a link to the problem: 3n+1 problem Here's my code: #include <iostream> #include <vector> #include <algorithm> using namespace std; unsigned long calc(unsigned long n); int main() { int i, j, a, b, m; vector<int> temp; while (true) { cin >> i >> j; if (cin.fail()) break; if (i < j) { a = i; b = j; } else { a = j; b = i; } temp.clear(); for (unsigned int k = a; k != b; k++) { temp.push_back(calc(k)); } m = *max_element(temp.begin(), temp.end()); cout << i << ' ' << j << ' ' << m << endl; } } unsigned long calc(unsigned long n) { unsigned long ret = 1; while (n != 1) { if (n % 2 == 0) n = n/2; else n = 3*n + 1; ret++; } return ret; } I know the code is inefficient and I should not be using vectors to store the data. Anyway, I still would like to know what it's wrong with this, since, for me, it makes perfect sense, even though I am getting WA (wrong answer at programming challenges judge and RE (Runtime Error) at UVa judge). Thanks.

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• Why is a 16-bit register used with BSR instruction in this code snippet?

  - by sharptooth

  In this hardcore article there's a function find_maskwidth() that basically detects the number of bits required to represent itemCount dictinct values: unsigned int find_maskwidth( unsigned int itemCount ) { unsigned int maskWidth, count = itemCount; __asm { mov eax, count mov ecx, 0 mov maskWidth, ecx dec eax bsr cx, ax jz next inc cx mov maskWidth, ecx next: } return maskWidth; } the question is why do they use ax and cx registers instead of eax and ecx?

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• Why this base64 function stop working when increasing max length?

  - by flyout

  I am using this class to encode/decode text to base64. It works fine with MAX_LEN up to 512 but if I increase it to 1024 the decode function returns and empty var. This is the function: char* Base64::encode(char *src) { char* ptr = dst+0; unsigned triad; unsigned int d_len = MAX_LEN; memset(dst,'\0', MAX_LEN); unsigned s_len = strlen(src); for (triad = 0; triad < s_len; triad += 3) { unsigned long int sr = 0; unsigned byte; for (byte = 0; (byte<3)&&(triad+byte<s_len); ++byte) { sr <<= 8; sr |= (*(src+triad+byte) & 0xff); } sr <<= (6-((8*byte)%6))%6; // shift left to next 6bit alignment if (d_len < 4) return NULL; // error - dest too short *(ptr+0) = *(ptr+1) = *(ptr+2) = *(ptr+3) = '='; switch(byte) { case 3: *(ptr+3) = base64[sr&0x3f]; sr >>= 6; case 2: *(ptr+2) = base64[sr&0x3f]; sr >>= 6; case 1: *(ptr+1) = base64[sr&0x3f]; sr >>= 6; *(ptr+0) = base64[sr&0x3f]; } ptr += 4; d_len -= 4; } return dst; } Why could be causing this?

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• stl::map insert segmentation fault

  - by Jakub Czaplicki

  Why does this code stop with the segmentation fault : class MapFile { public: /* ... */ std::map <unsigned int, unsigned int> inToOut; }; bool SwitchMapFile::LoadMapFile( const wxString& fileName ) { /* ... */ inToOut.insert( std::make_pair(spmPort,fibreId) ); } but this one works fine : class MapFile { public: /* ... */ }; bool MapFile::LoadMapFile( const wxString& fileName ) { /* ... */ std::map <unsigned int, unsigned int> inToOut; inToOut.insert( std::make_pair(input,output) ); } ?

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• C++ non-member functions for nested template classes

  - by beldaz

  I have been writing several class templates that contain nested iterator classes, for which an equality comparison is required. As I believe is fairly typical, the comparison is performed with a non-member (and non-friend) operator== function. In doing so, my compiler (I'm using Mingw32 GCC 4.4 with flags -O3 -g -Wall) fails to find the function and I have run out of possible reasons. In the rather large block of code below there are three classes: a Base class, a Composed class that holds a Base object, and a Nested class identical to the Composed class except that it is nested within an Outer class. Non-member operator== functions are supplied for each. These classes are in templated and untemplated forms (in their own respective namespaces), with the latter equivalent to the former specialised for unsigned integers. In main, two identical objects for each class are compared. For the untemplated case there is no problem, but for the templated case the compiler fails to find operator==. What's going on? #include <iostream> namespace templated { template<typename T> class Base { T t_; public: explicit Base(const T& t) : t_(t) {} bool equal(const Base& x) const { return x.t_==t_; } }; template<typename T> bool operator==(const Base<T> &x, const Base<T> &y) { return x.equal(y); } template<typename T> class Composed { typedef Base<T> Base_; Base_ base_; public: explicit Composed(const T& t) : base_(t) {} bool equal(const Composed& x) const {return x.base_==base_;} }; template<typename T> bool operator==(const Composed<T> &x, const Composed<T> &y) { return x.equal(y); } template<typename T> class Outer { public: class Nested { typedef Base<T> Base_; Base_ base_; public: explicit Nested(const T& t) : base_(t) {} bool equal(const Nested& x) const {return x.base_==base_;} }; }; template<typename T> bool operator==(const typename Outer<T>::Nested &x, const typename Outer<T>::Nested &y) { return x.equal(y); } } // namespace templated namespace untemplated { class Base { unsigned int t_; public: explicit Base(const unsigned int& t) : t_(t) {} bool equal(const Base& x) const { return x.t_==t_; } }; bool operator==(const Base &x, const Base &y) { return x.equal(y); } class Composed { typedef Base Base_; Base_ base_; public: explicit Composed(const unsigned int& t) : base_(t) {} bool equal(const Composed& x) const {return x.base_==base_;} }; bool operator==(const Composed &x, const Composed &y) { return x.equal(y); } class Outer { public: class Nested { typedef Base Base_; Base_ base_; public: explicit Nested(const unsigned int& t) : base_(t) {} bool equal(const Nested& x) const {return x.base_==base_;} }; }; bool operator==(const Outer::Nested &x, const Outer::Nested &y) { return x.equal(y); } } // namespace untemplated int main() { using std::cout; unsigned int testVal=3; { // No templates first typedef untemplated::Base Base_t; Base_t a(testVal); Base_t b(testVal); cout << "a=b=" << testVal << "\n"; cout << "a==b ? " << (a==b ? "TRUE" : "FALSE") << "\n"; typedef untemplated::Composed Composed_t; Composed_t c(testVal); Composed_t d(testVal); cout << "c=d=" << testVal << "\n"; cout << "c==d ? " << (c==d ? "TRUE" : "FALSE") << "\n"; typedef untemplated::Outer::Nested Nested_t; Nested_t e(testVal); Nested_t f(testVal); cout << "e=f=" << testVal << "\n"; cout << "e==f ? " << (e==f ? "TRUE" : "FALSE") << "\n"; } { // Now with templates typedef templated::Base<unsigned int> Base_t; Base_t a(testVal); Base_t b(testVal); cout << "a=b=" << testVal << "\n"; cout << "a==b ? " << (a==b ? "TRUE" : "FALSE") << "\n"; typedef templated::Composed<unsigned int> Composed_t; Composed_t c(testVal); Composed_t d(testVal); cout << "c=d=" << testVal << "\n"; cout << "d==c ? " << (c==d ? "TRUE" : "FALSE") << "\n"; typedef templated::Outer<unsigned int>::Nested Nested_t; Nested_t e(testVal); Nested_t f(testVal); cout << "e=f=" << testVal << "\n"; cout << "e==f ? " << (e==f ? "TRUE" : "FALSE") << "\n"; // Above line causes compiler error: // error: no match for 'operator==' in 'e == f' } cout << std::endl; return 0; }

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• Help with simple linux shell implementation

  - by nunos

  I am implementing a simple version of a linux shell in c. I have succesfully written the parser, but I am having some trouble forking out the child process. However, I think the problem is due to arrays, pointers and such, because just started C with this project and am not still very knowledgable with them. I am getting a segmentation fault and don't know where from. Any help is greatly appreciated. #include <stdio.h> #include <stdlib.h> #include <unistd.h> #include <string.h> #include <sys/wait.h> #include <sys/types.h> #define MAX_COMMAND_LENGTH 250 #define MAX_ARG_LENGTH 250 typedef enum {false, true} bool; typedef struct { char **arg; char *infile; char *outfile; int background; } Command_Info; int parse_cmd(char *cmd_line, Command_Info *cmd_info) { char *arg; char *args[MAX_ARG_LENGTH]; int i = 0; arg = strtok(cmd_line, " "); while (arg != NULL) { args[i] = arg; arg = strtok(NULL, " "); i++; } int num_elems = i; if (num_elems == 0) return -1; cmd_info->infile = NULL; cmd_info->outfile = NULL; cmd_info->background = 0; int iarg = 0; for (i = 0; i < num_elems-1; i++) { if (!strcmp(args[i], "<")) { if (args[i+1] != NULL) cmd_info->infile = args[++i]; else return -1; } else if (!strcmp(args[i], ">")) { if (args[i+1] != NULL) cmd_info->outfile = args[++i]; else return -1; } else cmd_info->arg[iarg++] = args[i]; } if (!strcmp(args[i], "&")) cmd_info->background = true; else cmd_info->arg[iarg++] = args[i]; cmd_info->arg[iarg] = NULL; return 0; } void print_cmd(Command_Info *cmd_info) { int i; for (i = 0; cmd_info->arg[i] != NULL; i++) printf("arg[%d]=\"%s\"\n", i, cmd_info->arg[i]); printf("arg[%d]=\"%s\"\n", i, cmd_info->arg[i]); printf("infile=\"%s\"\n", cmd_info->infile); printf("outfile=\"%s\"\n", cmd_info->outfile); printf("background=\"%d\"\n", cmd_info->background); } void get_cmd(char* str) { fgets(str, MAX_COMMAND_LENGTH, stdin); str[strlen(str)-1] = '\0'; //apaga o '\n' do fim } pid_t exec_simple(Command_Info *cmd_info) { pid_t pid = fork(); if (pid < 0) { perror("Fork Error"); return -1; } if (pid == 0) { execvp(cmd_info->arg[0], cmd_info->arg); perror(cmd_info->arg[0]); exit(1); } return pid; } int main(int argc, char* argv[]) { while (true) { char cmd_line[MAX_COMMAND_LENGTH]; Command_Info cmd_info; printf(">>> "); get_cmd(cmd_line); if ( (parse_cmd(cmd_line, &cmd_info) == -1) ) return -1; parse_cmd(cmd_line, &cmd_info); if (!strcmp(cmd_info.arg[0], "exit")) exit(0); pid_t pid = exec_simple(&cmd_info); waitpid(pid, NULL, 0); } return 0; } Thanks.

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• How does sizeof calculate the size of structures

  - by Gearoid Murphy

  I know that a char and an int are calculated as being 8 bytes on 32 bit architectures due to alignment, but I recently came across a situation where a structure with 3 shorts was reported as being 6 bytes by the sizeof operator. Code is as follows: #include <iostream> using namespace std ; struct IntAndChar { int a ; unsigned char b ; }; struct ThreeShorts { unsigned short a ; unsigned short b ; unsigned short c ; }; int main() { cout<<sizeof(IntAndChar)<<endl; // outputs '8' cout<<sizeof(ThreeShorts)<<endl; // outputs '6', I expected this to be '8' return 0 ; } Compiler : g++ (Debian 4.3.2-1.1) 4.3.2. This really puzzles me, why isn't alignment enforced for the structure containing 3 shorts?

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• Problems getting foreign keys working in MySQL

  - by thehuby

  I've been trying to get a delete to cascade and it just doesn't seem to work. I'm sure I am missing something obvious, can anyone help me find it? I would expect a delete on the 'articles' table to trigger a delete on the corresponding rows in the 'article_section_lt' table. CREATE TABLE articles ( id INTEGER UNSIGNED PRIMARY KEY AUTO_INCREMENT, url_stub VARCHAR(255) NOT NULL UNIQUE, h1 VARCHAR(60) NOT NULL UNIQUE, title VARCHAR(60) NOT NULL, description VARCHAR(150) NOT NULL, summary VARCHAR(150) NOT NULL DEFAULT "", html_content TEXT, date DATE NOT NULL, updated TIMESTAMP DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP )ENGINE=INNODB; CREATE TABLE article_sections ( /* blog, news etc */ id INTEGER UNSIGNED PRIMARY KEY AUTO_INCREMENT, url_stub VARCHAR(255) NOT NULL UNIQUE, h1 VARCHAR(60) NOT NULL, title VARCHAR(60) NOT NULL, description VARCHAR(150) NOT NULL, summary VARCHAR(150) NOT NULL DEFAULT "", html_content TEXT NOT NULL DEFAULT "" )ENGINE=INNODB; CREATE TABLE article_section_lt ( fk_article_id INTEGER UNSIGNED NOT NULL REFERENCES articles(id) ON DELETE CASCADE, fk_article_section_id INTEGER UNSIGNED NOT NULL )ENGINE=INNODB;

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• Finding N contiguous zero bits in an integer to the left of the MSB position of another integer

  - by James Morris

  The problem is: given an integer val1 find the position of the highest bit set (Most Significant Bit) then, given a second integer val2 find a contiguous region of unset bits, with the minimum number of zero bits given by width to the left of the position (ie, in the higher bits). Here is the C code for my solution: typedef unsigned int t; unsigned const t_bits = sizeof(t) * CHAR_BIT; _Bool test_fit_within_left_of_msb( unsigned width, t val1, t val2, unsigned* offset_result) { unsigned offbit = 0; unsigned msb = 0; t mask; t b; while(val1 >>= 1) ++msb; while(offbit + width < t_bits - msb) { mask = (((t)1 << width) - 1) << (t_bits - width - offbit); b = val2 & mask; if (!b) { *offset_result = offbit; return true; } if (offbit++) /* this conditional bothers me! */ b <<= offbit - 1; while(b <<= 1) offbit++; } return false; } Aside from faster ways of finding the MSB of the first integer, the commented test for a zero offbit seems a bit extraneous, but necessary to skip the highest bit of type t if it is set. I have also implemented similar algorithms but working to the right of the MSB of the first number, so they don't require this seemingly extra condition. How can I get rid of this extra condition, or even, are there far more optimal solutions? Edit: Some background not strictly required. The offset result is a count of bits from the high bit, not from the low bit as maybe expected. This will be part of a wider algorithm which scans a 2D array for a 2D area of zero bits. Here, for testing, the algorithm has been simplified. val1 represents the first integer which does not have all bits set found in a row of the 2D array. From this the 2D version would scan down which is what val2 represents. Here's some output showing success and failure: t_bits:32 t_high: 10000000000000000000000000000000 ( 2147483648 ) --------- ----------------------------------- *** fit within left of msb test *** ----------------------------------- val1: 00000000000000000000000010000000 ( 128 ) val2: 01000001000100000000100100001001 ( 1091569929 ) msb: 7 offbit:0 + width: 8 = 8 mask: 11111111000000000000000000000000 ( 4278190080 ) b: 01000001000000000000000000000000 ( 1090519040 ) offbit:8 + width: 8 = 16 mask: 00000000111111110000000000000000 ( 16711680 ) b: 00000000000100000000000000000000 ( 1048576 ) offbit:12 + width: 8 = 20 mask: 00000000000011111111000000000000 ( 1044480 ) b: 00000000000000000000000000000000 ( 0 ) offbit:12 iters:10 ***** found room for width:8 at offset: 12 ***** ----------------------------------- *** fit within left of msb test *** ----------------------------------- val1: 00000000000000000000000001000000 ( 64 ) val2: 00010000000000001000010001000001 ( 268469313 ) msb: 6 offbit:0 + width: 13 = 13 mask: 11111111111110000000000000000000 ( 4294443008 ) b: 00010000000000000000000000000000 ( 268435456 ) offbit:4 + width: 13 = 17 mask: 00001111111111111000000000000000 ( 268402688 ) b: 00000000000000001000000000000000 ( 32768 ) ***** mask: 00001111111111111000000000000000 ( 268402688 ) offbit:17 iters:15 ***** no room found for width:13 ***** (iters is the count of iterations of the inner while loop)

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• how to add a function to that program, and call that function from the command line in the function

  - by user336291

  a#include "smallsh.h" /*include file for example*/ /*program buffers and work pointers*/ static char inpbuf[MAXBUF], tokbuf[2*MAXBUF], *ptr = inpbuf, *tok = tokbuf; userin(p) /*print prompt and read a line*/ char *p; { int c, count; /*initialization for later routines*/ ptr = inpbuf; tok = tokbuf; /*display prompt*/ printf("%s ",p); for(count = 0;;) { if((c = getchar()) == EOF) return(EOF); if(count<MAXBUF) inpbuf[count++] = c; if(c == '\n' && count <MAXBUF) { inpbuf[count] = '\0'; return(count); } /*if line too long restart*/ if(c == '\n') { printf("smallsh:input line too long\n"); count = 0; printf("%s",p); } } } gettok(outptr) /*get token and place into tokbuf*/ char **outptr; { int type; *outptr = tok; /*strip white space*/ for(;*ptr == ' ' || *ptr == '\t'; ptr++) ; *tok++ = *ptr; switch(*ptr++) { case '\n': type = EOL; break; case '&': type = AMPERSAND; break; case ';': type = SEMICOLON; break; case '#': type = POUND; break; default: type = ARG; while(inarg(*ptr)) *tok++ = *ptr++; } *tok++ = '\0'; return(type); } static char special[]= {' ', '\t', '&', ':', '\n', '\0'}; inarg(c) /*are we in an ordinary argument*/ char c; { char *wrk; for(wrk = special;*wrk != '\0';wrk++) if(c == *wrk) return(0); return(1); } #include "smallsh.h" procline() /*process input line*/ { char *arg[MAXARG+1]; /*pointer array for runcommand*/ int toktype; /*type of token in command*/ int narg; /*number of arguments so far*/ int type; /*FOREGROUND or BACKGROUND*/ for(narg = 0;;) { /*loop FOREVER*/ /*take action according to token type*/ switch(toktype = gettok(&arg[narg])) { case ARG: if(narg<MAXARG) narg++; break; case EOL: case SEMICOLON: case AMPERSAND: case POUND: type = (toktype == AMPERSAND) ? BACKGROUND : FOREGROUND; if(narg!=0) { arg[narg] = NULL; runcommand(arg, type); } if((toktype == EOL)||(toktype=POUND)) return; narg = 0; break; } } } #include "smallsh.h" /*execute a command with optional wait*/ runcommand(cline,where) char **cline; int where; { int pid, exitstat, ret; if((pid = fork()) <0) { perror("smallsh"); return(-1); } if(pid == 0) { /*child*/ execvp(*cline, cline); perror(*cline); exit(127); } /*code for parent*/ /*if background process print pid and exit*/ if(where == BACKGROUND) { printf("[Process id %d]\n", pid); return(0); } /*wait until process pid exists*/ while( (ret=wait(&exitstat)) != pid && ret != -1) ; return(ret == -1 ? -1 : exitstat); } #include "smallsh.h" char *prompt = "Command>"; /*prompt*/ main() { while(userin(prompt) != EOF) procline(); }

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• xerces-c: Xml parsing multiple files

  - by user459811

  I'm atempting to learn xerces-c and was following this tutorial online. http://www.yolinux.com/TUTORIALS/XML-Xerces-C.html I was able to get the tutorial to compile and run through a memory checker (valgrind) with no problems however when I made alterations to the program slightly, the memory checker returned some potential leak bytes. I only added a few extra lines to main to allow the program to read two files instead of one. int main() { string configFile="sample.xml"; // stat file. Get ambigious segfault otherwise. GetConfig appConfig; appConfig.readConfigFile(configFile); cout << "Application option A=" << appConfig.getOptionA() << endl; cout << "Application option B=" << appConfig.getOptionB() << endl; // Added code configFile = "sample1.xml"; appConfig.readConfigFile(configFile); cout << "Application option A=" << appConfig.getOptionA() << endl; cout << "Application option B=" << appConfig.getOptionB() << endl; return 0; } I was wondering why is it when I added the extra lines of code to read in another xml file, it would result in the following output? ==776== Using Valgrind-3.6.0 and LibVEX; rerun with -h for copyright info ==776== Command: ./a.out ==776== Application option A=10 Application option B=24 Application option A=30 Application option B=40 ==776== ==776== HEAP SUMMARY: ==776== in use at exit: 6 bytes in 2 blocks ==776== total heap usage: 4,031 allocs, 4,029 frees, 1,092,045 bytes allocated ==776== ==776== 3 bytes in 1 blocks are definitely lost in loss record 1 of 2 ==776== at 0x4C28B8C: operator new(unsigned long) (vg_replace_malloc.c:261) ==776== by 0x5225E9B: xercesc_3_1::MemoryManagerImpl::allocate(unsigned long) (MemoryManagerImpl.cpp:40) ==776== by 0x53006C8: xercesc_3_1::IconvGNULCPTranscoder::transcode(unsigned short const*, xercesc_3_1::MemoryManager*) (IconvGNUTransService.cpp:751) ==776== by 0x4038E7: GetConfig::readConfigFile(std::string&) (in /home/bonniehan/workspace/test/a.out) ==776== by 0x403B13: main (in /home/bonniehan/workspace/test/a.out) ==776== ==776== 3 bytes in 1 blocks are definitely lost in loss record 2 of 2 ==776== at 0x4C28B8C: operator new(unsigned long) (vg_replace_malloc.c:261) ==776== by 0x5225E9B: xercesc_3_1::MemoryManagerImpl::allocate(unsigned long) (MemoryManagerImpl.cpp:40) ==776== by 0x53006C8: xercesc_3_1::IconvGNULCPTranscoder::transcode(unsigned short const*, xercesc_3_1::MemoryManager*) (IconvGNUTransService.cpp:751) ==776== by 0x40393F: GetConfig::readConfigFile(std::string&) (in /home/bonniehan/workspace/test/a.out) ==776== by 0x403B13: main (in /home/bonniehan/workspace/test/a.out) ==776== ==776== LEAK SUMMARY: ==776== definitely lost: 6 bytes in 2 blocks ==776== indirectly lost: 0 bytes in 0 blocks ==776== possibly lost: 0 bytes in 0 blocks ==776== still reachable: 0 bytes in 0 blocks ==776== suppressed: 0 bytes in 0 blocks ==776== ==776== For counts of detected and suppressed errors, rerun with: -v ==776== ERROR SUMMARY: 2 errors from 2 contexts (suppressed: 2 from 2)

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• Ways to divide the high/low byte from a 16bit address?

  - by Grissiom

  Hello, I'm developing a software on 8051 processor. A frequent job is to divide the high and low byte of a 16bit address. I want to see there are how many ways to achieve it. The ways I come up so far are: (say ptr is a 16bit pointer, and int is 16bit int) ADDH = (unsigned int) ptr >> 8; ADDL = (unsigned int) ptr & 0x00FF; and ADDH = ((unsigned char *)&ptr)[0]; ADDL = ((unsigned char *)&ptr)[1]; Does anyone have any other bright ideas? ;) And anyone can tell me which way is more efficient?

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• A follow up on type coercion in C++, as it may be construed by type conversion

  - by David

  This is a follow up to my previous question. Consider that I write a function with the following prototype: int a_function(Foo val); Where foo is believed to be a type defined unsigned int. This is unfortunately not verifiable for lack of documentation. So, someone comes along and uses a_function, but calls it with an unsigned int as an argument. Here the story takes a turn. Foo turns out to actually be a class, which can take an unsigned int as a single argument of unsigned int in an explicit constructor. Is it a standard and reliable behavior for the compiler to render the function call by doing a type conversion on the argument. I.e. is the compiler supposed to recognize the mismatch and insert the constructor? Or should I get a compile time error reporting the type mismatch.

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• C++ Map of Vector of Structs?

  - by garsh0p

  So here's a snippet of my code: struct dv_nexthop_cost_pair { unsigned short nexthop; unsigned int cost; }; map<unsigned short, vector<struct dv_nexthop_cost_pair> > dv; I'm getting the following compiler error: error: ISO C++ forbids declaration of `map' with no type What's the proper way to declare this?

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• MySQL and INT auto_increment fields

  - by PHPguy

  Hello folks, I'm developing in LAMP (Linux+Apache+MySQL+PHP) since I remember myself. But one question was bugging me for years now. I hope you can help me to find an answer and point me into the right direction. Here is my challenge: Say, we are creating a community website, where we allow our users to register. The MySQL table where we store all users would look then like this: CREATE TABLE `users` ( `uid` int(2) unsigned NOT NULL auto_increment COMMENT 'User ID', `name` varchar(20) NOT NULL, `password` varchar(32) NOT NULL COMMENT 'Password is saved as a 32-bytes hash, never in plain text', `email` varchar(64) NOT NULL, `created` int(11) unsigned NOT NULL default '0' COMMENT 'Timestamp of registration', `updated` int(11) unsigned NOT NULL default '0' COMMENT 'Timestamp of profile update, e.g. change of email', PRIMARY KEY (`uid`) ) ENGINE=MyISAM DEFAULT CHARSET=utf8; So, from this snippet you can see that we have a unique and automatically incrementing for every new user 'uid' field. As on every good and loyal community website we need to provide users with possibility to completely delete their profile if they want to cancel their participation in our community. Here comes my problem. Let's say we have 3 registered users: Alice (uid = 1), Bob (uid = 2) and Chris (uid = 3). Now Bob want to delete his profile and stop using our community. If we delete Bob's profile from the 'users' table then his missing 'uid' will create a gap which will be never filled again. In my opinion it's a huge waste of uid's. I see 3 possible solutions here: 1) Increase the capacity of the 'uid' field in our table from SMALLINT (int(2)) to, for example, BIGINT (int(8)) and ignore the fact that some of the uid's will be wasted. 2) introduce the new field 'is_deleted', which will be used to mark deleted profiles (but keep them in the table, instead of deleting them) to re-utilize their uid's for newly registered users. The table will look then like this: CREATE TABLE `users` ( `uid` int(2) unsigned NOT NULL auto_increment COMMENT 'User ID', `name` varchar(20) NOT NULL, `password` varchar(32) NOT NULL COMMENT 'Password is saved as a 32-bytes hash, never in plain text', `email` varchar(64) NOT NULL, `is_deleted` int(1) unsigned NOT NULL default '0' COMMENT 'If equal to "1" then the profile has been deleted and will be re-used for new registrations', `created` int(11) unsigned NOT NULL default '0' COMMENT 'Timestamp of registration', `updated` int(11) unsigned NOT NULL default '0' COMMENT 'Timestamp of profile update, e.g. change of email', PRIMARY KEY (`uid`) ) ENGINE=MyISAM DEFAULT CHARSET=utf8; 3) Write a script to shift all following user records once a previous record has been deleted. E.g. in our case when Bob (uid = 2) decides to remove his profile, we would replace his record with the record of Chris (uid = 3), so that uid of Chris becomes qual to 2 and mark (is_deleted = '1') the old record of Chris as vacant for the new users. In this case we keep the chronological order of uid's according to the registration time, so that the older users have lower uid's. Please, advice me now which way is the right way to handle the gaps in the auto_increment fields. This is just one example with users, but such cases occur very often in my programming experience. Thanks in advance!

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• What is the meanning of 'idx_categories_desc_categories_name' in osCommerce

  - by Sumant

  while working on osCommerce-3 i got the table structure for category & categories_description as CREATE TABLE IF NOT EXISTS `osc_categories` ( `categories_id` int(10) unsigned NOT NULL AUTO_INCREMENT, `categories_image` varchar(255) DEFAULT NULL, `parent_id` int(10) unsigned DEFAULT NULL, `sort_order` int(11) DEFAULT NULL, `date_added` datetime DEFAULT NULL, `last_modified` datetime DEFAULT NULL, PRIMARY KEY (`categories_id`), KEY `idx_categories_parent_id` (`parent_id`) ) ENGINE=MyISAM DEFAULT CHARSET=utf8 AUTO_INCREMENT=5 ; CREATE TABLE IF NOT EXISTS `osc_categories_description` ( `categories_id` int(10) unsigned NOT NULL, `language_id` int(10) unsigned NOT NULL, `categories_name` varchar(255) NOT NULL, PRIMARY KEY (`categories_id`,`language_id`), KEY `idx_categories_desc_categories_id` (`categories_id`), KEY `idx_categories_desc_language_id` (`language_id`), KEY `idx_categories_desc_categories_name` (`categories_name`) ) ENGINE=MyISAM DEFAULT CHARSET=utf8; here i am not getting the meanning of indexing "idx_categories_desc_categories_id", "idx_categories_desc_language_id", "idx_categories_desc_categories_name" What is the use of this indexing.What does it mean?

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• C Programming: malloc() inside another function

  - by vikramtheone

  Hi Guys, I need help with malloc() inside another function. I'm passing a pointer and size to the function from my main() and I would like to allocate memory for that pointer dynamically using malloc() from inside that called function, but what I see is that.... the memory which is getting allocated is for the pointer declared withing my called function and not for the pointer which is inside the main(). How should I pass a pointer to a function and allocate memory for the passed pointer from inside the called function? Can anyone throw light on this? Help!!! Vikram I have written the following code and I get the output as shown below SOURCE: main() { unsigned char *input_image; unsigned int bmp_image_size = 262144; if(alloc_pixels(input_image, bmp_image_size)==NULL) printf("\nPoint2: Memory allocated: %d bytes",_msize(input_image)); else printf("\nPoint3: Memory not allocated"); } signed char alloc_pixels(unsigned char *ptr, unsigned int size) { signed char status = NO_ERROR; ptr = NULL; ptr = (unsigned char*)malloc(size); if(ptr== NULL) { status = ERROR; free(ptr); printf("\nERROR: Memory allocation did not complete successfully!"); } printf("\nPoint1: Memory allocated: %d bytes",_msize(ptr)); return status; } PROGRAM OUTPUT: Point1: Memory allocated ptr: 262144 bytes Point2: Memory allocated input_image: 0 bytes

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• SQL query to get latest record for all distinct items in a table

  - by David Buckley

  I have a table of all sales defined like: mysql> describe saledata; +-------------------+---------------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +-------------------+---------------------+------+-----+---------+-------+ | SaleDate | datetime | NO | | NULL | | | StoreID | bigint(20) unsigned | NO | | NULL | | | Quantity | int(10) unsigned | NO | | NULL | | | Price | decimal(19,4) | NO | | NULL | | | ItemID | bigint(20) unsigned | NO | | NULL | | +-------------------+---------------------+------+-----+---------+-------+ I need to get the last sale price for all items (as the price may change). I know I can run a query like: SELECT price FROM saledata WHERE itemID = 1234 AND storeID = 111 ORDER BY saledate DESC LIMIT 1 However, I want to be able to get the last sale price for all items (the ItemIDs are stored in a separate item table) and insert them into a separate table. How can I get this data? I've tried queries like this: SELECT storeID, itemID, price FROM saledata WHERE itemID IN (SELECT itemID from itemmap) ORDER BY saledate DESC LIMIT 1 and then wrap that into an insert, but it's not getting the proper data. Is there one query I can run to get the last price for each item and insert that into a table defined like: mysql> describe lastsale; +-------------------+---------------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +-------------------+---------------------+------+-----+---------+-------+ | StoreID | bigint(20) unsigned | NO | | NULL | | | Price | decimal(19,4) | NO | | NULL | | | ItemID | bigint(20) unsigned | NO | | NULL | | +-------------------+---------------------+------+-----+---------+-------+

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• MySQL query puzzle - finding what WOULD have been the most recent date

  - by Hank

  I've looked all over and haven't yet found an intelligent way to handle this, though I feel sure one is possible: One table of historical data has quarterly information: CREATE TABLE Quarterly ( unique_ID INT UNSIGNED NOT NULL, date_posted DATE NOT NULL, datasource TINYINT UNSIGNED NOT NULL, data FLOAT NOT NULL, PRIMARY KEY (unique_ID)); Another table of historical data (which is very large) contains daily information: CREATE TABLE Daily ( unique_ID INT UNSIGNED NOT NULL, date_posted DATE NOT NULL, datasource TINYINT UNSIGNED NOT NULL, data FLOAT NOT NULL, qtr_ID INT UNSIGNED, PRIMARY KEY (unique_ID)); The qtr_ID field is not part of the feed of daily data that populated the database - instead, I need to retroactively populate the qtr_ID field in the Daily table with the Quarterly.unique_ID row ID, using what would have been the most recent quarterly data on that Daily.date_posted for that data source. For example, if the quarterly data is 101 2009-03-31 1 4.5 102 2009-06-30 1 4.4 103 2009-03-31 2 7.6 104 2009-06-30 2 7.7 105 2009-09-30 1 4.7 and the daily data is 1001 2009-07-14 1 3.5 ?? 1002 2009-07-15 1 3.4 && 1003 2009-07-14 2 2.3 ^^ then we would want the ?? qtr_ID field to be assigned '102' as the most recent quarter for that data source on that date, and && would also be '102', and ^^ would be '104'. The challenges include that both tables (particularly the daily table) are actually very large, they can't be normalized to get rid of the repetitive dates or otherwise optimized, and for certain daily entries there is no preceding quarterly entry. I have tried a variety of joins, using datediff (where the challenge is finding the minimum value of datediff greater than zero), and other attempts but nothing is working for me - usually my syntax is breaking somewhere. Any ideas welcome - I'll execute any basic ideas or concepts and report back.

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• std::map insert segmentation fault

  - by Jakub Czaplicki

  Why does this code stop with segmentation fault : class MapFile { public: /* ... */ std::map <unsigned int, unsigned int> inToOut; }; bool MapFile::LoadMapFile( const wxString& fileName ) { /* ... */ inToOut.insert( std::make_pair(input,output) ); } but this one works fine : class MapFile { public: /* ... */ }; bool MapFile::LoadMapFile( const wxString& fileName ) { /* ... */ std::map <unsigned int, unsigned int> inToOut; inToOut.insert( std::make_pair(input,output) ); } ?

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