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• Flex (Lex, not actionscript or w/e) Error

  - by incrediman

  I'm totally new to flex. I'm getting a build error when using flex. That is, I've generated a .c file using flex, and, when running it, am getting this error: 1>lextest.obj : error LNK2001: unresolved external symbol "int __cdecl isatty(int)" (?isatty@@YAHH@Z) 1>C:\...\lextest.exe : fatal error LNK1120: 1 unresolved externals here is the lex file I'm using (grabbed from here): /*** Definition section ***/ %{ /* C code to be copied verbatim */ #include <stdio.h> %} /* This tells flex to read only one input file */ %option noyywrap %% /*** Rules section ***/ /* [0-9]+ matches a string of one or more digits */ [0-9]+ { /* yytext is a string containing the matched text. */ printf("Saw an integer: %s\n", yytext); } . { /* Ignore all other characters. */ } %% /*** C Code section ***/ int main(void) { /* Call the lexer, then quit. */ yylex(); return 0; } As well, why do I have to put a 'main' function in the lex syntax code? What I'd like is to be able to call yylex(); from another c file.

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• Lua Operator Overloading

  - by Pessimist

  I've found some places on the web saying that operators in Lua are overloadable but I can't seem to find any example. Can someone provide an example of, say, overloading the + operator to work like the .. operator works for string concatenation? EDIT 1: to Alexander Gladysh and RBerteig: If operator overloading only works when both operands are the same type and changing this behavior wouldn't be easy, then how come the following code works? (I don't mean any offense, I just started learning this language): printf = function(fmt, ...) io.write(string.format(fmt, ...)) end Set = {} Set.mt = {} -- metatable for sets function Set.new (t) local set = {} setmetatable(set, Set.mt) for _, l in ipairs(t) do set[l] = true end return set end function Set.union (a,b) -- THIS IS THE PART THAT MANAGES OPERATOR OVERLOADING WITH OPERANDS OF DIFFERENT TYPES -- if user built new set using: new_set = some_set + some_number if type(a) == "table" and type(b) == "number" then print("building set...") local mixedset = Set.new{} for k in pairs(a) do mixedset[k] = true end mixedset[b] = true return mixedset -- elseif user built new set using: new_set = some_number + some_set elseif type(b) == "table" and type(a) == "number" then print("building set...") local mixedset = Set.new{} for k in pairs(b) do mixedset[k] = true end mixedset[a] = true return mixedset end if getmetatable(a) ~= Set.mt or getmetatable(b) ~= Set.mt then error("attempt to 'add' a set with a non-set value that is also not a number", 2) end local res = Set.new{} for k in pairs(a) do res[k] = true end for k in pairs(b) do res[k] = true end return res end function Set.tostring (set) local s = "{" local sep = "" for e in pairs(set) do s = s .. sep .. e sep = ", " end return s .. "}" end function Set.print (s) print(Set.tostring(s)) end s1 = Set.new{10, 20, 30, 50} s2 = Set.new{30, 1} Set.mt.__add = Set.union -- now try to make a new set by unioning a set plus a number: s3 = s1 + 8 Set.print(s3) --> {1, 10, 20, 30, 50}

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• Mysqli query only works on localhost, not webserver

  - by whamo

  Hello. I have changed some of my old queries to the Mysqli framework to improve performance. Everything works fine on localhost but when i upload it to the webserver it outputs nothing. After connecting I check for errors and there are none. I also checked the php modules installed and mysqli is enabled. I am certain that it creates a connection to the database as no errors are displayed. (when i changed the database name string it gave the error) There is no output from the query on the webserver, which looks like this: $mysqli = new mysqli("server", "user", "password"); if (mysqli_connect_errno()) { printf("Can't connect Errorcode: %s\n", mysqli_connect_error()); exit; } // Query used $query = "SELECT name FROM users WHERE id = ?"; if ($stmt = $mysqli->prepare("$query")) { // Specify parameters to replace '?' $stmt->bind_param("d", $id); $stmt->execute(); // bind variables to prepared statement $stmt->bind_result($_userName); while ($stmt->fetch()) { echo $_userName; } $stmt-close(); } } //close connection $mysqli-close(); As I said this code works perfectly on my localserver just not online. Checked the error logs and there is nothing so everything points to a good connection. All the tables exists as well etc. Anyone any ideas because this one has me stuck! Also, if i get this working, will all my other queries still work? Or will i need to make them use the mysqli framework as well? Thanks in advance.

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• Can you tell me why this generates time limit exceeded in spoj(Prime Number Generator)

  - by magiix

  #include<iostream> #include<string.h> #include<math.h> using namespace std; bool prime[1000000500]; void generate(long long end) { memset(prime,true,sizeof(prime)); prime[0]=false; prime[1]=false; for(long long i=0;i<=sqrt(end);i++) { if(prime[i]==true) { for(long long y=i*i;y<=end;y+=i) { prime[y]=false; } } } } int main() { int n; long long b,e; scanf("%d",&n); while(n--) { cin>>b>>e; generate(e); for(int i=b;i<e;i++) { if(prime[i]) printf("%d\n",i); } } return 0; } That's my code for spoj prime generator. Altought it generates the same output as another accepted code ..

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• Call by Reference Function in C

  - by Chad

  Hello everyone, I would just like a push in the right direction here with my homework assignment. Here is the question: (1) Write a C function called input which returns void, this function prompts the user for input of two integers followed by a double precision value. This function reads these values from the keyboard and finds the product of the two integers entered. The function uses call by reference to communicate the values of the three values read and the product calculated back to the main program. The main program then prints the three values read and the product calculated. Provide test results for the input: 3 5 23.5. Do not use arrays or global variables in your program. And here is my code: #include <stdio.h> #include <stdlib.h> void input(int *day, int *month, double *k, double *pro); int main(void){ int i,j; double k, pro; input(&i, &j, &k, &pro); printf("%f\n", pro); return 0; } void input(int *i, int *j, double *k, double *pro){ int x,y; double z; double product; scanf("%d", &x); scanf("%d", &y); scanf("%f", &z); *pro += (x * y * z); } I can't figure out how to reference the variables with pointers really, it is just not working out for me. Any help would be great!

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• Perl to Ruby conversion (multidimensional arrays)

  - by Alex

  I'm just trying to get my head around a multidimensional array creation from a perl script i'm currently converting to Ruby, I have 0 experience in Perl, as in i opened my first Perl script this morning. Here is the original loop: my $tl = {}; for my $zoom ($zoommin..$zoommax) { my $txmin = lon2tilex($lonmin, $zoom); my $txmax = lon2tilex($lonmax, $zoom); # Note that y=0 is near lat=+85.0511 and y=max is near # lat=-85.0511, so lat2tiley is monotonically decreasing. my $tymin = lat2tiley($latmax, $zoom); my $tymax = lat2tiley($latmin, $zoom); my $ntx = $txmax - $txmin + 1; my $nty = $tymax - $tymin + 1; printf "Schedule %d (%d x %d) tiles for zoom level %d for download ...\n", $ntx*$nty, $ntx, $nty, $zoom unless $opt{quiet}; $tl->{$zoom} = []; for my $tx ($txmin..$txmax) { for my $ty ($tymin..$tymax) { push @{$tl->{$zoom}}, { xyz => [ $tx, $ty, $zoom ] }; } } } and what i have so far in Ruby: tl = [] for zoom in zoommin..zoommax txmin = cm.tiles.xtile(lonmin,zoom) txmax = cm.tiles.xtile(lonmax,zoom) tymin = cm.tiles.ytile(latmax,zoom) tymax = cm.tiles.ytile(latmin,zoom) ntx = txmax - txmin + 1 nty = tymax - tymin + 1 tl[zoom] = [] for tx in txmin..txmax for ty in tymin..tymax tl[zoom] << xyz = [tx,ty,zoom] puts tl end end end The part i'm unsure of is nested right at the root of the loops, push @{$tl->{$zoom}},{ xyz => [ $tx, $ty, $zoom ] }; I'm sure this will be very simple for a seasoned Perl programmer, thanks! `

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• Printing Arrays from Structs

  - by Carlll

  I've been stumped for a few hours on an exercise where I must use functions to build up an array inside a struct and print it. In my current program, it compiles but crashes upon running. #define LIM 10 typedef char letters[LIM]; typedef struct { int counter; letters words[LIM]; } foo; int main(int argc, char **argv){ foo apara; structtest(apara, LIM); print_struct(apara); } int structtest(foo *p, int limit){ p->counter = 0; int i =0; for(i; i< limit ;i++){ strcpy(p->words[p->counter], "x"); //only filling arrays with 'x' as an example p->counter ++; } return; I do believe it's due to my incorrect usage/combination of pointers. I've tried adjusting them, but either an 'incompatible types' error is produced, or the array is seemingly blank } void print_struct(foo p){ printf(p.words); } I haven't made it successfully up to the print_struct stage, but I'm unsure whether p.words is the correct item to be calling. In the output, I would expect the function to return an array of x's. I apologize in advance if I've made some sort of grievous "I should already know this" C mistake. Thanks for your help.

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• advanced Visual Studio kung-fu test -- Calling functions from the Immediate Window during debugging

  - by kizzx2

  I see some related questions have been asked, but they're either too advanced for me to grasp or lacking a step-by-step guide from start to finish (most of them end up being insider talk of their own experiment results). OK here it is, given this simple program: #include <stdio.h> #include <string.h> int main() { FILE * f; char buffer[100]; memset(buffer, 0, 100); fun(); f = fopen("main.cpp", "r"); fread(buffer, 1, 99, f); printf(buffer); fclose(f); return 0; } What it does is basically print itself (assume file name is main.cpp). Question How can I have it print another file, say foobar.txt without modifying the source code? It has something to do with running it through VS's, stepping through the functions and hijacking the FILE pointer right before fread() is called. No need to worry about leaking resources by calling fclose(). I tried the simple f = fopen("foobar.txt", "r") which gave CXX0017: Error: symbol "fopen" not found Any ideas? Edit I found out the solution accidentally on Debugging Mozilla on Windows FAQ. The correct command to put into the Immediate Window is f = {,,MSVCR100D}fopen("foo.txt", "r") However, it doesn't really answer this question: I still don't understand what is going on here. How to systematically find out the {,,MSVCR100D} part for any given method? I know the MSVCR version changes from system to system. How can I find that out? Could anyone explain the curly brace syntax, especially, what are those two commas doing there? Are there more hidden gems using this syntax?

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• Knight's tour / recursion

  - by Layne

  Hey, I'm trying to learn a little bit more about recursion but somehow I can't solve the knight's tour and I'm hoping someone can point out my logic error. public class main { static int fsize = 5; static int board[][] = new int[fsize][fsize]; static int[] sprung_x = {1,2,2,1,-1,-2,-2,-1}; static int[] sprung_y = {-2,-1,1,2,2,1,-1,-2}; static void SucheWeg(int schrittnummer, int x, int y) { board[x][y] = schrittnummer; if( schrittnummer == ((fsize*fsize)-1)) { for(int i = 0; i<fsize; i++) { for(int c=0; c<fsize; c++) { System.out.printf("%3d", board[i][c]); } System.out.println("\n"); } } else { for(int i = 0; i<8; i++) { for(int c = 0; c<8; c++) { if( (x+sprung_x[i]) >= 0 && (x+sprung_x[i]) < fsize && (y+sprung_y[c]) >= 0 && (y+sprung_y[c]) < fsize ) { if(board[x+sprung_x[i]][y+sprung_y[c]] == -1) { System.out.println("Move: "+schrittnummer + "\n"); SucheWeg(schrittnummer+1, (x+sprung_x[i]), (y+sprung_y[c])); } } } } board[x][y] = -1; } } public static void main(String[] args) { System.out.println("Begin: \n"); for(int i = 0; i<fsize; i++) { for(int c = 0; c<fsize; c++) { board[i][c] = -1; } } SucheWeg(0, 0, 0); System.out.println("\nEnd"); } }

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• Using pthread to perform matrix multiplication

  - by shadyabhi

  I have both matrices containing only ones and each array has 500 rows and columns. So, the resulting matrix should be a matrix of all elements having value 500. But, I am getting res_mat[0][0]=5000. Even other elements are also 5000. Why? #include<stdio.h> #include<pthread.h> #include<unistd.h> #include<stdlib.h> #define ROWS 500 #define COLUMNS 500 #define N_THREADS 10 int mat1[ROWS][COLUMNS],mat2[ROWS][COLUMNS],res_mat[ROWS][COLUMNS]; void *mult_thread(void *t) { /*This function calculates 50 ROWS of the matrix*/ int starting_row; starting_row = *((int *)t); starting_row = 50 * starting_row; int i,j,k; for (i = starting_row;i<starting_row+50;i++) for (j=0;j<COLUMNS;j++) for (k=0;k<ROWS;k++) res_mat[i][j] += (mat1[i][k] * mat2[k][j]); return; } void fill_matrix(int mat[ROWS][COLUMNS]) { int i,j; for(i=0;i<ROWS;i++) for(j=0;j<COLUMNS;j++) mat[i][j] = 1; } int main() { int n_threads = 10; //10 threads created bcos we have 500 rows and one thread calculates 50 rows int j=0; pthread_t p[n_threads]; fill_matrix(mat1); fill_matrix(mat2); for (j=0;j<10;j++) pthread_create(&p[j],NULL,mult_thread,&j); for (j=0;j<10;j++) pthread_join(p[j],NULL); printf("%d\n",res_mat[0][0]); return 0; }

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• What programming hack from your past are you most ashamed of?

  - by LeopardSkinPillBoxHat

  We've all been there (usually when we are young and inexperienced). Fixing it properly is too difficult, too risky or too time-consuming. So you go down the hack path. Which hack from your past are you most ashamed of, and why? I'm talking about the ones where you would be really embarrassed if someone could attribute the hack to you (quite easily if you are using revision control software). One hack per answer please. Mine was shortly after I started in my first job. I was working on a legacy C system, and there was this strange defect where a screen view failed to update properly under certain circumstances. I wasn't familiar with how to use the debugger at this time, so I added traces into the code to figure out what was going on. Then I realised that the defect didn't occur anymore with the traces in the code. I slowly backed out the traces one-by-one, until I realised that only a single trace was required to make the problem go away. My logic now would tell me that I was dealing with some sort of race-condition or timing related issue that the trace just "hid under the rug". But I checked in the code with the following line, and all was well: printf(""); Which hacks are you ashamed of?

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• how to access a type defined in one .ml file in another .ml file

  - by user339261

  Hi, I m very new to ocaml and i m facing the problem below, In a.ml a record type t is defined and is also defined transparently in a.mli, i.e. in d interface so that the type definition is available to all other files. a.ml also has a function, func, which returns a list of t. Now in another file, b.ml i m calling func, now obviously ocaml compiler wud nt be able to infer d type of objects stored in d list, for compiler its just a list. so in b.ml, i hav something like dis, let tlist = A.func in let vart = List.hd tlist in printf "%s\n" vart.name (name is a field in record t) Now here i get a compiler error sayin "Unbound record field label name" which makes sense as compiler can't infer d type of vart. my first question: how do I explicitly provide d type of vart as t here? i tried doing "let vart:A.t = " but got the same error. I also tried creating another function to fetch the first element of d list and mentioning return type as A.t, but then i got the "Unbound value A.t". I did this: let firstt = function [] - 0 | x :: _ - A.t x ;; The problem is compiler is unable to recognize A.t (a type) in b.ml but is able to recognize function A.func. If I remove A.t from the b.ml, i don'get any compiler errors. Please help, its urgent work. Thanks in advance! ~Tarun

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• Which languages support *recursive* function literals / anonymous functions?

  - by Hugh Allen

  It seems quite a few mainstream languages support function literals these days. They are also called anonymous functions, but I don't care if they have a name. The important thing is that a function literal is an expression which yields a function which hasn't already been defined elsewhere, so for example in C, &printf doesn't count. EDIT to add: if you have a genuine function literal expression <exp>, you should be able to pass it to a function f(<exp>) or immediately apply it to an argument, ie. <exp>(5). I'm curious which languages let you write function literals which are recursive. Wikipedia's "anonymous recursion" article doesn't give any programming examples. Let's use the recursive factorial function as the example. Here are the ones I know: JavaScript / ECMAScript can do it with callee: function(n){if (n<2) {return 1;} else {return n * arguments.callee(n-1);}} it's easy in languages with letrec, eg Haskell (which calls it let): let fac x = if x<2 then 1 else fac (x-1) * x in fac and there are equivalents in Lisp and Scheme. Note that the binding of fac is local to the expression, so the whole expression is in fact an anonymous function. Are there any others?

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• Compiling C lib and OCaml exe using it, all using ocamlfind

  - by Magnus

  I'm trying to work out how to use ocamlfind to compile a C library and an OCaml executable using that C library. I put together a set of rather silly example files. % cat sillystubs.c #include <stdio.h> #include <caml/mlvalues.h> #include <caml/memory.h> #include <caml/alloc.h> #include <caml/custom.h> value caml_silly_silly( value unit ) { CAMLparam1( unit ); printf( "%s\n", __FILE__ ); CAMLreturn( Val_unit ); } % cat silly.mli external silly : unit -> unit = "silly_silly" % cat foo.ml open Silly open String let _ = print_string "About to call into silly"; silly (); print_string "Called into silly" I believe the following is the way to compile up the library: % ocamlfind ocamlc -c sillystubs.c % ar rc libsillystubs.a sillystubs.o % ocamlfind ocamlc -c silly.mli % ocamlfind ocmalc -a -o silly.cma -ccopt -L${PWD} -cclib -lsillystubs Now I don't seem to be able to use the created library though: % ocamlfind ocamlc -custom -o foo foo.cmo silly.cma /usr/bin/ld: cannot find -lsillystubs collect2: ld returned 1 exit status File "_none_", line 1, characters 0-1: Error: Error while building custom runtime system The OCaml tools are somewhat mysterious to me, so any pointers would be most welcome.

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• GCC - How to realign stack?

  - by psihodelia

  I try to build an application which uses pthreads and __m128 SSE type. According to GCC manual, default stack alignment is 16 bytes. In order to use __m128, the requirement is the 16-byte alignment. My target CPU supports SSE. I use a GCC compiler which doesn't support runtime stack realignment (e.g. -mstackrealign). I cannot use any other GCC compiler version. My test application looks like: #include <xmmintrin.h> #include <pthread.h> void *f(void *x){ __m128 y; ... } int main(void){ pthread_t p; pthread_create(&p, NULL, f, NULL); } The application generates an exception and exits. After a simple debugging (printf "%p", &y), I found that the variable y is not 16-byte aligned. My question is: how can I realign the stack properly (16-byte) without using any GCC flags and attributes (they don't help)? Should I use GCC inline Assembler within this thread function f()?

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• What do these C operators mean?

  - by Melkhiah66

  I'm reading the book "Programming Challenges: The Programming Contest Training Manual" and are implementing a problem where I do not understand the use of operators c1 and the comparison if (n&1), someone could help me to know they mean? this is the example code #include <stdio.h> #define MAX_N 300 #define MAX_D 150 long cache[MAX_N/2][2]; void make_cache(int n,int d,int mode) { long tmp[MAX_D]; int i,count; for(i=0;i<MAX_D;i++) tmp[i]=0; tmp[0]=1;count=0; while(count<=n) { count++; for(i=(count&1);i<=d;i+=2) { if(i) tmp[i] = tmp[i-1] + tmp[i+1]; else if(!mode) tmp[0]=tmp[1]; else tmp[0]=0; } if((count&1)==(d&1)) cache[count>>1][mode]=tmp[d]; } } int main() { int n,d,i; long sum; while(1) { scanf("%d %d",&n,&d); if(n&1) sum=0; else if(d==1) sum=1; else if(n<(d<<1)) sum=0; else if(n==(d<<1)) sum=1; else { make_cache(n,d,0); make_cache(n,d,1); sum=0; for(i=0;i<=(n>>1);i++) sum+=cache[i][0]*cache[(n>>1)-i][1]; } printf("%ld\n",sum); } return 0; }

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• Java UnknownFormatConversionException

  - by user1672458

  The code below is throwing this error, and I'm not sure why. It's clearly a problem with outputting String.format to the str variable, but I don't know what's wrong with it. Exception in thread "main" java.util.UnknownFormatConversionException: Conversion = 'i' at java.util.Formatter$FormatSpecifier.conversion(Unknown Source) at java.util.Formatter$FormatSpecifier.<init>(Unknown Source) at java.util.Formatter.parse(Unknown Source) at java.util.Formatter.format(Unknown Source) at java.util.Formatter.format(Unknown Source) at java.lang.String.format(Unknown Source) at Donor.toString(Donor.java:41) at Donor.main(Donor.java:65) - import java.util.Scanner; public class Donor { public String name; public int age; public double donation; Donor() { //Initialized to these values for debugging name = "NoName"; age = 0; donation = 0; } Donor(String nameinit, int ageinit, double donationinit) { name = nameinit; age = ageinit; donation = donationinit; } public String toString() { String str = ""; str = String.format("%s-30%i-6$%d-20", name, age, donation); return str; } public static void main(String[] args) { Scanner input = new Scanner(System.in); String nameinit = null; int ageinit = -1; double donationinit = -1; String outp = null; System.out.print("Enter the donor's name: "); nameinit = input.nextLine(); System.out.print("Enter the donor's age: "); ageinit = input.nextInt(); System.out.print("Enter the donation amount: "); donationinit = input.nextDouble(); Donor d = new Donor(nameinit, ageinit, donationinit); outp = d.toString(); System.out.printf("%s30 %s6 %s10", "Name", "Age", "Donation"); System.out.print("\n" + outp); input.close(); } }

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• passing an array of structures (containing two mpz_t numbers) to a function

  - by jerome

  Hello, I'm working on some project where I use the type mpz_t from the GMP C library. I have some problems passing an array of structures (containing mpz_ts) adress to a function : I wille try to explain my problem with some code. So here is the structure : struct mpz_t2{ mpz_t a; mpz_t b; }; typedef struct mpz_t2 *mpz_t2; void petit_test(mpz_t2 *test[]) { printf("entering petit test function\n"); for (int i=0; i < 4; i++) { gmp_printf("test[%d]->a = %Zd and test[%d]->b = %Zd\n", test[i]->a, test[i]->b); } } /* IN MAIN FUNCTION */ mpz_t2 *test = malloc(4 * sizeof(mpz_t2 *)); for (int i=0; i < 4; i++) { mpz_t2_init(&test[i]); // if I pass test[i] : compiler error mpz_set_ui(test[i].a, i); //if test[i]->a compiler error mpz_set_ui(test[i].b, i*10); //same problem gmp_printf("%Zd\n", test[i].b); //prints correct result } petit_test(test); The programm prints the expected result (in main) but after entering the petit_test function produces a segmentation fault error. I would need to edit the mpz_t2 structure array in petit_test. I tried some other ways allocating and passing the array to the function but I didn't manage to get this right. If someone has a solution to this problem, I would be very thankfull! Regards, jérôme.

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• Keyboard input: how to separate keycodes received from user

  - by Iulian Serbanoiu

  Hello, I am writing an application involving user input from the keyboard. For doing it I use this way of reading the input: #include <stdio.h> #include <termios.h> #include <unistd.h> int mygetch( ) { struct termios oldt, newt; int ch; tcgetattr( STDIN_FILENO, &oldt ); newt = oldt; newt.c_lflag &= ~( ICANON | ECHO ); tcsetattr( STDIN_FILENO, TCSANOW, &newt ); ch = getchar(); tcsetattr( STDIN_FILENO, TCSANOW, &oldt ); return ch; } int main(void) { int c; do{ c = mygetch(); printf("%d\n",c); }while(c!='q'); return 0; } Everyting works fine for letters digits,tabs but when hiting DEL, LEFT, CTRL+LEFT, F8 (and others) I receive not one but 3,4,5 or even 6 characters. The question is: Is is possible to make a separation of these characters (to actually know that I only hit one key or key combination). What I would like is to have a function to return a single integer value for any type of input (letter, digit, F1-F12, DEl, PGUP, PGDOWN, CTRL+A, CTRL+ALT+A, ALT+LEFT, etc). Is this possible? I'm interested in an idea to to this, the language doesn't matter much, though I'd prefer perl or c. Thanks, Iulian

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• Compare sign of two doubles

  - by bobobobo

  What's the fastest way to compare sign on a double? I know that a double has a "sign bit" but I'm not sure if the way I'm "looking for it" in its binary rep is a good idea or not. Barring "portability" issues, can someone tell me what's going on with this code in MSVC++? #include <stdio.h> int main() { double z = 5.0 ; __int64 bitSign ; __int64 *ptr ; ptr = (__int64*)&z ; for( __int64 sh = 0 ; sh < 65 ; sh++ ) { bitSign = 1L << sh ; // Weird. it doesn't do 1. printf( "Bit# %d (%llx): %lld\n", sh, bitSign, ( (*ptr) & bitSign) ) ; } } First, why is starting at bit 32, even though I only shifted by one bit? Second, is it ok for me to check the 64th bit of a double to check its sign on MSVC++? Or is there a more preferred way?

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• Listing directories in Linux from C

  - by nunos

  I am trying to simulate linux command ls using linux api from c. Looking at the code it does make sense, but when I run it I get "stat error: No such file or directory". I have checked that opendir is working ok. I think the problem is in stat, which is returning -1 even though I think it should return 0. What am I missing? Thanks for your help. #include <stdio.h> #include <stdlib.h> #include <string.h> #include <dirent.h> #include <sys/stat.h> #include <errno.h> int main(int argc, char *argv[]) { DIR *dirp; struct dirent *direntp; struct stat stat_buf; char *str; if (argc != 2) { fprintf( stderr, "Usage: %s dir_name\n", argv[0]); exit(1); } if ((dirp = opendir( argv[1])) == NULL) { perror(argv[1]); exit(2); } while ((direntp = readdir( dirp)) != NULL) { if (stat(direntp->d_name, &stat_buf)==-1) { perror("stat ERROR"); exit(3); } if (S_ISREG(stat_buf.st_mode)) str = "regular"; else if (S_ISDIR(stat_buf.st_mode)) str = "directory"; else str = "other"; printf("%-25s - %s\n", direntp->d_name, str); } closedir(dirp); exit(0); }

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• Windows Task Scheduler: IAction.QueryInterface() returns an error I cannot find a definition for

  - by Sascha

  Hello I am attempting to schedule a task (to open an .exe at a specific time) using C++ win32. But at one specific point I am getting an error, I have searched & searched to try & find the definition of this error but I cannot find it? Do you know what this error means: Hexadecimal: 80004003 Decimal: 2147500035 I wont post the whole function because its rather long (unless you may need it to determine the error context?). The code I am using (that causes the error) is the following: // QI for the executable task pointer. hr = action -> QueryInterface( IID_IExecAction, (void**) execAction ); action -> Release(); if( FAILED(hr) ) { printf("QueryInterface call failed for IExecAction: %x %X %u \n", hr, hr, hr ); rootFolder -> Release(); task -> Release(); CoUninitialize(); return false; } The output is: QueryInterface call failed for IExecAction: 80004003 80004003 2147500035

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• Efficient splitting of elements in a field

  - by Gary

  I have a field in a text file exported from a database. The field contains addresses but sometimes they are quite long and the database allows them to contain multiple lines. When exported, the newline character gets replaced with a dollar sign like this: first part of very long address$second part of very long address$third part of very long address Not every address has multiple lines and no address contains more than three lines. The length of each line is variable. I'm massaging the data for import into MS Access which is used for a mailmerge. I want to split the field on the $ sign if it's there but if the field only contains 1 line, I want to set my two extra output fields to a zero length string so that I don't wind up with blank lines in the address when it gets printed. I have an awk file that's working correctly on all the other data in the textfile but I need to get this last bit working. I tried the below code. Aside from the fact that I get a syntax error at the else, I'm not sure this is a good way to do what I want. This is being done with gawk on Windows. BEGIN { FS = "|" } $1 != "HEADER" { if ($6 ~ /\$/) split($6, arr, "$") address = arr[1] addresstwo = arr[2] addressthree = arr[3] addressLength = length(address) addressTwoLength = length(addresstwo) addressThreeLength = length(addressthree) else { address = $6 addressLength = length($6) addresstwo = "" addressTwoLength = length(addresstwo) addressthree = "" addressThreeLength = length(addressthree) } printf("%*s\t%*s\t\%*s\n", addressLength, address, addressTwoLength, addresstwo, addressThreeLength, addressthree) }

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• How do I determine if a terminal is color-capable?

  - by asjo

  I would like to change a program to automatically detect whether a terminal is color-capable or not, so when I run said program from within a non-color capable terminal (say M-x shell in (X)Emacs), color is automatically turned off. I don't want to hardcode the program to detect TERM={emacs,dumb}. I am thinking that termcap/terminfo should be able to help with this, but so far I've only managed to cobble together this (n)curses-using snippet of code, which fails badly when it can't find the terminal: #include <stdlib.h> #include <curses.h> int main(void) { int colors=0; initscr(); start_color(); colors=has_colors() ? 1 : 0; endwin(); printf(colors ? "YES\n" : "NO\n"); exit(0); } I.e. I get this: $ gcc -Wall -lncurses -o hep hep.c $ echo $TERM xterm $ ./hep YES $ export TERM=dumb $ ./hep NO $ export TERM=emacs $ ./hep Error opening terminal: emacs. $ which is... suboptimal.

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• How can I work around the fact that in C++, sin(M_PI) is not 0?

  - by Adam Doyle

  In C++, const double Pi = 3.14159265; cout << sin(Pi); // displays: 3.58979e-009 it SHOULD display the number zero I understand this is because Pi is being approximated, but is there any way I can have a value of Pi hardcoded into my program that will return 0 for sin(Pi)? (a different constant maybe?) In case you're wondering what I'm trying to do: I'm converting polar to rectangular, and while there are some printf() tricks I can do to print it as "0.00", it still doesn't consistently return decent values (in some cases I get "-0.00") The lines that require sin and cosine are: x = r*sin(theta); y = r*cos(theta); BTW: My Rectangular - Polar is working fine... it's just the Polar - Rectangular Thanks! edit: I'm looking for a workaround so that I can print sin(some multiple of Pi) as a nice round number to the console (ideally without a thousand if-statements) edit: In case anyone's curious, this was what I landed on: double sin2(double theta) // in degrees { double s = sin(toRadians(theta)); if (fabs(s - (int)s) < 0.000001) { return floor(s + 0.5); } return s; } where toRadians() is a macro that converts to radians

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