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• why C clock() returns 0

  - by eddy ed

  I've got something like this: clock_t start, end; start=clock(); something_else(); end=clock(); printf("\nClock cycles are: %d - %d\n",start,end); and I always get as an output "Clock cycles are: 0 - 0" Any idea why this happens? (Just to give little detail, the something_else() function performs a left-to-right exponentiation using montgomery represantation, moreover I don't know for certain that the something_else() function does indeed take some not negligible time.) This is on Linux. The result of uname -a is: Linux snowy.*****.ac.uk 2.6.32-71.el6.x86_64 #1 SMP Fri May 20 03:51:51 BST 2011 x86_64 x86_64 x86_64 GNU/Linux

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• which is time consuming construct in following program?

  - by user388338

  while submitting a solution for practise problem 6(odd) i got TLE error but while using using print and scanf in place cin and cout my sol was submitted successfully with 0.77s time..i want to know how can i make it more efficient link to problem is codechef problem 6 #include<iostream> #include<cstdio> using namespace std; int main() {int n,N; scanf("%d",&n); for(int l=0;l<n;l++) { scanf("%d",&N); int i=0,x; if(N<=0) continue; for(;N>=(x=(2<<i));i++); printf("%d",x/2); cout<<"\n"; } }

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• I just can't figure out strcat.

  - by Anonymous

  I know I shouldn't be using that function, and I don't care. Last time I checked the spec for strcat, it said something along the lines of updating the first value as well as returning the same. Now, this is a really stupid question, and I want you to explain it like you're talking to a really stupid person. Why won't this work? char* foo="foo"; printf(strcat(foo,"bar")); EDIT: I don't know the difference between char[] and char*. How would I allocate a string of 255 characters? EDIT 2: OK, OK, so char[number] allocates a string of that many bytes? Makes sense. Thanks.

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• Testing for the presence of a character in an string in C

  - by Prab

  What's wrong with this? #include <stdio.h> void main(){ char *s="some text"; printf("%d",is_in(s,'t')); } int is_in(char *s, char c){ while(*s){ if(*s==c) return 1; s++; } return 0; } I get the following compile time error with GCC: test.c:9: error: conflicting types for ‘is_in’ test.c:9: note: an argument type that has a default promotion can’t match an empty parameter name list declaration test.c:5: note: previous implicit declaration of ‘is_in’ was here

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• Is there any way to print the actual query that mysqli->execute() makes?

  - by 0plus1

  I have a complex query that gets executed like this: if ($stmt = $dbi->prepare($pt_query)) { $stmt->bind_param('ssssssssi', $snome,$scognome,$ssocieta,$svia,$slocalita,$sprovincia,$scap,$stelefono,$sfax,$uid); $stmt->execute(); echo $dbi->error; $stmt->close(); } else { printf("Error -> %s\n", $dbi->error); } This thing is failing without any error, it simply doesn't update the database. Since there is a ton of data that gets treated before this thing I would like to know if there is any way to show the actual query that mysqli is executing in order to understand where the problem is. Thank you.

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• What is the reliable way to return error code from an MPI program?

  - by mezhaka

  The MPI standard (page 295) says: Advice to users. Whether the errorcode is returned from the executable or from the MPI process startup mechanism (e.g., mpiexec), is an aspect of quality of the MPI library but not mandatory. Indeed I had no success in running the following code: if(0 == my_rank) { FILE* parameters = fopen("parameters.txt", "r"); if(NULL == parameters) { fprintf(stderr, "Could not open parameters.txt file.\n"); printf("Could not open parameters.txt file.\n"); exit(EXIT_FAILURE); //Tried MPI_Abort() as well } fscanf(parameters, "%i %f %f %f", N, X_DIMENSION_Dp, Y_DIMENSION_Dp, HEIGHT_DIMENSION_Dp); fclose(generation_conf); } I am not able to get the error code back into the shell in order to make a decision on further actions. Neither of two error messages are printed. I think I might write the error codes and messages to a dedicated file. Has anyone ever had a similar problem and what were the options you've considered to do a reliable error reporting?

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• portable way to deal with 64/32 bit time_t

  - by MK

  I have some code which is built both on Windows and Linux. Linux at this point is always 32bit but Windows is 32 and 64bit. Windows wants to have time_t be 64 bit and Linux still has it as 32 bit. I'm fine with that, except in some places time_t values are converted to strings. So when time_T is 32 bit it should be done with %d and when it is 64bit with %lld... what is the smart way to do this? Also: any ideas how I may find all places where time_t's are passed to printf-style functions to address this issue?

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• [C] Read line from file without knowing the line length.

  - by ryyst

  Hi, I want to read in a file line by line, without knowing the line length before. Here's what I got so far: int ch = getc(file); int length = 0; char buffer[4095]; while (ch != '\n' && ch != EOF) { ch = getc(file); buffer[length] = ch; length++; } printf("Line length: %d characters.", length); I can now figure out the line length, but only for lines that are shorter than 4095 characters. Is there a better way to do this (I already used fgets() but got told it wasn't the best way)? --Ry

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• function in c language

  - by sandy101

  Hello, I am practice the function in c and come across to the program .... include int main() { float a=15.5; char ch ='C'; printit(a,ch); return 0; } printit(a,ch) { printf("%f\n%c",a,ch); } I want to know that why the above program compile and not give the error as i understood so for is ... 1) The function in c must be declared with the specific prototype (but this program does not contain the prototype ) 2)why the program give the output 'x'for the char variable 3)can the function in c are capable of accepting the value without being declared about type in parameters like what has done in the function declaration .... plz.... help

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• C++: use array of strings wrapped in namespace?

  - by John D.

  I got the following code, wishing to wrap a group of strings nicely in a namespace: namespace msgs { const int arr_sz = 3; const char *msg[arr_sz] = {"blank", "blank", "blank" }; msg[0] = "Welcome, lets start by getting a little info from you!\n"; msg[1] = "Alright, bla bla bla.."; msg[2] = "etc."; } The code inside works nicely inside a function, but I don't know how to return an array from it. The namespace idea LOOKS fine, but it returns on the last three lines: error: expected constructor, destructor, or type conversion before ‘=’ token Why can't I define the array inside a namespace, do I need to do something first? It's nice because I can call it like printf(msgs::msg[1]) etc. I want to do this I just can't wrap my head around what's wrong :(

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• malloc unable to assign memory + doesnt warn

  - by sraddhaj

  char *str=NULL; strsave(s,str,n+1); printf("%s",str-n); when I gdb debug this code I find that the str value is 0x0 which is null and also that my code is not catching this failed memory allocation , it doesnt execute str==NULL perror code ...Any idea void strsave(char *s,char *str,int n) { str=(char *)malloc(sizeof(char)* n); if(str==NULL) perror("failed to allocate memory"); while(*s) { *str++=*s++; } *str='\0'; }

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• Function argument treated as undeclared

  - by Mikulas Dite

  I've prepared this simple example which is not working for me #include <stdio.h> #include <stdlib.h> FILE *fp; char filename[] = "damy.txt"; void echo (char[] text) { fp = fopen(filename, "a"); fwrite(text, 1, strlen(text), fp); fclose(fp); printf(text); } int main () { echo("foo bar"); return 0; } It's supposed to write both to command window and to file. However, this gives compilation error - the text used in echo() is not declared. Does c need another declaration of the variable?

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• What is wrong with this c strdup code?

  - by bstullkid

  Consider this code: char *strs[] = { "string1", "string2", NULL }; char *ptr1 = NULL, *ptr2 = NULL, *tmp; short iter = 0; tmp = ptr1; while (iter < 2) { tmp = strdup(strs[iter]); tmp = ptr2; iter++; } printf("1: %s\n2: %s\n", ptr1, ptr2); I want this to output "string1\nstring2\n" however str1 and str2 remain null. What am I doing wrong?

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• this == null; surely not, but yes

  - by pm100

  I would have said that this will segfault but apparently not #include <stdio.h> class foo { public: bool thingy() {return this == 0;}; }; int main() { foo *f = 0; if(f->thingy()) printf("eating hat\n"); } I just expect that 0-xxx will never work. I assume that if we had to do some vtabling it would fail; obviously cannot access any member variables either edit; sorry - no question there. THe question is "are you surprised like me?" and it seems the answer is yes. even though nobody said yes. I got a) of course this will work b) of course this will never work c) it is undefined behavior; your mileage will vary

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• Function in xcode

  - by Joy

  I have a function which have two global variable 1.temp-a nsmutable array 2.j-a int type variable. But i cant access any global variable inside this function. I'm giving the code sample. void print( NSArray *array) { NSEnumerator *enumerator = [array objectEnumerator]; id obj; while ( nil!=(obj = [enumerator nextObject]) ) { NSString *tem=[[obj description] cString]; [temp insertObject:tem atIndex:j]; j=j+1; printf( "%s\n", [[obj description] cString]); } } Looking forward to your response. Thanks in advance..

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• MACRO Question: Returning pointer to a certain value

  - by Andrei Ciobanu

  Is it possible to write a MACRO that has a type and a value as its input parameters (MACRO(type,value)), and returns a valid pointer to a location that holds the submitted value. This macro should perform like the following function, but in a more generic manner: int *val_to_ptr(int val){ int *r = NULL; r = nm_malloc(sizeof(*r)); *r = val; return r; } Where nm_malloc() is a failsafe malloc. The Macro usage should be compatible with this usage: printf("%d",*MACRO(int,5)); Is it possible to achieve that ?

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• Reading variable with double float precision from a text file with gnuplot

  - by user3636322

  I have a text file, containing data in 3 columns like below: 0.0100000000 | 0.0058077299 | -0.0000000288 0.0110000000 | 0.0075128707 | -0.0000000373 0.0120000000 | 0.0093579693 | -0.0000000465 I want to get the variables from this file in gnuplot and use them to draw graphs: What I exactly do is like below (e.g: to pick the variable from row 2 column 3): ii= 2 a_0 = system("awk '{ if (NR == " . ii . ") printf \"%f\", $3}' " .datafile) a_0 = a_0+0. but what is written as a_0 is zero! How can I increase the precision to get the exact value?

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• argument promotions in C function calls

  - by HaoCheng

  I learned from ----As to when default promotions kick in: default argument promotions are used exactly when the expected type of the argument is unknown, which is to say when there's no prototype or when the argument is variadic. But an example confusing me is: void func(char a, char b) { printf("a=%p,b=%p\n",&a,&b); } int main(void) { char a=0x11,b=0x22; func(a,b); return 0; } It is cleard in the above example: when calling func in main, there is no need to promote the arguments a and b, but the output shows &a = &b +4 not &a = &b+1. If no promotion occured, why 4 bytes between two CHAR argument?

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• Visual Studio 2010 Compiling C code

  - by Corsen2000

  I have the following code snippet. This is a c file in visual studio 2010. If i try to compile this with the line: int hello = 10; commented out it will compile just fine. If I comment that line in it will not compile. Am I missing something or should I not be using Visual Studio 2010 to compile C code. If this is a Visual Studio problem can anyone recommend a easy to use IDE / Compiler that I can for C. Thank You int* x = (int*) calloc(1, sizeof(int)); *x = 5; //int hello = 10; printf("Hello World! %i", *x); getchar();

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• Has anyone properly interpreted HTTP request based on this demo of winpcap?

  - by httpinterpret

  The example is here, and I tried it by changing the filter to tcp and dst port 80 and the following: void packet_handler(u_char *param, const struct pcap_pkthdr *header, const u_char *pkt_data) { .... ip_len = (ih->ver_ihl & 0xf) * 4; tcp_len = (((u_char*)ih)[ip_len + 12] >> 4) * 4; tcpPayload = (u_char*)ih + ip_len + tcp_len; /* start of url - skip "GET " */ url = tcpPayload + 4; end_url = strchr((char*)url, ' '); url_length = end_url - url; final_url = (u_char*)malloc(url_length + 1); strncpy((char*)final_url, (char*)url, url_length); final_url[url_length] = '\0'; printf("%s\n", final_url); .... } But through debug, I see tcpPayload is full of messy code,not supposed "GET ..." stuff. What's wrong with my implement?

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• Using Classes / OOP in PHP

  - by Alex Demchak

  I'm pretty proficient with PHP, outside of OOP - which I am just now starting to jump in to. I've been watching videos and reading tutorials, but they are all still pretty confusing... If I have FILE 1 (class.time.php) class Time { function GetTime(){ $time = date('H:i:s'); printf($time); } } and then in a nother php page I've got FILE 2 (page.php) I can do include('class.time.php'); and then anywhere in this page I can then do $time = new Time; //Calling the class and setting the class to a variable $time->GetTime(); //This is BASICALLY saying (run the 'GetTime' function in the 'Time Class' My main question is, is the comment above (This is BASICALLY saying.....) correct? or is there a better way to think of it?

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• Why does this C program compile?

  - by AdmiralJonB

  I've just come across someone's C code that I'm confused as to why it is compiling. There are two points I don't understand. First, the function prototype has no parameters compared to the actual function definition. Secondly, the parameter in the function definition doesn't have an type. #include <stdio.h> int func(); int func(param) { return param; } int main() { int bla = func(10); printf("%d",bla); } Could someone please explain to me why this works? I've tested it in a couple of compilers and it works fine.

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• C: stdin and std* errs

  - by user355926

  I want to my manipulate Stdin, then Std* but some errs: $ gcc testFd.c testFd.c:9: error: initializer element is not constant testFd.c:9: warning: data definition has no type or storage class testFd.c:10: error: redefinition of `fd' testFd.c:9: error: `fd' previously defined here testFd.c:10: error: `mode' undeclared here (not in a function) testFd.c:10: error: initializer element is not constant testFd.c:10: warning: data definition has no type or storage class testFd.c:12: error: syntax error before string constant $ cat testFd.c #include <stdio.h> #include <sys/ioctl.h> int STDIN_FILENO = 1; // I want to access typed // Shell commands, dunno about the value: unsigned long F_DUPFD; fd = fcntl(STDIN_FILENO, F_DUPFD, 0); fd = open("/dev/fd/0", mode); printf("STDIN = %s", fd);

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• dreferencing 2 d array

  - by ashish-sangwan

  Please look at this peice of code :- #include<stdio.h> int main() { int arr[2][2]={1,2,3,4}; printf("%d %u %u",**arr,*arr,arr); return 0; } When i compiled and executed this program i got same value for arr and *arr which is the starting address of the 2 d array. For example:- 1 3214506 3214506 My question is why does dereferencing arr ( *arr ) does not print the value stored at the address contained in arr ?

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• Extract data from uint8 to double

  - by HADJ AMOR HASSEN

  I have a C function receiving a uint8 pointer with another parameter which is its size (number of bytes). I want to extract double data from this buffer. Here is my code: Write(uint8* data, uint8 size) /* data and size are given by a callback to my function)*/ { double d; for (i = 0; i < size; i++) { d = ((double*)&data)[i]; printf(" d = %d\n"); } } The problem is that I am not receiving what I am sending within an external hardware. I guess that my cast is wrong. I tried other methods but without any good result. I am still not able to get what I send.

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