c syntax: array
For char[size], is it true that size must be constant? Or say,will it work ? int length; ... char[length] arr; Sorry,don't have the environment here so can't try it myself. ...
c
lvalue required
what does the error message "Lvalue required" actually mean? ...
what is the usefulness of creating our own header file
Possible Duplicate: What are the point of header files in C? what is the usefulness in creating our own header file while doing a project?? ...
C programming language, increment-decrement operators.
#include<stdio.h> #include<conio.h> main() { int i=5; printf("%d",--i - ++i);//give output=0 printf("%d",++i + ++i);//give output=14 printf("%d",i++ + ++i);// give output=12 printf("%d",--i + ++i);// give output=10 printf("%d",i+++++i); // error : invalid lvalue in increment /* in this case tell me how parsing of expression i+++++i ...
Reproducing "Gallery of processor cache effects"
Having read this article I tried to reproduce the example on my Mac. However my curve for the first example looks completely different and I don't understand why.. My code is below: #include <mach/mach_time.h> #include <time.h> #include <stdio.h> #include <stdlib.h> void mach_absolute_difference(uint64_t end, uint64_t start, struct ...
C exit function not doing what I thought it would
When I use a debugger I can tell the exit is not exiting the function. Am I using the exit function wrong? (i must be) how do I fix this? int is_prime(int x,char array[]){ int divider = (x-1); float test; while(x>-1){ test = isdigit((x % divider)); //isdigit returns !0 if digit if(divider == '1'){ return(1); //if divi...
modified a constant again.. with void pointers
Possible Duplicate: Modified a constant in c const int z = 420; const void *v; v = &z; printf("\n%d | %d",z,*(int *)v); //420 | 420 printf("\n%d | %d",*(char *)&z,*(char *)v); //0th-Bit same value //-92 | -92 printf("\n%d | %d",*((char *)&z+1),*((char *)v+1) ); //1st-Bit same value //1 | 1 /*************************...
What is the rationale behind typedef vs struct/union/enum, couldn't there be only one namespace?
In C if I declare a struct/union/enum: struct Foo { int i ... } when I want to use my structure I need to specify the tag: struct Foo foo; To loose this requirement, I have to alias my structure using typedef: typedef struct Foo Foo; Why not have all types/structs/whatever in the same "namespace" by default? What is the rati...
Algorithm for generating normally distributed random values in C?
Possible Duplicate: Converting a Uniform Distribution to a Normal Distribution Hello. I'd like to know of any algorithm implemented in C which can take a random value between 0 and 1, the mean and standard deviation and then return a normally distributed result. I have too little brainpower to figure this out for myself righ...
"--" operator in while ( ) loop
I am reading K&R book, on page 63 there is a line while (--lim > 0 && (c=getchar()) != EOF && c != '\n') where lim is int equal to 1000 My question, why is lim is not decreasing after consequential runs of while loop ? As I see it, --lim is equivalent to "lim = lim - 1" ===============================================================...
What is the exact meaning of "int const* " in C?
Possible Duplicates: const int = int const ? Const in C hi, I would like to know the exact meaning of "int const* " in C ,And also a small comparison between "const int*" and "int const*" in an embedded programming system. __kanu ...
Simplifying compilation with each of a list of options
I've got a list of definitions: MASTER, SLAVE0, SLAVE1, ... SLAVE9 to control which array of audio data is programmed into a microcontroller. The micro can hold no more than one sound file, so I have included the following definitions at the top of my main.c file: #define MASTER #define SLAVE0 #define SLAVE1 .... #define SLAVE9 Then...
How to append different files and extract them for verification in my code?
if i have both encrypted message and signature (let's say two different size files), i just want to append them and store in a file together but later i will use the same "only one file" to extract the files and verify in my code. in that way my code will get only one file as an input but can understand which is encrypted file and signa...
How to display the maximum value of a unsigned long long in C?
What am I doing wrong here? $ cat size.c #include<stdio.h> #include<math.h> int main() { printf ("sizeof unsigned int = %d bytes.\n", sizeof(unsigned int)); printf ("sizeof unsigned long long = %d bytes.\n", sizeof(unsigned long long)); printf ("max unsigned int = %d\n", (int)(pow(2, 32) - 1)); printf ("max unsigned long long = %lld\...
How are numbers greater than 2^32 handled by a 32 bit machine?
I am trying to understand how calculations involving numbers greater than 232 happen on a 32 bit machine. C code $ cat size.c #include<stdio.h> #include<math.h> int main() { printf ("max unsigned long long = %llu\n", (unsigned long long)(pow(2, 64) - 1)); } $ gcc output $ gcc size.c -o size $ ./size max unsigned long long ...
main(int argc, char *argv[])
Possible Duplicates: What are the arguments to main() for? What does int argc, char *argv[] mean? Every program is starts with main(int argc, char *argv[]) definition . I don't understand what does it mean?I would be very glad if somebody could explain why we use these arguments if we dont use them in the program? Why not j...
How does this code calculate the number of CPU cycles elapsed?
Taken from this SO thread, this piece of code calculates the number of CPU cycles elapsed running code between lines //1 and //2. $ cat cyc.c #include<stdio.h> static __inline__ unsigned long long rdtsc(void) { unsigned long long int x; __asm__ volatile (".byte 0x0f, 0x31" : "=A" (x)); return x; } int main() { unsigne...
Can you help improve one of my college's class on low level software and peripheral interfaces?
Hello, everyone. I am a 2nd year student at the Portuguese Engineering Faculty at the University of Oporto. I am currently studying for a Joint Degree (5 yr undergrad + masters) in Informatics and Computer engineering (which is basically software engineering :P). I think the course is great, and well structured, but I was in for a nast...
Can I walk through my process' page table in userspace?
Hello, Can anyone suggest some learning materials to accomplish my question? I'm working with the Linux kernel. I'm planning on conducting an experiment, but need access to my process' page table, and so far have only found kernel space code to accomplish what I want. Thanks ...
Labels in GCC inline assembly
In my ongoing experimentation with GCC inline assembly, I've run into a new problem regarding labels and inlined code. Consider the following simple jump: __asm__ ( "jmp out;" "out:;" : : ); This does nothing except jump to the out label. As is, this code compiles fine. But if you place it inside a function, and the...