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fork() example

Nov 19, 2022CodeCatch
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Ye olde C

May 13, 2025LeifMessinger

0 likes • 2 views

#include <stdio.h>
#include <stdlib.h>
calculate(a, b)
int a;
int b;
{
printf("%d", a+b);
}
main(argc, argv)
int argc;
char** argv;
{
if(argc < 3){
return 0;
}
calculate(atoi(argv[1]), atoi(argv[2]));
}

Fast inverse square root

Nov 19, 2022CodeCatch

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// The following code is the fast inverse square root implementation from Quake III Arena
// this code has been stripped of C preprocessor directives, but includes the exact original comment text
float Q_rsqrt( float number )
{
long i;
float x2, y;
const float threehalfs = 1.5F;
x2 = number * 0.5F;
y = number;
i = * ( long * ) &y; // evil floating point bit level hacking
i = 0x5f3759df - ( i >> 1 ); // what the fuck?
y = * ( float * ) &i;
y = y * ( threehalfs - ( x2 * y * y ) ); // 1st iteration
// y = y * ( threehalfs - ( x2 * y * y ) ); // 2nd iteration, this can be removed
return y;
}

pipe() example

Nov 19, 2022CodeCatch

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#include <stdio.h>
#include <string.h>
#include <unistd.h>
#define READ 0 /* The index of the read end of the pipe */
#define WRITE 1 /* The index of the write end of the pipe */
char * phrase = "This goes in the pipe";
int main() {
int fd[2], bytesRead;
char message[100]; /* Parent process' message buffer */
pipe(fd); /* Create unnamed pipe */
if (fork() == 0) /* Child, writer */ {
close(fd[READ]); /* Close unused end */
write(fd[WRITE], phrase, strlen(phrase) + 1); /* Include NULL */
close(fd[WRITE]); /* Close used end */
} else /* Parent, reader */ {
close(fd[WRITE]); /* Close unused end */
bytesRead = read(fd[READ], message, 100);
printf("Parent just read %i bytes: %s\n", bytesRead, message);
close(fd[READ]); /* Close used end */
}
}

Heavy Coin

Oct 4, 2023AustinLeath

0 likes • 3 views

#include <stdio.h>
#include <stdlib.h>
// give an array of identical coins (ints), represented by 1's and one 2
// we can find the heavy coin (2) by summing the contents of the thirds
int sum_subarr(int arr[], int l, int r){
int sum = 0;
for(int i = l; i <= r; i++)
{
sum += arr[i];
}
return sum;
}
int heavy_coin(int arr[], int l, int r){
if(r == l)
{
return r;
}
int midl = l + (r - l)/3;
int midr = r - (r - l)/3;
int lw = sum_subarr(arr, l, midl);
int mw = sum_subarr(arr, midl + 1, midr);
if ( lw > mw )
{
return heavy_coin(arr, l, midl);
}
else if ( lw < mw )
{
return heavy_coin(arr, midl + 1, midr);
}
else
{
return heavy_coin(arr, midr + 1, r);
}
}
int main(int argc, char *argv[])
{
int arr[] = {1,1,1,1,2,1,1,1,1};
int l = 0;
int r = 8;
int res = -1;
res = heavy_coin(arr, l, r);
printf("Hevy coin is at index: %d\n", res);
return EXIT_SUCCESS;
}

Bitwise operators with pointers

Nov 18, 2022AustinLeath

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#include <stdio.h>
#include <stdlib.h>
int main(){
int * int_ptr;
int_ptr = (int *)malloc(2*sizeof(int));
if(!int_ptr) {
printf("Something went wrong while allocating memory. Exiting...");
exit(1);
}
printf("Enter first integer: ");
scanf("%i", &int_ptr[0]);
printf("Enter second integer: ");
scanf("%i", &int_ptr[1]);
printf("Original values: 1st = %i 2nd = %i\n",int_ptr[0], int_ptr[1]);
int_ptr[0] = int_ptr[0] ^ int_ptr[1];
//printf("%i\n", int_ptr[0]);
int_ptr[1] = int_ptr[0] ^ int_ptr[1];
//printf("%i\n", int_ptr[1]);
int_ptr[0] = int_ptr[0] ^ int_ptr[1];
//printf("%i\n", int_ptr[0]);
printf("Swapped values: 1st = %i 2nd = %i\n", int_ptr[0], int_ptr[1]);
free(int_ptr);
exit(0);
}

socketUDPPingClient.c

Aug 5, 2023LeifMessinger

0 likes • 3 views

// Client side implementation of UDP client-server model
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <netinet/in.h>
#define PORT 8008
#define MAXLINE 1024
// Driver code
int main() {
char buffer[MAXLINE];
struct sockaddr_in servaddr;
// Creating socket file descriptor
int sockfd = socket(AF_INET, SOCK_DGRAM, 0);
if ( sockfd < 0 ) {
perror("socket creation failed");
exit(EXIT_FAILURE);
}
struct timeval timeout;
timeout.tv_sec = 1; //Wait 1 second
timeout.tv_usec = 0;
if (setsockopt (sockfd, SOL_SOCKET, SO_RCVTIMEO, &timeout, sizeof timeout) < 0) perror("setsockopt failed\n");
if (setsockopt (sockfd, SOL_SOCKET, SO_SNDTIMEO, &timeout, sizeof timeout) < 0) perror("setsockopt failed\n");
memset(&servaddr, 0, sizeof(servaddr));
// Filling server information
servaddr.sin_family = AF_INET;
servaddr.sin_port = htons(PORT);
servaddr.sin_addr.s_addr = inet_addr("192.168.4.65");
for(int i = 0; i < 10; ++i){
char* message = "PING";
int sendStatus = sendto(sockfd, (const char *)message, strlen(message), MSG_CONFIRM, (const struct sockaddr *) &servaddr, sizeof(servaddr));
if(sendStatus >= 0){
printf("Sent PING\n");
}else{
printf("Send failed\n");
continue;
}
int len = sizeof(struct sockaddr_in);
int bytesRecieved = recvfrom(sockfd, (char *)buffer, MAXLINE, MSG_WAITALL, (struct sockaddr *) &servaddr, &len); //We can reuse servaddr because the port the server sends messages from is the same one we send to
if(bytesRecieved >= 0){
buffer[bytesRecieved] = '\0';
printf("Recieved %s\n", buffer);
}else{
printf("Recieved nothing: Packet Dropped\n", buffer);
}
}
close(sockfd);
return 0;
}