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Ye olde C

May 13, 2025LeifMessinger
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socketUDPServer.c

Aug 5, 2023LeifMessinger

0 likes • 3 views

// Server 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 RECIEVE_BUFFER_SIZE 1024
const char* responseMessage = "Hello from server";
// Driver code
int main() {
//Create a UDP socket
//int socket(int domain, int type, int protocol);
//Domain is the place where the data goes. AF_BLUETOOTH, AF_INET6, AF_UNIX is local communication between different programs
//Type is the type of connection, so connection based (TCP), connectionless (UDP) or somewhere in between or beyond
//Protocol is an enum or flags that give some more options specific to that type. For SOCK_STREAM, you can force it to use SCTP instead of TCP. For SOCK_RAW, it can give you control over the ip frame, and even the ethernet frame.
//So this function makes a file descriptor to an IPV4 UDP 'connection' with no options.
int sockfd = socket(AF_INET, SOCK_DGRAM, 0);
// Creating socket file descriptor
if ( sockfd < 0) {
perror("socket creation failed");
exit(EXIT_FAILURE);
}
struct sockaddr_in serverAddress;
memset(&serverAddress, 0, sizeof(serverAddress));
// Filling server information
serverAddress.sin_family = AF_INET; // IPv4
serverAddress.sin_addr.s_addr = INADDR_ANY;
serverAddress.sin_port = htons(PORT);
// Bind the socket with the server address
if(bind(sockfd, (const struct sockaddr*)&serverAddress, sizeof(serverAddress))){ //Bind returns 0 if succeeded, or -1 if failed. -1 is still true.
perror("bind failed");
exit(EXIT_FAILURE);
}
struct sockaddr_in clientAddress; unsigned int clientAddressSize = sizeof(clientAddress);
memset(&clientAddress, 0, clientAddressSize);
char buffer[RECIEVE_BUFFER_SIZE];
int bytesRecieved = recvfrom(sockfd, (char*)buffer, RECIEVE_BUFFER_SIZE, MSG_WAITALL, (struct sockaddr*) &clientAddress, &clientAddressSize); //sets clientAddress to the client's address and the new size
buffer[bytesRecieved] = '\0';
printf("Client : %s\n", buffer);
sendto(sockfd, (const char*)responseMessage, strlen(responseMessage), MSG_CONFIRM, (const struct sockaddr*) &clientAddress, clientAddressSize);
printf("Hello message sent.\n");
return 0;
}

fork() example

Nov 19, 2022CodeCatch

0 likes • 2 views

#include <stdio.h>
#include <sys/types.h>
#include <unistd.h>
int main() {
pid_t pid; /* could be int */
int i;
pid = fork();
printf("PID=%d\n", pid);
if (pid > 0) {
/* parent */
for (i = 0; i < 10; i++)
printf("\t\t\tPARENT %d\n", i);
} else {
/* child */
for (i = 0; i < 10; i++)
printf("CHILD %d\n", i);
}
return 0;
}

socketTCPServer.c

Aug 5, 2023LeifMessinger

0 likes • 0 views

// compile: gcc socketTCPServer.c -o socketTCPServer.out
// usage : ./socketTCPServer.out port
// Server
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <string.h>
#include <sys/types.h>
int main(int argc, char *argv[]){
int listenfd = 0, connfd = 0, cli_size, portno;
struct sockaddr_in serv_addr, cli_addr;
char sendBuff[1025];
if((listenfd = socket(AF_INET, SOCK_STREAM, 0)) == -1){
printf("socket error\n");
exit(EXIT_FAILURE);
}
memset(&serv_addr, '0', sizeof(serv_addr));
memset(sendBuff, '0', sizeof(sendBuff));
serv_addr.sin_family = AF_INET;
serv_addr.sin_addr.s_addr = htonl(INADDR_ANY);
portno = atoi(argv[1]);
serv_addr.sin_port = htons(portno);
const int on = 1;
setsockopt(listenfd, SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on));
if(bind(listenfd, (struct sockaddr*)&serv_addr, sizeof(serv_addr)) == -1){
printf("bind error\n");
exit(EXIT_FAILURE);
}
if(listen(listenfd, 5) == -1){
printf("listen error\n");
exit(EXIT_FAILURE);
}
while(1){
cli_size = sizeof(cli_addr);
if((connfd = accept(listenfd, (struct sockaddr*)&cli_addr, &cli_size)) == -1){
printf("accept error\n");
exit(EXIT_FAILURE);
}
strcpy(sendBuff, "Server Message: SUCCESS\n");
write(connfd, sendBuff, strlen(sendBuff));
close(connfd);
sleep(1);
}
return 0;
}

socketUDPPingServer.c

Aug 5, 2023LeifMessinger

0 likes • 2 views

// Server 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 RECIEVE_BUFFER_SIZE 1024
// Driver code
int main() {
//Create a UDP socket
//int socket(int domain, int type, int protocol);
//Domain is the place where the data goes. AF_BLUETOOTH, AF_INET6, AF_UNIX is local communication between different programs
//Type is the type of connection, so connection based (TCP), connectionless (UDP) or somewhere in between or beyond
//Protocol is an enum or flags that give some more options specific to that type. For SOCK_STREAM, you can force it to use SCTP instead of TCP. For SOCK_RAW, it can give you control over the ip frame, and even the ethernet frame.
//So this function makes a file descriptor to an IPV4 UDP 'connection' with no options.
int sockfd = socket(AF_INET, SOCK_DGRAM, 0);
// Creating socket file descriptor
if ( sockfd < 0) {
perror("socket creation failed");
exit(EXIT_FAILURE);
}
struct sockaddr_in serverAddress;
memset(&serverAddress, 0, sizeof(serverAddress));
// Filling server information
serverAddress.sin_family = AF_INET; // IPv4
serverAddress.sin_addr.s_addr = INADDR_ANY;
serverAddress.sin_port = htons(PORT);
// Bind the socket with the server address
if(bind(sockfd, (const struct sockaddr*)&serverAddress, sizeof(serverAddress))){ //Bind returns 0 if succeeded, or -1 if failed. -1 is still true.
perror("bind failed");
exit(EXIT_FAILURE);
}
struct sockaddr_in clientAddress; unsigned int clientAddressSize = sizeof(clientAddress);
memset(&clientAddress, 0, clientAddressSize);
char buffer[RECIEVE_BUFFER_SIZE];
while(1){
int bytesRecieved = recvfrom(sockfd, (char*)buffer, RECIEVE_BUFFER_SIZE, MSG_WAITALL, (struct sockaddr*) &clientAddress, &clientAddressSize); //sets clientAddress to the client's address and the new size
buffer[bytesRecieved] = '\0';
//printf("Client : %s\n", buffer);
//The client might be like PINGUIN or something, but this is to ensure PING\n\r also gets accepted
if(bytesRecieved >= 4 && (strncmp("PING", buffer, 4) == 0)){
const char* responseMessage = "PONG";
sendto(sockfd, (const char*)responseMessage, strlen(responseMessage), MSG_CONFIRM, (const struct sockaddr*) &clientAddress, clientAddressSize);
//printf("Hello message sent.\n");
}else{
printf("Server bytes recieved: %d\nServer message recieved: %s", bytesRecieved, buffer);
}
}
return 0;
}

execlp() example

Nov 19, 2022CodeCatch

0 likes • 0 views

#include <stdio.h>
#include <unistd.h>
int main() {
char * cmd[] = {
"who",
"ls",
"date"
};
int i;
printf("0=who 1=ls 2=date : ");
scanf("%d", & i);
execlp(cmd[i], cmd[i], (char * ) 0);
printf("execlp failed\n");
return 0;
}

signal() example

Nov 19, 2022CodeCatch

0 likes • 0 views

#include <stdio.h>
#include <assert.h>
#include <signal.h>
void myHandler(int iSig) {
printf("In myHandler with argument %d\n", iSig);
}
int main() {
void( * pfRet)(int) = signal(SIGINT, myHandler);
assert(pfRet != SIG_ERR);
printf("Entering an infinite loop\n");
while (1) {
printf(".");
}
return 0; // use CTRL+\ to exit
}