C Programming Notes

C Basics

Basics

& gives the address of an object * dereferencing operation - gets object pointer points to

alloc(n)

returns pointer to n consecutive character positions

afree(p)

releases storage - must be made in opposite order to the calls made on alloc

malloc

free

NODE STRUCTURE

struct type_node {

void * data; struct type_node * prev; struct type_node * next;

};

main() {

struct type_node * head; return 0;

}

//allocate space for a structure struct type_node * pNode; pNode = talloc(); //talloc routine returns pointer

//to a free space to hold the node

IO

getline adds ‘0’ at end of array it reads so “hellon” is stored as [h][e][l][l][o][n][0]

Register declaration

Register declaration

f(register unsigned m, register long n) {

register int i;

}

Macro Subsitution

Macro Substitution

#define name replacement text #define forever for (;;) /* infinite loop */

Socket Programming

Big-endian bytes are in a normal order Little-endian bytes are backwards

Convert numbers to Network Byte Order before they go out the wire

htons() Host to Network Short htonl() host to network long

Convert them to Host Byte Order as they come in off the wire ntohs() network to host short ntohl() network to host long

struct addrinfo {

int ai_flags; // AI_PASSIVE, AI_CANONNAME, etc. int ai_family; // AF_INET, AF_INET6, AF_UNSPEC int ai_socktype; // SOCK_STREAM, SOCK_DGRAM int ai_protocol; // use 0 for “any” size_t ai_addrlen; // size of ai_addr in bytes struct sockaddr *ai_addr; // struct sockaddr_in or _in6 char *ai_canonname; // full canonical hostname

struct addrinfo *ai_next; // linked list, next node

};

struct sockaddr {

unsigned short sa_family; // address family, AF_xxx char sa_data[14]; // 14 bytes of protocol address

};

// (IPv4 only–see struct sockaddr_in6 for IPv6) struct sockaddr_in {

short int sin_family; // Address family, AF_INET unsigned short int sin_port; // Port number struct in_addr sin_addr; // Internet address unsigned char sin_zero[8]; // Same size as struct sockaddr

};

// (IPv4 only–see struct in6_addr for IPv6) // Internet address (a structure for historical reasons) struct in_addr {

uint32_t s_addr; // that’s a 32-bit int (4 bytes)

};

inet_ntop() network to presentation

// IPv4: char ip4[INET_ADDRSTRLEN]; // space to hold the IPv4 string struct sockaddr_in sa; // pretend this is loaded with something

inet_ntop(AF_INET, &(sa.sin_addr), ip4, INET_ADDRSTRLEN); printf(“The IPv4 address is: %sn”, ip4);

// IPv6: char ip6[INET6_ADDRSTRLEN]; // space to hold the IPv6 string struct sockaddr_in6 sa6; // pretend this is loaded with something inet_ntop(AF_INET6, &(sa6.sin6_addr), ip6, INET6_ADDRSTRLEN); printf(“The address is: %sn”, ip6);

#include <sys/types.h> #include <sys/socket.h> #include <netdb.h> int getaddrinfo(const char *node, // e.g. “www.example.com” or IP

const char *service, // e.g. “http” or port number const struct addrinfo *hints, struct addrinfo **res);

int status; struct addrinfo hints; struct addrinfo *servinfo; // will point to the results

memset(&hints, 0, sizeof hints); // make sure the struct is empty hints.ai_family = AF_UNSPEC; // don’t care IPv4 or IPv6 hints.ai_socktype = SOCK_STREAM; // TCP stream sockets hints.ai_flags = AI_PASSIVE; // fill in my IP for me

if ((status = getaddrinfo(NULL, “3490”, &hints, &servinfo)) != 0) {

fprintf(stderr, “getaddrinfo error: %sn”, gai_strerror(status)); exit(1);

}

// servinfo now points to a linked list of 1 or more struct addrinfos // ... do everything until you don’t need servinfo anymore .... freeaddrinfo(servinfo); // free the linked-list