why when I declare an int variable my aplication freezes? C program - c

Question

this is my code for the server so far:
a function that finds if a word is in a file:
int Search_in_File_name(char *fname, char *str) {
FILE *fp;
int line_num = 1;
int find_result = 0;
char temp[512];
if((fp = fopen(fname, "r")) == NULL) {
return(-1);
}
while(fgets(temp, 512, fp) != NULL) {
if((strstr(temp, str)) != NULL) {
//printf("\n[copil] logare reusita");
find_result++;
}
line_num++;
}
if(find_result == 0) {
//printf("\nnume incorect");
fclose(fp);
return(3);
}
//Close the file if still open.
if(fp) {
fclose(fp);
}
return(4);
}
and main where i have to look see if a client logs in before doing something else. I used fork for every client that connects to the server. I want to create a file in my project directory for every client and i need the number of the client to do that( or the port specified by "ntohs(newAddr.sin_port)" but i can't obtain the number of the client because i can't declare any int variables.
int main(){
int sockfd, ret;
struct sockaddr_in serverAddr;
int newSocket;
struct sockaddr_in newAddr;
socklen_t addr_size;
char buffer[1024];
pid_t childpid;
sockfd = socket(AF_INET, SOCK_STREAM, 0);
if(sockfd < 0){
printf("[-]Error in connection.\n");
exit(1);
}
printf("[+]Server Socket is created.\n");
memset(&serverAddr, '\0', sizeof(serverAddr));
serverAddr.sin_family = AF_INET;
serverAddr.sin_port = htons(PORT);
serverAddr.sin_addr.s_addr = inet_addr("127.0.0.1");
ret = bind(sockfd, (struct sockaddr*)&serverAddr, sizeof(serverAddr)); //asociaza adresa serverAddr(localhost) la socketul creat (sockfd)
if(ret < 0){
printf("[-]Error in binding.\n");
exit(1);
}
printf("[+]Bind to port %d\n", PORT);
if(listen(sockfd, 10) == 0){ //marcheaza socketul (sockfd) ca fiind socketul care va accepta o conexiune viitoare si limita maxima de conexiuni in asteptare
printf("[+]Listening....\n");
}else{
printf("[-]Error in binding.\n");
}
while(1){
newSocket = accept(sockfd, (struct sockaddr*)&newAddr, &addr_size); //ia prima conexiune din lista asociata lui sockfd prin listen si creaza un nou socket si returneaza un descriptor de fisier pentru acel nou socket
if(newSocket < 0){
exit(1);
}
printf("Connection accepted from %s:%d\n", inet_ntoa(newAddr.sin_addr), ntohs(newAddr.sin_port));
int i=0;
if((childpid = fork()) == 0){
close(sockfd);
int ok=0;
char* nume_fisier;
while(1){
recv(newSocket, buffer, 1024, 0);
if(strcmp(buffer, ":exit") == 0){
printf("Disconnected from %s:%d\n", inet_ntoa(newAddr.sin_addr), ntohs(newAddr.sin_port));
break;
}else if(strncmp(c1, buffer, strlen(c1))==0 && ok ==0){
int lungCom, lungNume;
char name[lungNume];
lungCom=strlen(buffer); //lungimea comenzii
lungNume=lungCom-strlen(c1); //lungimea numelui
name[lungNume]='\0';
strncpy(name,&buffer[lungCom-lungNume],lungNume);//pun numele din comanda in variabia name
printf("\n[copil] asta e numele: %s ", name);
printf("\n[copil] %s", w1);
if(Search_in_File_name("nume.txt", name)==4){// daca am gasit numele in lista
i=i+1;
printf("----%d----",i);
send(newSocket, v1, strlen(v1), 0);
bzero(buffer, sizeof(buffer));
ok=1;
printf("\n[copil] am trimis mesajul: %s \n", v1);
}else{ // daca nu am gasit numele in lista
send(newSocket, v2, strlen(v2), 0);
printf("\n[copil] am trimis mesajul: %s \n", v2);
bzero(buffer, sizeof(buffer));
}
}else if(strcmp(buffer, "logout")==0 && ok == 1){
printf("incercare delogare de la %s:%d\n", inet_ntoa(newAddr.sin_addr), ntohs(newAddr.sin_port));
printf("delogat de la %s:%d\n", inet_ntoa(newAddr.sin_addr), ntohs(newAddr.sin_port));
ok=0;
printf("Client: %s\n", buffer);
send(newSocket, d1, strlen(d1), 0);
bzero(buffer, sizeof(buffer));
}else if(strcmp(buffer, "logout")==0 && ok == 0){
printf("incercare delogare de la %s:%d\n", inet_ntoa(newAddr.sin_addr), ntohs(newAddr.sin_port));
printf("Client: %s\n", buffer);
send(newSocket, d2, strlen(d2), 0);
bzero(buffer, sizeof(buffer));
}else if(strcmp(buffer, "cos")==0 && ok == 1){
printf("incercare creare cos de la %s:%d\n", inet_ntoa(newAddr.sin_addr), ntohs(newAddr.sin_port));
printf("Client: %s\n", buffer);
printf("----%d---:", ntohs(newAddr.sin_port));
//nume_fisier=creare_cos_client(nume_client);
//printf("---nume_fisier: %s", nume_fisier);
send(newSocket, cos1, strlen(cos1), 0);
bzero(buffer, sizeof(buffer));
}else{
printf("Client: %s\n", buffer);
send(newSocket, buffer, strlen(buffer), 0);
bzero(buffer, sizeof(buffer));
}
}
}
}
close(newSocket);
return 0;
}
If i delete that "int i=0; " before the fork my program works fine but as soon as i add it back(anywhere) the client can't take any input and the server doesn't check if the name is in the file or not.

Answer 1

recv(newSocket, buffer, 1024, 0);
if(strcmp(buffer, ":exit") == 0){
Two mistakes here:
You ignore the return value of recv. So you have no idea how many bytes you received. How can you do anything useful with some data if you have no idea how much data you have?
You can only pass a C-style string to strcmp. At this point, buffer only contains the raw data you received from the other side. It isn't a C-style string because, by definition, a C-style string has a terminating zero byte.
You have another more fundamental problem though -- your use of strcmp suggests you think you are using a message protocol and have received a message. But you are using TCP and TCP is not a message protocol.
It's hard to say precisely why adding int i =0; saves you from crashing or freezing. But my guess is that the zero just happens to be stored in memory after the buffer and so, by luck, provides the terminating zero byte that strcmp requires. But that's just a guess.