[Linux] 시스템프로그래밍 기본

Open()

#include <fcntl.h>
#include <stdio.h>
main()
{
 char* fname = "test.txt";
 int fd;
  
 fd = open(fname, O_RDONLY);
 if(fd<0)
  perror("open()");
 else
 {
  printf("Success!\nFilename : %10s\nDescriptor : %d\n", fname,fd);
  close(fd);
 }
}

 

Read()

#include <stdio.h>
#include <string.h>
#include <fcntl.h>
#include <unistd.h>
#include <stdlib.h>
main()
{
 char *fname = "test.txt";
 int fd1, fd2, cnt;
 char buf[30];
 
 fd1 = open(fname, O_RDONLY);
 fd2 = open(fname, O_RDONLY);
 if(fd1 <0 || fd2 <0 )
 {
  perror("open error");
  exit(-1);
 }
 
 cnt = read(fd1, buf, 12);
 buf[cnt] = '\0';
 printf("fd1's first printf : %s\n", buf);
 lseek(fd1,1,SEEK_CUR);
 
 cnt = read(fd1,buf,12);
 buf[cnt] = '\0';
 printf("fd1's second printf: %s\n", buf);
 cnt = read(fd2, buf, 12);
 buf[cnt] = '\0';
 
 printf("fd2's first printf : %s\n", buf);
 lseek(fd2,1,SEEK_CUR);
 cnt = read(fd2, buf, 12);
 buf[cnt] = '\0';
 
 printf("fd2's second printf: %s\n", buf);
 
 exit(0);
}

lseek()

#include <sys/types.h>
#include <fcntl.h>
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
main()
{
 char* fname = "test.txt";
 int fd;
 off_t fsize;
  
 if((fd=open(fname, O_RDONLY)) <0 )
 {
  perror("open()");
  exit(-1);
 }
 fsize = lseek(fd, 0, SEEK_END);
 printf("The size of <%s> is %lu bytes.\n", fname,fsize);
 exit(0);
}

exec()

#include <sys/types.h>
#include <sys/wait.h>
#include <stdlib.h>
#include <unistd.h>
#include <fcntl.h>
char *env_init[] = { "USER = unknown", "PATH=/tmp", NULL };

int main()
{
 pid_t pid;
 if((pid = fork()) <0)
  perror("fork error");
 else if (pid==0)
 {
  if(execle("./echoall", "echoall", "myarg1", "My ARG2", (char*)0, env_init) <0 )
   perror("execle error");
 }
 if(waitpid(pid,NULL,0)<0)
  perror("wait error");
 
 if((pid = fork()) <0)
  perror("fork error");
 else if(pid ==0)
 {
  if(execlp("./echoall", "echoall", "only 1 arg", (char*)0)<0)
   perror("execlp error");
 }
 exit(0);
}

fflush()

#include <stdio.h>

int main()
{
 char* prompt = "Prompt>>";
 char command[80];
 
 for(;;)
 {
  fputs(prompt, stdout);
  if(fgets(command, sizeof(command), stdin) == NULL)
   break;
  system(command);
 }
 fprintf(stdout, "Good Bye ...");
 fflush(stdout);
 system("clear");
 
 return 0;
}

 

fork()

#include <sys/types.h>
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h>

static int glob = 6;
char buf[] = "a write to stdout\n";

int main()
{
 int var;
 pid_t pid;
 
 var = 88;
 if(write(STDOUT_FILENO, buf, sizeof(buf)-1) != sizeof(buf)-1)
  perror("write error");
 printf("before fork\n");
 
 if((pid = fork())<0)
  perror("fork error");
 else if(pid==0)
 {
  glob++;
  var++;
 }
 else
  sleep(2);
 
 printf("pid = %d, glob =%d, var = %d\n", getpid(), glob, var);
 exit(0);
}

vfork()

#include <sys/types.h>
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h>

static int glob = 6;

int main()
{
 int var;
 pid_t pid;
 
 var = 88;

 printf("before vfork\n");
 
 if((pid = vfork())<0)
  perror("fork error");
 else if(pid==0)
 {
  glob++;
  var++;
  printf("pid = %d, glob =%d, var = %d\n", getpid(), glob, var);
  _exit(0);
 }
 else
  sleep(2);
 
 printf("pid = %d, glob =%d, var = %d\n", getpid(), glob, var);
 exit(0);
}

chdir()

#include <unistd.h>
#include <stdio.h>

#define PATH_MAX 1024

int main(void)
{
 char path[PATH_MAX+1];
 if(chdir("/tmp") <0)
  perror("error chdir");
 else
 {
  if(getcwd(path, PATH_MAX) == NULL)
   perror("error getcwd");
  else
   printf("Current woring directory changed to %s \n", path);
 }

 return 0;
}

utime()

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
#include <fcntl.h>
#include <utime.h>
#include <sys/stat.h>

int main(int argc, char* argv[])
{
 int i;
 struct stat statbuf;
 struct utimbuf timebuf;
 char buf[30];

 for(i=1; i<argc; i++)
 {
  if(stat(argv[i], &statbuf) < 0 )
  {
   sprintf(buf,"%s:stat error", argv[i]);
   perror(buf);
   continue;
  }
  if(open(argv[i], O_RDWR | O_TRUNC) <0 )
  {
   
   sprintf(buf,"%s:open error", argv[i]);
   perror(buf);
   continue;
  }
  timebuf.actime = statbuf.st_atime;
  timebuf.modtime = statbuf.st_mtime;
  
  if(utime(argv[i], &timebuf) <0 )
  {
   
   sprintf(buf,"%s:utime error", argv[i]);
   perror(buf);
   continue;
  }
 }
 exit(0);
}

signal

#include <stdio.h>
#include <signal.h>

static void sig_handler(int signo);
int main()
{
 int i;
  
 for(i=0; i<100; i++)
 {
  signal(SIGINT, sig_handler);
   
  printf("[%d]\n",i);
  sleep(1);
 }

 return 0;
}

static void sig_handler(int signo)
{
 if(signo == SIGINT)
 {
  printf(" SIGINT catch !!\n");
  SIG_IGN;
 }
 return;
}