Month: June 2016

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

static int
cat(int fd, char *file)
{
    ssize_t n;
    char buf[4096];
    
    while ((n = read(fd, buf, sizeof buf)) > 0){
        if(write(1, buf, n) < 0){
            perror("write");
            return 1;
        }
    }
    if (n < 0){
        perror(file);
        return 1;
    }
    return 0;
}

int main(int argc, char **argv)
{
    int i;
    int fd;
    int err = 0;
    
    if (argc <= 1){
        return cat(0, "stdin");
    }
    
    for (i = 1; i < argc; i++){
        if ((fd = open(argv[i], O_RDONLY)) < 0){
            perror(argv[i]);
            err = 1;
            continue;
        }
        err != cat(fd, argv[i]);
        
        if (close(fd) < 0){
            perror(argv[i]);
            err = 1;
        }
    }
    return err;
}

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

int main(){
    ssize_t n;
    char buf[4096];
    
    while ((n = read(0, buf, sizeof buf)) > 0){
        if (write(1, buf, n)< 0){
            perror("write");
            return 1;
        }
    }
    if (n < 0){
        perror("read");
        return 1;
    }
    return 0;
}

#include < unistd.h >
#include < string.h >

int main(int argc, char **argv)
{
    int i;
    
    if (argc >= 2){
        for (i = 1;;){
            write (1, argv[i], strlen(argv[i]));
            if (++i >= argc){
                break;
            }
            write (1, " ", 1);
        }
    }
    write(1, "\n", 1);
    return 0;
}

#include < sys/socket.h >
#include < netinet/in.h >

#include < unistd.h >
#include < stdio.h >
#include < string.h >
#include < arpa/inet.h >

int main()
{
    struct sockaddr_in sv_addr, cl_addr;
    socklen_t sv_len, cl_len;
    
    sv_len = sizeof sv_addr;
    if(getsockname(0, (struct sockaddr *)&sv_addr, &sv_len) < 0){
        perror("getsockname");
        return 1;
    }
    
    fprintf(stderr, "getsockname: addr = %s, port = %d\n",
            inet_ntoa(sv_addr.sin_addr),
            ntohs(sv_addr.sin_port));
    
    cl_len = sizeof cl_addr;
    if (getpeername(0, (struct sockaddr *)&cl_addr, &cl_len)<0){
        perror("getpeername");
        return 1;
    }
    
    fprintf(stderr, "getpeername: addr = %s, port = %d\n",
            inet_ntoa(cl_addr.sin_addr),
            ntohs(cl_addr.sin_port));
    write(1, "Hello\n", 6);
    return 0;
}

#include < sys/types.h >
#include < sys/socket.h >
#include < netinet/in.h >

#include 
#include 

int main()
{
    int sock_fd;
    struct sockaddr_in sv_addr;
    ssize_t n;
    
    if ((sock_fd = socket(PF_INET, SOCK_DGRAM, 0)) < 0){
        perror("socket");
        return 1;
    }
    
    memset(&sv_addr, 0, sizeof sv_addr);
    sv_addr.sin_family = AF_INET;
    sv_addr.sin_addr.s_addr =htonl(INADDR_LOOPBACK);
    sv_addr.sin_port = htons(12345);
    
    if ((n = sendto(sock_fd, "Hello\n", 6, 0,
                    (struct sockaddr *)&sv_addr, sizeof sv_addr)) < 0){
        perror("sendto");
        return 1;
    }
    return 0;
}

#include < sys/types.h >
#include < sys/socket.h >
#include < netinet/in.h >

#include < unistd.h >
#include < stdio.h >
#include < string.h >
#include < arpa/inet.h >

int main()
{
    int sock_fd;
    struct sockaddr_in sv_addr, cl_addr;
    socklen_t cl_len;
    ssize_t n;
    char buf[4096];
    if((sock_fd = socket(PF_INET, SOCK_DGRAM, 0)) < 0){
        perror("socket");
        return 1;
    }
    
    memset(&sv_addr, 0, sizeof sv_addr);
    sv_addr.sin_family = AF_INET;
    sv_addr.sin_addr.s_addr = htonl(INADDR_ANY);
    sv_addr.sin_port = htons(12345);
    
    if (bind(sock_fd, (struct sockaddr *)&sv_addr, sizeof sv_addr)<0){
        perror("bind");
        return 1;
    }
    cl_len = sizeof cl_addr;
    
    if ((n = recvfrom(sock_fd, buf, sizeof buf, 0,
                      (struct sockaddr *)&cl_addr, &cl_len)) < 0){
        perror("recvfrom");
        return 1;
    }
    fprintf(stderr, "UDP from addr = %s, port = %d\n",
            inet_ntoa(cl_addr.sin_addr),
            ntohs(cl_addr.sin_port));
    write(1, buf, n);
    return 0;
}

#include 
#include 

int main(){
    char name[256];
    
    if(gethostname(name, sizeof name)<0){
        perror("gethostname");
        return 1;
    }
    printf("%s\n", name);
    return 0;
}

OSなどのシステム情報を取得するにはunameを使います。

#include < sys/utsname.h >

#include < stdio.h >

int main()
{
    struct utsname buf;
    
    if (uname(&buf) < 0){
        perror("uname");
        return 1;
    }
    
    printf("%s %s %s %s %s\n",
           buf.sysname,
           buf.nodename,
           buf.release,
           buf.version,
           buf.machine);
    return 0;
}

#include < sys/time.h >

#include < time.h >
#include < stdio.h >

int main(){
    struct timeval tv;
    struct tm tm;
    
    tm.tm_sec = 0;
    tm.tm_min = 0;
    tm.tm_hour = 0;
    tm.tm_mday = 1;
    tm.tm_mon = 0;
    tm.tm_year = 138;
    tm.tm_isdst = 0;
    tv.tv_sec = mktime(&tm);
    tv.tv_usec = 0;
    
    if (settimeofday(&tv, NULL) < 0){
        perror("settimeofday");
        return 1;
    }
    return 0;
}

#include < sys/time.h >
#include < time.h >
#include < stdio.h >

int main()
{
    struct timeval tv;
    
    if (gettimeofday(&tv, NULL) < 0){
        perror("gettimeofday");
        return 1;
    }
    printf("%s", ctime(&tv.tv_sec));
    return 0;
}