Category: C++

#include < sys/types.h >
#include < unistd.h >

#include < stdio.h >

static void
printuid()
{
    printf("uid = %d euid = %d\n",
           (int)getuid(), (int)geteuid());
}

int main() {
    uid_t uid, euid;
    
    uid = getuid();
    euid = geteuid();
    
    printuid();
    
    if (seteuid(uid) < 0){
        perror("seteuid");
        return 1;
    }
    printuid();
    
    if (seteuid(euid)<0){
        perror("seteuid");
        return 1;
    }
    printuid();
    
    return 0;
}

getuid/geteuid/getgid/getegidは、それぞれ自分のプロセスの実ユーザID、実行ユーザID、実グループID、実行グループIDを取得します。

#include < unistd.h >
#include < sys/types.h >

#include < stdio.h >

int main()
{
    uid_t uid, euid;
    gid_t gid, egid;
    
    uid = getuid();
    euid = geteuid();
    gid = getgid();
    egid = getegid();
    
    printf("uid = %d, euid = %d, gid = %d, egid = %d\n",
           (int)uid, (int)euid, (int)gid, (int)egid);
    
    return 0;
}

#include < unistd.h >

#include < stdio.h >
#include < stdlib.h >

int main()
{
    if (chdir("/tmp")< 0){
        perror("chdir");
        return 1;
    }
    system("pwd");
    return 0;
}

wait3に引数pidが増えただけです。

#include < sys/types.h >
#include < sys/time.h >
#include < sys/resource.h >
#include < sys/wait.h >

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

int
main()
{
    int status;
    pid_t pid;
    struct rusage usage;
    
    if ((pid = fork()) < 0){
        perror("fork");
        return 1;
    } else if (pid == 0){
        write(1, "chlid process\n", 14);
        _exit(12);
    }
    write(1, "parent process\n", 15);
    
    if ((pid = wait4(pid, status, 0, &usage)) < 0){
        perror("wait4");
        return 1;
    }
    if(WIFEXITED(status)){
        printf(
        "pid = %d exited with status = %d\n",
               (int)pid, WEXITSTATUS(status));
    }
    
    printf(
    "user time = %ld.%06ld\n"
    "system time = %ld.%06ld\n",
    usage.ru_utime.tv_sec, usage.ru_utime.tv_usec,
           usage.ru_stime.tv_sec, usage.ru_stime.tv_usec);
    return 0;
}

#include < sys/types.h >
#include < sys/time.h >
#include < sys/resource.h >
#include < sys/wait.h >

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

int main()
{
    int status;
    pid_t pid;
    struct rusage usage;
    
    if ((pid = fork())< 0){
        perror("fork");
        return 1;
    } else if (pid == 0){
        write(1, "child process\n", 14);
        _exit(12);
    }
    write(1, "parent process\n", 15);
    
    if ((pid = wait3(&status, 0, &usage)) < 0) {
        perror("wait3");
        return 1;
    }
        if(WIFEXITED(status)){
            printf(
            "pid=%d exited with status = %d\n",
                   (int)pid, WEXITSTATUS(status));
        }
    printf(
    "user time = %ld.%06ld\n"
           "system time = %ld.%06ld\n",
           usage.ru_utime.tv_sec, usage.ru_utime.tv_usec,
           usage.ru_stime.tv_sec, usage.ru_stime.tv_usec);
    return 0;
        
}

#include < sys/types.h >
#include < sys/wait.h >

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

int mian()
{
    int status;
    pid_t pid;
    
    if ((pid = fork()) < 0){
        perror("fork");
        return 1;
    } else if (pid == 0){
        write(1, "child process\n", 14);
        _exit(12);
    }
    write(1, "parent process\n", 15);
    
    if((pid = waitpid(pid, &status, 0)) < 0){
        perror("waitpid");
        return 1;
    }
    if(WIFEXITED(status)){
        printf(
        "pid = %d exited with status = %d\n",
               (int)pid, WEXITSTATUS(status));
    }
    return 0;
}

#include < unistd.h >

int
main()
{
    _exit(0);
    
    return 0;
}

#include < unistd.h >

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

int
main()
{
    pid_t pid;
    char *argv[3];
    extern char **environ;
    
    if((pid = fork())< 0){
        perror("fork");
        return 1;
    } else if(pid == 0){
        argv[0]="echo";
        argv[1]="Hello, from child";
        argv[2]= NULL;
        execve("/bin/echo", argv, environ);
        _exit(1);
    }
    write(1, "Hello, from parent\n", 19);
    return 0;
}

新しい子プロセスの作成には、forkを使います。

#include < sys/types.h >
#include < unistd.h >

#include 

int
main()
{
    pid_t pid;
    
    if ((pid = fork()) < 0){
        perror("fork");
        return 1;
    } else if (pid == 0){
        write(1, "child process\n", 14);
        _exit(0);
    }
    write(1, "parent process\n", 15);
    return 0;
}

ハッシュサーチは検索は圧倒的に高速です。データをテーブルに格納する際に簡単な式でキーを割り当て、そのキーでダイレクトに飛べる場所にデータを格納しておきます。

#include 
#include 
#include 

#define HASH_SIZE 4096

static char **Str[HASH_SIZE];
static int Strmax[HASH_SIZE];

int strno(char *str)
{
    static char *null="";
    char *p,*ptr,*ptrc;
    int i;
    unsigned n;
    
    if(str==NULL){
        ptr=null;
    }
    else{
        ptr=str;
    }
    
    n=0;
    for(ptrc=ptr;(*ptrc)!='\0';ptrc++){
        n+=(unsigned)(*ptrc);
    }
    n%=HASH_SIZE;
    for(i=0;i