linux 系统指令

size_t write(int fildes, const void *buf, size_t nbytes)

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

int main(void) {
	const size_t WRITE_INFO_LEN = 18;
    const size_t ERR_INFO_LEN   = 46;
    const char* WEITE_INFO = "Here is some data\n";
    const char* ERR_INFO   = "A write error has occurred on file descriptor 1 \n";
    // 向fd1(屏幕)写入
    if (write(STDOUT_FILENO, WEITE_INFO, WRITE_INFO_LEN) != WRITE_INFO_LEN) {
        write(STDERR_FILENO, ERR_INFO, ERR_INFO_LEN);
    }
    return 0;
}

#include <unistd.h>

size_t read(int fildes, void *buf, size_t nbytes)

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

int main(void) {
	const int READ_INFO_LEN      = 128;
	const int READ_ERR_INFO_LEN  = 26;
	const int WRITE_ERR_INFO_LEN = 27;
    char buffer[READ_INFO_LEN];

    // 从fd0(键盘)中读入
    int read_res = read(STDIN_FILENO, buffer, READ_INFO_LEN);
    if (read_res == -1) {
        write(STDERR_FILENO, "A read error has occurred\n", READ_ERR_INFO_LEN);
    }
    // 向fd1(屏幕)写入
    int write_res = write(STDOUT_FILENO, buffer, read_res);
    if (write_res != read_res) {
        write(STDERR_FILENO, "A write error has occurred\n", WRITE_ERR_INFO_LEN);
    }
    return 0;
}

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

int open(const char *path, int oflags);
int open(const char *path, int oflags, mode_t mode);

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

int main(void) {
    char block[1024];
    int nread;

    int in  = open("file.in", O_RDONLY);
    int out = open("file.out", O_WRONLY|O_CREAT, S_IRUSR|S_IWUSR);
    while((nread = read(in, block, sizeof(block))) > 0) {
        write(out, block, nread);
    }
    return 0;
}

// 读文件到内存,返回文件信息结构指针
FILE *fopen(char *file, char *open_mode)

void (*signal (int sig, void (*func)(int)))(int);

signal(registered signal, signal handler)

// signal.c
#include <signal.h>
#include <unistd.h>
#include <stdlib.h>
#include <string.h>

static void sig_usr(int signo) {
    if(signo == SIGUSR1) {
        write(STDOUT_FILENO, "received SIGUSR1\n", 17);
    } else if (signo == SIGUSR2) {
        write(STDOUT_FILENO, "received SIGUSR2\n", 17);
    } else {
        printf("received signal %d\n", signo);
    }
}

int main(int argc, char *argv[]) {
    struct sigaction sa;
    sa.sa_handler = sig_usr;
    sigemptyset(&sa.sa_mask);
    sa.sa_flags = 0;

    if(sigaction(SIGUSR1, &sa, NULL) == -1) {
        perror("sigaction SIGUSR1");
        exit(1);
    }
    if(sigaction(SIGUSR2, &sa, NULL) == -1) {
        perror("sigaction SIGUSR2");
        exit(1);
    }

    // 等待信号
    for(;;) {
        pause();
    }

    return 0;
}

int raise (signal sig);

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

void signalHandler(int signum){
    printf("interrupt signal %d received\n", signum);
    // 清理并关闭
    exit(signum);
}

int main(void){
    // 注册信号 SIGINT 和信号处理程序
    signal(SIGINT, signalHandler);

    for(int i = 0; i < 5; i++){
        printf("going to sleep...\n");
        if(i == 3){
           raise(SIGINT);
        }
        sleep(1);
    }
    return 0;
}