c++ string

string-----------

#include <string>
#include <iostream>
using std::string;
int main(){
    string aa="hao";
    std::cout<<aa;
    return 0;
}

基本输出-------------

#include <stdio.h>
main()
{
        int c;
        while ((c = getchar()) != EOF)
                putchar(c);
}

read---------

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#define BUFFSIZE        4096

int
main(void)
{
        int             n;
        char    buf[BUFFSIZE];

        while ((n = read(STDIN_FILENO, buf, BUFFSIZE)) > 0)
                if (write(STDOUT_FILENO, buf, n) != n)
                        printf("write error");

        if (n < 0)
                printf("read error");

        exit(0);
}

#########while语句的省略写法，
管道和fork-----------

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#define MAXLINE 4096 
int
main(void)
{
    int     n;
    int     fd[2];
    pid_t   pid;
    char    line[MAXLINE];

    if (pipe(fd) < 0)
        printf("pipe error");
    if ((pid = fork()) < 0) {
        printf("fork error");
    } else if (pid > 0) {       /* parent */
        close(fd[0]);
        write(fd[1], "hello world\n", 12);
    } else {                /* child */
        close(fd[1]);
        n = read(fd[0], line, MAXLINE);
        write(STDOUT_FILENO, line, n);
    }
    exit(0);
}

gettimeofday-------

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

int main(int argc, char * argv[]){

    struct timeval tv;                //(1)
    while(1){
        gettimeofday(&tv, NULL);      //(2)
        printf("time %u:%u\n", tv.tv_sec, tv.tv_usec);
        sleep(2);
    }
    return 0;

}