ctrl+c,ctrl+d,ctrl+z在linux中意义

#include <errno.h>
#include <fcntl.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <stdlib.h>
#include <string.h>

#define BUFFER_SIZE 1024

int main(int argc, char *argv[])
{
    int fd;
    char buffer[BUFFER_SIZE];
    if(argc!=2)
    {
        fprintf(stderr,"Usage:%s outfilename\n\a",argv[0]);
        exit(EXIT_FAILURE);
    }
    if((fd=open(argv[1],O_WRONLY|O_CREAT|O_TRUNC,S_IRUSR|S_IWUSR))==-1)
    {
        fprintf(stderr,"Open %s Error:%s\n\a",argv[1],strerror(errno));
        exit(EXIT_FAILURE);
    }
    if(dup2(fd,fileno(stdout))==-1)
    {
        fprintf(stderr,"Redirect Standard Out Error: %s\n\a",strerror(errno));
        exit(EXIT_FAILURE);
    }
    fprintf(stderr,"Now, please input string");
    fprintf(stderr,"(To quit use CTRL+D)\n");
    while(1)
    {
        fgets(buffer,BUFFER_SIZE,stdin);
        if(feof(stdin))
            break;
        write(fileno(stdout),buffer,strlen(buffer));
    }
    exit(EXIT_SUCCESS);
}