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*
<>注意
当在Linux系统中打开一个文件时，标准输入、标准输出、标准错误输出是默认打开的
指定重定向 文件file_redirect、file_stdout（必须是已经存在的）
为了验证是否实验成功可以事先在文件中写入一句话：Successful file redirection
*
<>标准输入重定向 stdin 0
* 使用close close(0);//关闭标准输入 int fd; char buf[1024];
fd=open("file_redirect",O_RDOONLY); //1.通过printf函数验证标准输入是否重定向到文件file_redirect
printf("fd=%d",fd); //2.通过read、write函数验证标准输入是否重定向到文件file_redirect
read(0,buf,20);//读20个字符到buf write(1,buf,20);//写20个字符到标准输出 close(fd);
*
<>标准输出重定向 stdout 1
* 使用dup2函数 int fd1; fd1=open("file_stdout",O_WRONLY | O_TRUNC); dup2(fd1,1);
printf("Successful file redirection"); close(fd1);
*
验证：(执行下列命令)
gcc file.c -o file
./file
cat file_stdout
*
<>标准输出重定向 stdout 1
*
使用fcntl函数
使用fcntl函数需要注意一定要关闭标准输出
int fd2; fd2=open("file_stdout",O_WRONLY | O_TRUNC); close(1);
fcntl(fd2,F_DUPFD,1); printf("Successful file redirection"): close(fd2);
验证方法同上
如有不足之处，请大家指出，谢谢！！！
