linux －－dup dup2 文件描述符重定向函数－－输入输出重定向

#include <sys/stat.h>
#include <string.h>
#include <fcntl.h>
#include <io.h>

int main(void)
{
#define STDOUT 1 //标准输出文件描述符 号

int nul, oldstdout;
char msg[] = "This is a test";

/* create a file */

//打开一个文件，操作者具有读写权限 如果文件不存在就创建
nul = open("DUMMY.FIL", O_CREAT | O_RDWR,S_IREAD | S_IWRITE);

/* create a duplicate handle for standard
output */

//创建STDOUT的描述符备份
oldstdout = dup(STDOUT);
/*redirect standard output to DUMMY.FILE by duplicating the file handle onto the file handle for standard output.*/

//重定向nul到STDOUT
dup2(nul, STDOUT);

/* close the handle for DUMMY.FIL */

//重定向之后要关闭nul
close(nul);

/* will be redirected into DUMMY.FIL */

//写入数据
write(STDOUT, msg, strlen(msg));

/* restore original standard output handle */

//还原
dup2(oldstdout, STDOUT);

/* close duplicate handle for STDOUT */
close(oldstdout);

return 0;
}

//结果就是msg写到了文件中而不是STDOUT