C语言 stdin 和 STDIN_FILENO 有什么区别？
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What is the difference between stdin and STDIN_FILENO?
提问by user1212697
What is the practical difference, if any, between stdinand STDIN_FILENOin C?
Cstdin和STDIN_FILENOC之间的实际区别是什么（如果有的话）？
回答by Michael
The interface. Like everyone else has said, stdinis a FILE *as defined by the standard c library. You can use some of the higher level interfaces like fread, fwrite, and fprintf. On the other hand, STDIN_FILENOis just a file descriptor (almost certainly 0). This uses a slight lower level interface through the likes of readand write.
界面。就像其他人所说的那样，stdin是FILE *标准 c 库定义的 a 。你可以使用一些像更高级别的接口fread，fwrite和fprintf。另一方面，STDIN_FILENO它只是一个文件描述符（几乎可以肯定为 0）。这通过read和 之类的方式使用了一个稍低级别的接口write。
回答by squiguy
stdinis a default FILE pointer used to get input from none other than standard in.
stdin是一个默认的 FILE 指针，用于从标准输入中获取输入。
STDIN_FILENOis the default standard input file descriptor number which is 0. It is essentially a defined directive for general use.
STDIN_FILENO是默认的标准输入文件描述符编号，即0. 它本质上是一个通用的定义指令。
回答by debug
From /usr/include/stdio.h,
从/usr/include/stdio.h,
/* Standard streams. */
extern struct _IO_FILE *stdin; /* Standard input stream. */
extern struct _IO_FILE *stdout; /* Standard output stream. */
extern struct _IO_FILE *stderr; /* Standard error output stream. */
/* C89/C99 say they're macros. Make them happy. */
#define stdin stdin
#define stdout stdout
#define stderr stderr
From /usr/include/unistd.h
从 /usr/include/unistd.h
/* Standard file descriptors. */
#define STDIN_FILENO 0 /* Standard input. */
#define STDOUT_FILENO 1 /* Standard output. */
#define STDERR_FILENO 2 /* Standard error output. */
Ex, stdin(_IO_FILEdefined in /usr/include/libio.h) is a structure data. STDIN_FILENOis a macro constant, which points to a file descriptor used by kernel.
例如，stdin（_IO_FILE在 中定义/usr/include/libio.h）是结构数据。STDIN_FILENO是一个宏常量，指向内核使用的文件描述符。
#include <stdio.h>
#include <unistd.h>
void
stdin_VS_STDIN_FILENO(void)
{
printf("stdin->_flags = %hd\n", stdin->_flags);
printf("STDIN_FILENO : %d\n", STDIN_FILENO);
}
int
main(void)
{
stdin_VS_STDIN_FILENO();
return 0;
}
回答by Udhay Devgotra
stdin : 1. A file pointer (* FILE) 2. The file descriptor table holds its address when process is created. 3. present in /usr/include/stdio.h
stdin : 1. 文件指针 (* FILE) 2. 文件描述符表在创建进程时保存其地址。3.存在于/usr/include/stdio.h
STDIN_FILENO : 1. It is a macro 2. Its nothing but an array index of a file descriptor table (default 0). 3.present in /usr/include/unistd.h
STDIN_FILENO : 1. 它是一个宏 2. 它只是文件描述符表的数组索引（默认为 0）。3.存在于/usr/include/unistd.h
Could be more clear by following code.
可以通过以下代码更清楚。
#include<stdio.h>
#include<unistd.h>
int main()
{
printf("%d\t\t%p ----- ",STDIN_FILENO,stdin);
return 0;
}
