What is the difference between stdin and STDIN_FILENO?
CC Problem Overview
What is the practical difference, if any, between stdin and STDIN_FILENO in C?
C Solutions
Solution 1 - C
The interface. Like everyone else has said, stdin is 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_FILENO is just a file descriptor (almost certainly 0). This uses a slight lower level interface through the likes of read and write.
Solution 2 - C
stdin is a default FILE pointer used to get input from none other than standard in.
STDIN_FILENO is the default standard input file descriptor number which is 0. It is essentially a defined directive for general use.
Solution 3 - C
From /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
/* 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_FILE defined in /usr/include/libio.h) is a structure data. STDIN_FILENO is a macro constant, which points to a file descriptor used by kernel.
#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;
}
Solution 4 - C
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_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
Could be more clear by following code.
#include<stdio.h>
#include<unistd.h>
int main()
{
printf("%d\t\t%p ----- ",STDIN_FILENO,stdin);
return 0;
}
Solution 5 - C
The STDIN_FILENO in the linux header #include "unistd.h" is just a macro for 0 which stands for the stdin for the pipe, when you are using Linux pipe.