Does dup2 close file descriptor?
So, when you call dup2(a, b) , either one of these is true: a == b . In this case, nothing happens and dup2() returns prematurely. No file descriptors are closed.
Does dup2 close Oldfd?
dup2() The dup2() system call performs the same task as dup(), but instead of using the lowest-numbered unused file descriptor, it uses the file descriptor number specified in newfd. * If oldfd is a valid file descriptor, and newfd has the same value as oldfd, then dup2() does nothing, and returns newfd.
How use dup2 Linux?
The syntax of dup2() function is:
- int dup2(int old_file_descriptor, int new_file_descriptor);
- #include
- $ man dup2.
- 15 41.
- #include #include #include #include
- int number1, number2, sum;
- int input_fds = open(“./input. txt”, O_RDONLY);
- dup2(input_fds, STDIN_FILENO)
What does the dup2 function do?
The dup2() function duplicates an open file descriptor. Specifically, it provides an alternate interface to the service provided by the fcntl() function using the F_DUPFD constant command value, with fildes2 for its third argument. The duplicated file descriptor shares any locks with the original.
What does DUP and dup2 do?
The difference between dup and dup2 is that dup assigns the lowest available file descriptor number, while dup2 lets you choose the file descriptor number that will be assigned and atomically closes and replaces it if it’s already taken.
Can dup2 fail?
All file descriptors available to the process are currently open. The dup2() function shall fail if: The fildes argument is not a valid open file descriptor or the argument fildes2 is negative or greater than or equal to {OPEN_MAX}.
What is DUP and dup2?
What does dup2 return?
The dup2() function returns a descriptor with the value fildes2. The descriptor refers to the same file as fildes, and it will close the file that fildes2 was associated with. For more information about the processing which may occur when the file is closed, see close()–Close File or Socket Descriptor.
What is the difference between DUP and dup2?
What is dup2?
The dup2() function returns a descriptor with the value fildes2. The descriptor refers to the same file as fildes, and it will close the file that fildes2 was associated with. If the original file descriptor was opened in text mode, data conversion is also done on the duplicated file descriptor.
What is difference between dup and dup2?
How does dup2 close a file descriptor?
If the file descriptor newfd was previously open, it is closed before being reused; the close is performed silently (i.e., any errors during the close are not reported by dup2 ()). The steps of closing and reusing the file descriptor newfd are performed atomically.
How to use dup2 in a system call?
A tricky use of dup2 () system call: As in dup2 (), in place of newfd any file descriptor can be put. Below is a C implementation in which the file descriptor of Standard output (stdout) is used. This will lead all the printf () statements to be written in the file referred by the old file descriptor.
What is the difference between DUP ( ) and dup2 ( )?
The dup2() system call is similar to dup() but the basic difference between them is that instead of using the lowest-numbered unused file descriptor, it uses the descriptor number specified by the user. Syntax: int dup2(int oldfd, int newfd); oldfd: old file descriptor newfd new file descriptor which is used by dup2() to create a copy.
Is there a dup2 descriptor that returns einval?
On some systems dup2 () also sometimes returns EINVAL like F_DUPFD . If newfd was open, any errors that would have been reported at close (2) time are lost. A careful programmer will not use dup2 () or dup3 () without closing newfd first.