


Detailed introduction to file descriptors and file pointers under Linux
This article mainly introduces the detailed information about file descriptors and file pointers under Linux. Friends in need can refer to
File descriptors under Linux Descriptors and file pointers
File identifier:
First of all, let’s understand what a file identifier is?
File description A symbol is a term in computer science and is an abstract concept used to express a reference to a file. In Linux, each process will save a file descriptor table in the process control block (PCB). The file descriptor is the
indexof this table. Each table has There is a pointer to the open file. Each Linux process should have three standard file descriptors, corresponding to three standard streams.
IntegerValueConstant0Standard inputFILE ##1Standard outputSTDOUT_FILENOstdout2Standard errorSTDERR_FILENOstderr opens an existing file or creates a new file, the kernel returns a file descriptor to the process. In programming, some low-level programming often revolves around file descriptors. However, the concept of file descriptors is often only applicable to operating systems such as UNIX and Linux.Operations related to file descriptors:
File descriptor generation | open(), socket(), pipe(), etc. |
---|---|
read(), write(), s | (), f |
Operations related to plural file descriptorsselect(), poll(), etc. | |
close(), dup(), etc. | |
variablepoints to a file. This pointer is called a file pointer. Through the file pointer, we can perform various operations on the pointed file. The C language uses file pointers instead of file descriptors as I/O handles. The file pointer points to a data structure called the FILE structure in the user area of the process. The FILE structure contains a buffer and a file descriptor.
The file pointer is a common format of C language, so it is relatively easier to transplant.
We usually obtain the file pointer:
1 |
|
pointed to by the file pointer is unique.
Conversion of file descriptors and file pointers:1 2 3 |
|
The first parameter of fdopen is an open file descriptor, and mode indicates the opening methodString, the same as fopen, such as "w" or "r".
filenoFunction, it returns the file descriptor corresponding to the file stream, and returns - on failure 1.
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