Stream is the operation object of the standard IO core

After a program starts executing, three streams will be automatically opened.

The difference between standard output stream and standard error output stream

Standard stream interview questions

Operations related to input and output of files //Open the file, read the file, write the file, close the file //I input O output

1. Standard IO//The file-related operations in the standard C library belong to library functions 2. LinuxIO//The file-related operations provided by the Linux system are system calls.

//Standard IO exists in the buffer //Not adding ' ' means full cache. When the buffer area is full, it will be processed by the operating system for unified printing. //The default size of the cache area is 1024 bytes

//With the addition of , the full cache becomes a line cache. The output content will not stay in the cache area. When ' ' is encountered, it will be handed over to the operating system for processing and then printed on the terminal. //Note: The concept of line caching will only exist when the output object is a terminal.

Function: open file

Parameter description

return value FILE* pointer, file stream pointer, FILE is a structure. Every time a file is opened, the kernel will open up a space to save the relevant information obtained by opening the file. success: Return FILE* (non-empty)//Stream stream is the core object of standard IO fail: Return NULL

Function: Read one character at a time (read literally)

Parameter description

return value success: The ascii value corresponding to the actually read character Failure: //When the tail of the file is read, the return value is EOF, which is -1 The return value is -1 Return EOF(-1) #define EOF -1

Function: Write a character to the file

Parameter description

Function: Close the file, refresh the cache area, and clear the contents of the cache area.

Parameter description

return value success: Return 0 fail: Return -1

Parameter description

return value none

Function: Function to print error message There is a global variable in the Linux system. errno is used to save the error message number. The printing of error output information is based on the error number.

Parameter description

Return value: char * The first address of the error cause string "No such file or directory"

Function: Read one line at a time ( The newline character is used as the terminator of reading)

Parameter description

Return value: success: char * //The first address of the line of string read out fail: Returns NULL, returns NULL when reading to the end of the file

Function: Write a string each time

Parameter description

Return value: success: >= 0 //non-negative number fail: Return EOF

Function: Read content at specified size Read one segment at a time (note that one segment is measured in blocks)

Parameter description

Return value: success: Number of blocks actually read The actual number of records read Number of objects actually read It cannot be said that it represents the actual number of bytes read. fail: less than or equal to 0

Function: write in blocks

Parameter description

Return value: success: Number of blocks actually written fail: less than 0

sprintf

fprintf

printf sprintf fprintf difference

Function: memory setting function, memset is an initialization function, The function is to set everything in a certain block of memory to the specified value.

Parameter description

Return value: The starting address of the set memory space

Function: The file pointer is a member variable in the FILE structure. Move the position of the file pointer.

Parameter description

Return value: Success: 0 Failure: EOF -1

Function: Get the position of the file pointer The file pointer's position index starts from 0

Parameter description

return value Success: Returns the position of the current file pointer Failure: EOF