[C crazy handouts] (16) C language file operations, C language handouts operations

[C crazy handouts] (16) C language file operations, C language handouts operations

1. Basic concepts of Files

 

Stores datasets on external media. A dataset name is the file name.

 

File category:

 

1) user perspective: common files and Device Files

2) Storage content:

 

Ascii file (Text File ):

 

Storage Process: Find the corresponding ascii code value based on the text ----> convert to binary -->

Writing to file

 

Read process: Binary --> 10 hexadecimal --> Find the corresponding character --> display

 

 

 

Binary file:

 

Binary data access

 

File Operation Process:

 

1) import the header file stdio. h

 

2) define the file pointer

 

3) open the file

4) operation files

 

5) close the file

 

File Operation Principle

 

 

 

2. File pointer

 

FILE struct

FILE * fp; struct pointer

 

Purpose: store the first address of a file, pointing to a file

 

 

3. Open and Close a file

 

 

Open fopen (file name, operation method );

 

Fopen ("a.txt", "r ");

// A.txt is found in the products directory by default./Users/apple/Library/Developer/Xcode/DerivedData/C15-Integrated Project-cmassyrpkwjxularuygrjqhojbwj/Build/Products/Debug

 

Fopen ("/Users/apple/Desktop/a.txt", "r ");

 

Operation Method:

 

R w a B + t

Read/write append level-2 read/write text

 

W -- when writing a file, if the file does not exist, create

'Overwrite if it exists

 

R + w + wb + a +

 

Close the file:

 

Fclose (File pointer );

 

 

4. file operation functions

 

1) Reading and Writing of bytes-type data

 

Write:

Fputc ('characters', file pointer );

Char c = 'a ';

Fputc (c, fp );

 

Read:

 

Char ch = fgetc (fp );

 

2) Reading and Writing string data

 

Write:

Fputs (array name/pointer name, fp); // fputs (array name, stdout );

 

Read:

Fgets (array name/pointer name, length, fp );

 

The actual number of characters read by fgets is-1.

 

1) The end of \ n and the end of EOF

 

3) read and write data blocks

 

Write:

 

Fwrite (write variable address, data block size, number of blocks, fp );

 

Int a = 123;

Fwrite (& a, sizeof (int), 1, fp );

 

Struct Student stu1;

Fwrite (& stu1, sizeof (struct Student), 1, fp );

 

Read:

Struct Student s1;

Fread (variable address, data block size, number of blocks, fp)

 

Fread (& s1, sizeof (struct Student), 1, fp );

// Use s1 for output

 

4) formatted read and write

 

Write Data and read data in a certain format

 

Write:

Fprintf (File pointer, "formatted string", variable list );

 

Fprintf (fp, "% d, % c, % d #", 10, 'A', 20 );

 

10, a, 20 #10, a, 20 #10, a, 20 #

 

Read

 

Fscanf (fp, "% d, % c, % d #", & a, & ch, & B );

 

Fprintf (fp, "% d, % s, % d", 20, "abc", 30 );

 

Fscanf (fp, "% d, % s, % d", & a, str, & B );

 

Str = abc, 30

 

Changed:

 

Fprintf (fp, "% d, % d, % s", 20, 20, "abc ");

Fscanf (fp, "% d, % d, % s", & a, & B, str );

 

 

5. Random File Reading

Set the position of the file's header pointer

 

The default fp is the first address pointing to the file.

 

1) rewind (fp); // fp points to the first address

 

2) fseek (fp, offset distance, starting point );

 

Fseek (fp, 32L, SEEK_SET); // offset 32 bytes from the file header

 

 

 

6. File Detection Functions

 

Feof () is used to check whether the file ends

 

If the end is not 0

To end 1

Disadvantage: One more execution

 

 

7. Introduction to other header files in C Language

 

Math. h

Stdio. h

Stdlib. h

Time. h

String. h