Common functions for Linux File Operations

Linux-fopen-fclose-fread-fwrite and other functions

Clearerr (error flag for clearing file streams)

Related functions

Feof

Header file

# Include <stdio. h>

Define functions

Void clearerr (File * stream );

Function Description

Clearerr () clears the error flag used by the file stream specified by the stream parameter.

Return Value

Fclose (close file)

Related functions

Close, fflush, fopen, setbuf

Header file

# Include <stdio. h>

Define functions

Int fclose (File * stream );

Function Description

Fclose () is used to close files opened by fopen. This action writes data in the buffer zone to a file and releases the file resources provided by the system.

Return Value

If the file is successfully closed, 0 is returned. If an error occurs, EOF is returned and the error code is saved to errno.

Error Code

Ebadf indicates that the parameter stream is not an open file.

Example

See fopen ().

Fdopen (convert file description to file pointer)

Related functions

Fopen, open, fclose

Header file

# Include <stdio. h>

Define functions

File * fdopen (INT Fildes, const char * mode );

Function Description

Fdopen () converts the file description of Fildes to the corresponding file pointer and returns the result. The mode string represents the stream format of the file pointer, which must be the same as the read/write mode of the original file description. For more information about the mode string format, see fopen ().

Return Value

Returns the file pointer to the stream when the conversion is successful. If the Error Code fails, null is returned, and the error code is stored in errno.

Example

# Include <stdio. h>
Main ()
{
File * fp = fdopen (0, "W + ");
Fprintf (FP, "% s \ n", "hello !");
Fclose (FP );
}

Run

Hello!

Feof (check whether the file stream has read the end Of the file)

Related functions

Fopen, fgetc, fgets, fread

Header file

# Include <stdio. h>

Define functions

Int feof (File * stream );

Function Description

Feof () is used to detect whether the end of the file is read, and the ending number stream is the object pointer returned by fopen. If the end of the file is reached, a non-zero value is returned. Otherwise, 0 is returned.

Return Value

A non-zero value indicates that the end of the file has been reached.

Fflush (update buffer)

Related functions

Write, fopen, fclose, setbuf

Header file

# Include <stdio. h>

Define functions

Int fflush (File * stream );

Function Description

Fflush () forces the data in the buffer to be written back to the file specified by the parameter stream. If the parameter stream is null, fflush () updates all open file data.

Return Value

0 is returned for success, EOF is returned for failure, and the error code is stored in errno.

Error Code

The file specified by the stream parameter is not open, or the open status is read-only. For other error codes, see write ().

Fgetc (one character read from the file)

Related functions

Open, fread, fscanf, GETC

Header file

Include <stdio. h>

Define functions

NT fgetc (File * stream );

Function Description

Fgetc () reads a character from the file indicated by the stream parameter. If you read the end Of the file without data, the EOF is returned.

Return Value

GETC () returns the read characters. If EOF is returned, it indicates the end of the file.

Example

# Include <stdio. h>
Main ()
{
File * FP;
Int C;
Fp = fopen ("exist", "R ");
While (C = fgetc (FP ))! = EOF)
Printf ("% C", c );
Fclose (FP );
}

Fgets (read a string from the file)

Related functions

Open, fread, fscanf, GETC

Header file

Include <stdio. h>

Define functions

Har * fgets (char * s, int size, file * stream );

Function Description

Fgets () is used to read characters from the file referred to by the parameter stream to the memory space referred to by the parameter S until a line break occurs, the end of the file is read, or the size-1 character is read, finally, null is added as the string.

Return Value

If gets () is successful, the S pointer is returned. If null is returned, an error occurs.

Example

# Include <stdio. h>
Main ()
{
Char s [80];
Fputs (fgets (s, 80, stdin), stdout );
}

Run

This is a test
This is a test

Fileno (returns the file description used by the file Stream)

Related functions

Open, fopen

Header file

# Include <stdio. h>

Define functions

Int fileno (File * stream );

Function Description

Fileno () is used to obtain the file description used by the file stream specified by the parameter stream.

Return Value

Returns the description of a file.

Example

# Include <stdio. h>
Main ()
{
File * FP;
Int FD;
Fp = fopen ("/etc/passwd", "R ");
FD = fileno (FP );
Printf ("FD = % d \ n", FD );
Fclose (FP );
}

Run

FD = 3

Fopen (open a file)

Related functions

Open, fclose

Header file

# Include <stdio. h>

Define functions

File * fopen (const char * path, const char * mode );

Function Description

The parameter path string contains the path and file name of the file to be opened. The parameter mode string represents the stream format.
Mode has the following forms of strings:
R: open a read-only file, which must exist.
R + open a readable file, which must exist.
W. Open and write only the file. If the file exists, the file length is 0, indicating that the file content will disappear. If the file does not exist, the file is created.
W + open the readable and writable file. If the file exists, the file length is cleared to zero, that is, the file content disappears. If the file does not exist, the file is created.
A. Open and write-only files as an attachment. If the file does not exist, the file will be created. If the file exists, the written data will be added to the end of the file, that is, the original content of the file will be retained.
A + opens readable and writable files by appending them. If the file does not exist, the file will be created. If the file exists, the written data will be added to the end of the file, that is, the original content of the file will be retained.
The preceding morphological string can be added with a B character, such as a combination of Rb, W + B, and AB +. The B character is added to indicate that the file opened by the function library is a binary file, rather than text files. However, this character is ignored in the POSIX System in Linux. The new file created by fopen () has the s_irusr | s_iwusr | s_irgrp | s_iwgrp | s_iroth | s_iwoth (0666) Permission. For the File Permission, see umask value.

Return Value

After the file is successfully opened, the file pointer pointing to the stream will be returned. If the file fails to be opened, null is returned and the error code is stored in errno.

Additional instructions

In general, after opening a file, some file reading or writing operations will be performed. If opening a file fails, the subsequent read/write operations will not proceed smoothly. Therefore, in the fopen () then, make error judgment and handling.

Example

# Include <stdio. h>
Main ()
{
File * FP;
Fp = fopen ("noexist", "a + ");
If (FP = NULL) return;
Fclose (FP );
}

Fputc (write a specified character to the file Stream)

Related functions

Fopen, fwrite, fscanf, putc

Header file

# Include <stdio. h>

Define functions

Int fputc (int c, file * stream );

Function Description

Fputc converts parameter C to unsigned char and writes it to the file specified by parameter stream.

Return Value

Fputc () returns the successfully written character, that is, the parameter C. If EOF is returned, the write operation fails.

Example

# Include <stdio. h>
Main ()
{
File * FP;
Char A [26] = "abcdefghijklmnopqrstuvwxyz ";
Int I;
Fp = fopen ("noexist", "W ");
For (I = 0; I <26; I ++)
Fputc (A [I], FP );
Fclose (FP );
}

Fputs (write a specified string into the file)

Related functions

Fopen, fwrite, fscanf, fputc, putc

Header file

# Include <stdio. h>

Define functions

Int fputs (const char * s, file * stream );

Function Description

Fputs () is used to write the string referred to by parameter S to the file referred to by parameter stream.

Return Value

If it succeeds, the number of written characters is returned. If it returns EOF, an error occurs.

Example

See fgets ().

Fread (reads data from a file Stream)

Related functions

Fopen, fwrite, fseek, fscanf

Header file

# Include <stdio. h>

Define functions

Size_t fread (void * PTR, size_t size, size_t nmemb, file * stream );

Function Description

Fread () is used to read data from a file stream. The stream parameter is an opened file pointer. the PTR parameter points to the data space to be read. The number of characters read is determined by the size * nmemb parameter. Fread () returns the number of nmemb actually read. If this value is smaller than the nmemb parameter, it indicates that the file may be read at the end or an error occurs. In this case, feof () must be used () or ferror () to determine what happens.

Return Value

Returns the number of nmemb instances actually read.

Additional instructions

Example

# Include <stdio. h>
# Define nmemb 3
Struct Test
{
Char name [20];
Int size;
} S [nmemb];
Main ()
{
File * stream;
Int I;
Stream = fopen ("/tmp/fwrite", "R ");
Fread (S, sizeof (struct test), nmemb, stream );
Fclose (Stream );
For (I = 0; I <nmemb; I ++)
Printf ("name [% d] = %-20 s: Size [% d] = % d \ n", I, S [I]. name, I, S [I]. size );
}

Run

Name [0] = Linux! Size [0] = 6
Name [1] = FreeBSD! Size [1] = 8
Name [2] = Windows2000 size [2] = 11

Freopen (open a file)

Related functions

Fopen, fclose

Header file

# Include <stdio. h>

Define functions

File * freopen (const char * path, const char * mode, file * stream );

Function Description

The parameter path string contains the path and file name of the file to be opened. For details about the parameter mode, see fopen. The stream parameter is an opened file pointer. Freopen () will close the file stream opened by the original stream, and then open the file with the path parameter.

Return Value

After the file is successfully opened, the file pointer pointing to the stream will be returned. If the file fails to be opened, null is returned and the error code is stored in errno.

Example

# Include <stdio. h>
Main ()
{
File * FP;
Fp = fopen ("/etc/passwd", "R ");
Fp = freopen ("/etc/group", "R", FP );
Fclose (FP );
}

Fseek (read/write location of a mobile file Stream)

Related functions

Rewind, ftell, fgetpos, fsetpos, lseek

Header file

# Include <stdio. h>

Define functions

Int fseek (File * stream, long offset, int whence );

Function Description

Fseek () is used to move the read/write location of a file stream. The stream parameter is an opened file pointer, And the offset parameter is the number of read/write locations to be moved Based on the whence parameter.

Parameters

Whence is one of the following:
The offset displacement from the beginning of the seek_set file is the new read/write location. Seek_cur increases the offset displacement at the current read/write position.
Seek_end points the read/write position to the end of the file and then increases the offset displacement.
When the whence value is seek_cur or seek_end, the offset parameter allows negative values.
The following are special usage methods:
1) to move the read/write location to the beginning of the file: fseek (File * stream, 0, seek_set );
2) to move the read/write location to the end of the file: fseek (File * stream, 0, 0seek_end );

Return Value

If the call is successful, 0 is returned. If an error exists,-1 is returned. errno stores the error code.

Additional instructions

Unlike lseek (), fseek () returns a read/write location. Therefore, ftell () must be used to obtain the current read/write location.

Example

# Include <stdio. h>
Main ()
{
File * stream;
Long offset;
Fpos_t Pos;
Stream = fopen ("/etc/passwd", "R ");
Fseek (stream, 5, seek_set );
Printf ("offset = % d \ n", ftell (Stream ));
Rewind (Stream );
Fgetpos (stream, & Pos );
Printf ("offset = % d \ n", POS );
Pos = 10;
Fsetpos (stream, & Pos );
Printf ("offset = % d \ n", ftell (Stream ));
Fclose (Stream );
}

Run

Offset = 5
Offset = 0
Offset = 10

Ftell (get the reading location of the file stream)

Related functions

Fseek, rewind, fgetpos, fsetpos

Header file

# Include <stdio. h>

Define functions

Long ftell (File * stream );

Function Description

Ftell () is used to obtain the current read/write location of a file stream. The stream parameter is an opened file pointer.

Return Value

If the call is successful, the current read/write location is returned. If an error occurs,-1 is returned, and errno stores the error code.

Error Code

The file stream of the ebadf parameter is invalid or can be read and written at a movable location.

Example

See fseek ().

Fwrite (write data to a file Stream)

Related functions

Fopen, fread, fseek, fscanf

Header file

# Include <stdio. h>

Define functions

Size_t fwrite (const void * PTR, size_t size, size_t nmemb, file * stream );

Function Description

Fwrite () is used to write data into the file stream. The stream parameter is an opened file pointer. the PTR parameter points to the data address to be written. The total number of characters written is determined by the parameter size * nmemb. Fwrite () returns the number of nmemb actually written.

Return Value

Returns the number of nmemb actually written.

Example

# Include <stdio. h>
# Define set_s (x, y) {strcoy (s [X]. Name, Y); s [X]. size = strlen (y );}
# Define nmemb 3
Struct Test
{
Char name [20];
Int size;
} S [nmemb];
Main ()
{
File * stream;
Set_s (0, "Linux !");
Set_s (1, "FreeBSD !");
Set_s (2, "windows2000 .");
Stream = fopen ("/tmp/fwrite", "W ");
Fwrite (S, sizeof (struct test), nmemb, stream );
Fclose (Stream );
}

Run

See fread ().

GETC (one character read from the file)

Related functions

Read, fopen, fread, fgetc

Header file

# Include <stdio. h>

Define functions

Int GETC (File * stream );

Function Description

GETC () is used to read a character from the file referred to by the parameter stream. If you read the end Of the file without data, the EOF is returned. Although GETC () and fgetc () act the same way, GETC () is defined as a macro and is not a real function call.

Return Value

GETC () returns the read characters. If EOF is returned, it indicates the end of the file.

Example

See fgetc ().

Getchar (reads one character from the standard input device)

Related functions

Fopen, fread, fscanf, GETC

Header file

# Include <stdio. h>

Define functions

Int getchar (void );

Function Description

Getchar () is used to read a character from the standard input device. Convert the character from unsigned char to int and return the result.

Return Value

Getchar () returns the read characters. If EOF is returned, an error occurs.

Additional instructions

Getchar () is not a real function, but is defined by the GETC (stdin) Macro.

Example

# Include <stdio. h>
Main ()
{
File * FP;
Int C, I;
For (I = 0li <5; I ++)
{
C = getchar ();
Putchar (C );
}
}

Run

1234
1234

Gets (reads a string from the standard input device)

Related functions

Fopen, fread, fscanf, fgets

Header file

# Include <stdio. h>

Define functions

Char * gets (char * s );

Function Description

Gets () is used to read characters from the standard device to the memory space specified by parameter S until a line break occurs or the end of the file is read, and then null is added as the string.

Return Value

If gets () is successful, the S pointer is returned. If null is returned, an error occurs.

Additional instructions

Because gets () cannot know the size of string s, it is easy to cause security problems of buffer overflow because it must end the input only when a newline character or the end of the file is encountered. We recommend that you use fgets () instead.

Example

Refer to fgets ()

Mktemp (generate a unique temporary file name)

Related functions

Tmpfile

Header file

# Include <stdlib. h>

Define functions

Char * mktemp (char * template );

Function Description

Mktemp () is used to generate a unique temporary file name. The last six characters in the file name string referred to by the template parameter must be xxxxxx. The generated file name is returned by a string pointer.

Return Value

After the file is successfully opened, the file pointer pointing to the stream will be returned. If the file fails to be opened, null is returned and the error code is stored in errno.

Additional instructions

The file name string referred to by the template parameter must be declared as an array, for example:
Char template [] = "template-xxxxxx ";
Char * template = "template-xxxxxx" is not available ";

Example

# Include <stdlib. h>
Main ()
{
Char template [] = "template-xxxxxx ";
Mktemp (Template );
Printf ("template = % s \ n", template );
}

Putc (write a specified character to the file)

Related functions

Fopen, fwrite, fscanf, fputc

Header file

# Include <stdio. h>

Define functions

Int putc (int c, file * stream );

Function Description

Putc () converts the parameter C to unsignedchar and writes it to the file specified by the parameter stream. Although putc () works the same as fputc (), putc () is defined as a macro and is not a real function call.

Return Value

Putc () returns the successfully written character, that is, the parameter C. If EOF is returned, the write operation fails.

Example

See fputc ().

Putchar (write specified characters to the standard output device)

Related functions

Fopen, fwrite, fscanf, fputc

Header file

# Include <stdio. h>

Define functions

Int putchar (int c );

Function Description

Putchar () is used to write the C character of the parameter to the standard output device.

Return Value

Putchar () returns the output success character, namely the parameter C. If EOF is returned, the output fails.

Additional instructions

Putchar () is not a real function, but is defined by the putc (C, stdout) Macro.

Example

See getchar ().

Rewind (resetting the file stream's read/write position to start with the file)

Related functions

Fseek, ftell, fgetpos, fsetpos

Header file

# Include <stdio. h>

Define functions

Void rewind (File * stream );

Function Description

Rewind () is used to move the read/write location of the file stream to the beginning of the file. The stream parameter is an opened file pointer. This function is equivalent to calling fseek (stream, 0, seek_set ).

Return Value

Example

Refer to fseek ()

Setbuf (set the buffer of the file Stream)

Related functions

Setbuffer, setlinebuf, setvbuf

Header file

# Include <stdio. h>

Define functions

Void setbuf (File * stream, char * BUF );

Function Description

After opening the file stream and reading the content, call setbuf () to set the buffer zone of the file stream. The parameter stream is the specified file stream, and the parameter Buf points to the starting address of the custom buffer. If the Buf parameter is a null pointer, no buffer Io is required. Setbuf () is equivalent to calling: setvbuf (stream, Buf, Buf? _ Iofbf: _ ionbf, bufsiz)

Return Value

Setbuffer (set the buffer of the file Stream)

Related functions

Setlinebuf, setbuf, setvbuf

Header file

# Include <stdio. h>

Define functions

Void setbuffer (File * stream, char * Buf, size_t size );

Function Description

After opening the file stream and reading the content, call setbuffer () to set the buffer zone of the file stream. The parameter stream is the specified file stream. The parameter Buf points to the starting address of the custom buffer. The parameter size is the buffer size.

Return Value

Setlinebuf (set the file stream as a linear buffer)

Related functions

Setbuffer, setbuf, setvbuf

Header file

# Include <stdio. h>

Define functions

Void setlinebuf (File * stream );

Function Description

Setlinebuf () is used to set the no-buffer Io for file streams for behavior. Call: setvbuf (stream, (char *) null, _ iolbf, 0); see setvbuf ().

Return Value

Setvbuf (set the buffer of the file Stream)

Related functions

Setbuffer, setlinebuf, setbuf

Header file

# Include <stdio. h>

Define functions

Int setvbuf (File * stream, char * Buf, int mode, size_t size );

Function Description

After opening the file stream and reading the content, call setvbuf () to set the buffer zone of the file stream. The parameter stream is the specified file stream. The parameter Buf points to the starting address of the custom buffer. The parameter size is the buffer size. The parameter mode has the following types:
_ Ionbf no buffer Io
_ Iolbf no buffer Io Based on Behavior Change
_ Iofbf has no buffer Io at all. If the Buf parameter is a null pointer, no buffer Io is required.

Return Value

Ungetc (write the specified character back to the file Stream)

Related functions

Fputc, getchar, GETC

Header file

# Include <stdio. h>

Define functions

Int ungetc (int c, file * stream );

Function Description

Ungetc () writes the parameter C back to the file stream specified by the parameter stream. This write-back character is obtained by the next function that reads the file stream.

Return Value

If the call succeeds, the return value is a C character. If any error occurs, the return value is EOF.

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