Step 1) Open the file in Read mode. F=open ('guru99.txt', 'r') Step 2) We use the mode function in the code to check that the file is in open mode. If yes, we proceed ahead. If f.mode 'r': Step 3) Use f.read to read file data and store it in variable content for reading files in Python. File Explorer is the new file manager for Windows 8 and Windows 10. It has a newer interface compared to its predecessor, Windows Explorer. 1 X Research source File Explorer lets you manage and view your files, browse network locations, share files with your homegroup, and more. Creates a new File instance by converting the given file: URI into an abstract pathname. The exact form of a file: URI is system-dependent, hence the transformation performed by this constructor is also system-dependent. For a given abstract pathname f it is guaranteed that new File( f.toURI).equals( f.getAbsoluteFile). Creates a new File instance by converting the given file: URI into an abstract pathname. The exact form of a file: URI is system-dependent, hence the transformation performed by this constructor is also system-dependent. For a given abstract pathname f it is guaranteed that new File( f.toURI).equals( f.getAbsoluteFile) so long as the original abstract pathname, the URI, and the new.
Write to an Existing File. To write to an existing file, you must add a parameter to the open function: 'a' - Append - will append to the end of the file 'w' - Write - will overwrite any existing content.
Expand descriptionA reference to an open file on the filesystem.
An instance of a File can be read and/or written depending on what optionsit was opened with. Files also implement Seek to alter the logical cursorthat the file contains internally.
Files are automatically closed when they go out of scope. Errors detectedon closing are ignored by the implementation of Drop. Use the methodsync_all if these errors must be manually handled.
Examples
Creates a new file and write bytes to it (you can also use write()):
Read the contents of a file into a String (you can also use read):
It can be more efficient to read the contents of a file with a bufferedReader. This can be accomplished with BufReader:
Note that, although read and write methods require a &mut File, becauseof the interfaces for Read and Write, the holder of a &File canstill modify the file, either through methods that take &File or byretrieving the underlying OS object and modifying the file that way.Additionally, many operating systems allow concurrent modification of filesby different processes. Avoid assuming that holding a &File means that thefile will not change.
Implementations
impl File
pub fn open>(path: P) -> Result
Attempts to open a file in read-only mode.
See the OpenOptions::open method for more details.
Errors
This function will return an error if path does not already exist.Other errors may also be returned according to OpenOptions::open.
Examples
pub fn create>(path: P) -> Result
Opens a file in write-only mode.
This function will create a file if it does not exist,and will truncate it if it does.
See the OpenOptions::open function for more details.
Examples
pub fn with_options() -> OpenOptions
with_options#65439)Returns a new OpenOptions object.
This function returns a new OpenOptions object that you can use toopen or create a file with specific options if open() or create()are not appropriate.
It is equivalent to OpenOptions::new() but allows you to write morereadable code. Instead of OpenOptions::new().read(true).open('foo.txt')you can write File::with_options().read(true).open('foo.txt'). Thisalso avoids the need to import OpenOptions.
See the OpenOptions::new function for more details.
Examples
pub fn sync_all(&self) -> Result<()>
Attempts to sync all OS-internal metadata to disk.
This function will attempt to ensure that all in-memory data reaches thefilesystem before returning.
This can be used to handle errors that would otherwise only be caughtwhen the File is closed. Dropping a file will ignore errors insynchronizing this in-memory data.
Examples
pub fn sync_data(&self) -> Result<()>
This function is similar to sync_all, except that it might notsynchronize file metadata to the filesystem.
This is intended for use cases that must synchronize content, but don'tneed the metadata on disk. The goal of this method is to reduce diskoperations.
Note that some platforms may simply implement this in terms ofsync_all.
Examples
pub fn set_len(&self, size: u64) -> Result<()>
Truncates or extends the underlying file, updating the size ofthis file to become size.
If the size is less than the current file's size, then the file willbe shrunk. If it is greater than the current file's size, then the filewill be extended to size and have all of the intermediate data filledin with 0s.
The file's cursor isn't changed. In particular, if the cursor was at theend and the file is shrunk using this operation, the cursor will now bepast the end.
Errors
This function will return an error if the file is not opened for writing.Also, std::io::ErrorKind::InvalidInput will be returned if the desiredlength would cause an overflow due to the implementation specifics.
Examples
Note that this method alters the content of the underlying file, eventhough it takes &self rather than &mut self.
pub fn metadata(&self) -> Result
Queries metadata about the underlying file.
Examples
pub fn try_clone(&self) -> Result
Creates a new File instance that shares the same underlying file handleas the existing File instance. Reads, writes, and seeks will affectboth File instances simultaneously.
Examples
Creates two handles for a file named foo.txt:
Assuming there's a file named foo.txt with contents abcdefn, createtwo handles, seek one of them, and read the remaining bytes from theother handle:
pub fn set_permissions(&self, perm: Permissions) -> Result<()>
Changes the permissions on the underlying file.
Platform-specific behavior
This function currently corresponds to the fchmod function on Unix andthe SetFileInformationByHandle function on Windows. Note that, thismay change in the future.
Errors
This function will return an error if the user lacks permission changeattributes on the underlying file. It may also return an error in otheros-specific unspecified cases.
Examples
Note that this method alters the permissions of the underlying file,even though it takes &self rather than &mut self.
Trait Implementations
impl AsFd for File
fn as_fd(&self) -> BorrowedFd<'_>
io_safety#87074)Borrows the file descriptor. Read more
impl AsHandle for File
fn as_handle(&self) -> BorrowedHandle<'_>
io_safety#87074)impl AsRawFd for File
fn as_raw_fd(&self) -> RawFd
Extracts the raw file descriptor. Read more
impl AsRawHandle for File
fn as_raw_handle(&self) -> RawHandle
Extracts the raw handle, without taking any ownership.
impl Debug for File
fn fmt(&self, f: &mut Formatter<'_>) -> Result
Formats the value using the given formatter. Read more
impl FileExt for File
fn read_at(&self, buf: &mut [u8], offset: u64) -> Result
Reads a number of bytes starting from a given offset. Read more
fn write_at(&self, buf: &[u8], offset: u64) -> Result
Writes a number of bytes starting from a given offset. Read more
fn read_exact_at(&self, buf: &mut [u8], offset: u64) -> Result<()>
Reads the exact number of byte required to fill buf from the given offset. Read more
fn write_all_at(&self, buf: &[u8], offset: u64) -> Result<()>
Attempts to write an entire buffer starting from a given offset. Read more
impl FileExt for File
fn read_vectored_at(
&self,
bufs: &mut [IoSliceMut<'_>],
offset: u64
) -> Result
wasi_ext#71213)Reads a number of bytes starting from a given offset. Read more
fn write_vectored_at(&self, bufs: &[IoSlice<'_>], offset: u64) -> Result
wasi_ext#71213)Writes a number of bytes starting from a given offset. Read more
fn tell(&self) -> Result
wasi_ext#71213)Returns the current position within the file. Read more
fn fdstat_set_flags(&self, flags: u16) -> Result<()>
wasi_ext#71213)Adjust the flags associated with this file. Read more
fn fdstat_set_rights(&self, rights: u64, inheriting: u64) -> Result<()>
wasi_ext#71213)Adjust the rights associated with this file. Read more
fn advise(&self, offset: u64, len: u64, advice: u8) -> Result<()>
wasi_ext#71213)Provide file advisory information on a file descriptor. Read more
fn allocate(&self, offset: u64, len: u64) -> Result<()>
wasi_ext#71213)Force the allocation of space in a file. Read more
fn create_directory>(&self, dir: P) -> Result<()>
wasi_ext#71213)fn read_link>(&self, path: P) -> Result
wasi_ext#71213)fn metadata_at>(
&self,
lookup_flags: u32,
path: P
) -> Result
wasi_ext#71213)Return the attributes of a file or directory. Read more
fn remove_file>(&self, path: P) -> Result<()>
wasi_ext#71213)
fn remove_directory>(&self, path: P) -> Result<()>
wasi_ext#71213)fn read_at(&self, buf: &mut [u8], offset: u64) -> Result
wasi_ext#71213)Reads a number of bytes starting from a given offset. Read more
fn read_exact_at(&self, buf: &mut [u8], offset: u64) -> Result<()>
Reads the exact number of byte required to fill buf from the given offset. Read more
fn write_at(&self, buf: &[u8], offset: u64) -> Result
wasi_ext#71213)Writes a number of bytes starting from a given offset. Read more
fn write_all_at(&self, buf: &[u8], offset: u64) -> Result<()>
Attempts to write an entire buffer starting from a given offset. Read more
impl FileExt for File
fn seek_read(&self, buf: &mut [u8], offset: u64) -> Result
Seeks to a given position and reads a number of bytes. Read more
fn seek_write(&self, buf: &[u8], offset: u64) -> Result
Seeks to a given position and writes a number of bytes. Read more
impl From for OwnedHandle
fn from(file: File) -> OwnedHandle
Performs the conversion.
impl From for OwnedFd
fn from(file: File) -> OwnedFd
Performs the conversion.
impl From for Stdio
fn from(file: File) -> Stdio
Converts a File into a Stdio
Examples
File will be converted to Stdio using Stdio::from under the hood.
impl From for File
fn from(owned_fd: OwnedFd) -> Self
Performs the conversion.
impl From for File
fn from(owned: OwnedHandle) -> Self
Performs the conversion.
impl FromRawFd for File
unsafe fn from_raw_fd(fd: RawFd) -> File
Constructs a new instance of Self from the given raw filedescriptor. Read more
impl FromRawHandle for File
unsafe fn from_raw_handle(handle: RawHandle) -> File
Constructs a new I/O object from the specified raw handle. Read more
impl IntoRawFd for File
fn into_raw_fd(self) -> RawFd
Consumes this object, returning the raw underlying file descriptor. Read more
impl IntoRawHandle for File
fn into_raw_handle(self) -> RawHandle
Consumes this object, returning the raw underlying handle. Read more
impl Read for File
fn read(&mut self, buf: &mut [u8]) -> Result
Pull some bytes from this source into the specified buffer, returninghow many bytes were read. Read more
fn read_vectored(&mut self, bufs: &mut [IoSliceMut<'_>]) -> Result
File F New File 2018
Like read, except that it reads into a slice of buffers. Read more
fn is_read_vectored(&self) -> bool
can_vector#69941)Determines if this Reader has an efficient read_vectoredimplementation. Read more
unsafe fn initializer(&self) -> Initializer
read_initializer#42788)Determines if this Reader can work with buffers of uninitializedmemory. Read more
fn read_to_end(&mut self, buf: &mut Vec) -> Result
Read all bytes until EOF in this source, placing them into buf. Read more
fn read_to_string(&mut self, buf: &mut String) -> Result
Read all bytes until EOF in this source, appending them to buf. Read more
fn read_exact(&mut self, buf: &mut [u8]) -> Result<()>
Read the exact number of bytes required to fill buf. Read more
fn by_ref(&mut self) -> &mut Self where
Self: Sized,
Creates a 'by reference' adapter for this instance of Read. Read more
fn bytes(self) -> Byteswhere
Self: Sized,
Transforms this Read instance to an Iterator over its bytes. Read more
fn chain(self, next: R) -> Chainwhere
Self: Sized,
Creates an adapter which will chain this stream with another. Read more
fn take(self, limit: u64) -> Takewhere
Self: Sized,
Creates an adapter which will read at most limit bytes from it. Read more
impl Read for &File
fn read(&mut self, buf: &mut [u8]) -> Result
Pull some bytes from this source into the specified buffer, returninghow many bytes were read. Read more
fn read_vectored(&mut self, bufs: &mut [IoSliceMut<'_>]) -> Result
Like read, except that it reads into a slice of buffers. Read more
fn is_read_vectored(&self) -> bool
can_vector#69941)Determines if this Reader has an efficient read_vectoredimplementation. Read more
unsafe fn initializer(&self) -> Initializer
read_initializer#42788)Determines if this Reader can work with buffers of uninitializedmemory. Read more
fn read_to_end(&mut self, buf: &mut Vec) -> Result
Read all bytes until EOF in this source, placing them into buf. Read more
fn read_to_string(&mut self, buf: &mut String) -> Result
Read all bytes until EOF in this source, appending them to buf. Read more
fn read_exact(&mut self, buf: &mut [u8]) -> Result<()>
Read the exact number of bytes required to fill buf. Read more
fn by_ref(&mut self) -> &mut Self where
Self: Sized,
Creates a 'by reference' adapter for this instance of Read. Read more
fn bytes(self) -> Byteswhere
Self: Sized,
Transforms this Read instance to an Iterator over its bytes. Read more
fn chain(self, next: R) -> Chainwhere
Self: Sized,
Creates an adapter which will chain this stream with another. Read more
fn take(self, limit: u64) -> Takewhere
Self: Sized,
Creates an adapter which will read at most limit bytes from it. Read more
impl Seek for File
fn seek(&mut self, pos: SeekFrom) -> Result
Seek to an offset, in bytes, in a stream. Read more
fn rewind(&mut self) -> Result<()>
Rewind to the beginning of a stream. Read more
fn stream_len(&mut self) -> Result
seek_stream_len#59359)Returns the length of this stream (in bytes). Read more
fn stream_position(&mut self) -> Result
Returns the current seek position from the start of the stream. Read more
impl Seek for &File
fn seek(&mut self, pos: SeekFrom) -> Result
Seek to an offset, in bytes, in a stream. Read more
fn rewind(&mut self) -> Result<()>
Rewind to the beginning of a stream. Read more
fn stream_len(&mut self) -> Result
seek_stream_len#59359)Returns the length of this stream (in bytes). Read more
fn stream_position(&mut self) -> Result
Returns the current seek position from the start of the stream. Read more
impl Write for File
fn write(&mut self, buf: &[u8]) -> Result
Write a buffer into this writer, returning how many bytes were written. Read more
fn write_vectored(&mut self, bufs: &[IoSlice<'_>]) -> Result
Like write, except that it writes from a slice of buffers. Read more
fn is_write_vectored(&self) -> bool
can_vector#69941)Determines if this Writer has an efficient write_vectoredimplementation. Read more
fn flush(&mut self) -> Result<()>
Flush this output stream, ensuring that all intermediately bufferedcontents reach their destination. Read more
fn write_all(&mut self, buf: &[u8]) -> Result<()>
Attempts to write an entire buffer into this writer. Read more
fn write_all_vectored(&mut self, bufs: &mut [IoSlice<'_>]) -> Result<()>
write_all_vectored#70436)Attempts to write multiple buffers into this writer. Read more
fn write_fmt(&mut self, fmt: Arguments<'_>) -> Result<()>
Writes a formatted string into this writer, returning any errorencountered. Read more
fn by_ref(&mut self) -> &mut Self where
Self: Sized,
Creates a 'by reference' adapter for this instance of Write. Read more
impl Write for &File
fn write(&mut self, buf: &[u8]) -> Result
Write a buffer into this writer, returning how many bytes were written. Read more
fn write_vectored(&mut self, bufs: &[IoSlice<'_>]) -> Result
Like write, except that it writes from a slice of buffers. Read more
fn is_write_vectored(&self) -> bool
can_vector#69941)Determines if this Writer has an efficient write_vectoredimplementation. Cook&039 n recipe organizer 12 14 6 quart. Read more
fn flush(&mut self) -> Result<()>
Flush this output stream, ensuring that all intermediately bufferedcontents reach their destination. Read more
fn write_all(&mut self, buf: &[u8]) -> Result<()>
Attempts to write an entire buffer into this writer. Read more
fn write_all_vectored(&mut self, bufs: &mut [IoSlice<'_>]) -> Result<()>
write_all_vectored#70436)Attempts to write multiple buffers into this writer. Read more
fn write_fmt(&mut self, fmt: Arguments<'_>) -> Result<()>
Writes a formatted string into this writer, returning any errorencountered. Read more
fn by_ref(&mut self) -> &mut Self where
Self: Sized,
Creates a 'by reference' adapter for this instance of Write. Read more
Auto Trait Implementations
impl RefUnwindSafe for File
impl Send for File
impl Sync for File
impl Unpin for File
impl UnwindSafe for File
Blanket Implementations
impl Any for T where
T: 'static + ?Sized,
pub fn type_id(&self) -> TypeId
Gets the TypeId of self. Read more
impl Borrow for T where
T: ?Sized,
pub fn borrow(&self) -> &T
Immutably borrows from an owned value. Read more
impl BorrowMut for T where
T: ?Sized,
pub fn borrow_mut(&mut self) -> &mut T
Mutably borrows from an owned value. Read more
impl From for T
pub fn from(t: T) -> T
Performs the conversion.
impl Into for T where
U: From,
pub fn into(self) -> U
Performs the conversion.
impl TryFrom for T where
U: Into,
The type returned in the event of a conversion error.
pub fn try_from(value: U) -> Result>::Error>
Performs the conversion.
impl TryInto for T where
U: TryFrom,
The type returned in the event of a conversion error.
pub fn try_into(self) -> Result>::Error>
Performs the conversion.
C File management
A File can be used to store a large volume of persistent data. Like many other languages ‘C' provides following file management functions,
- Creation of a file
- Opening a file
- Reading a file
- Writing to a file
- Closing a file
Following are the most important file management functions available in ‘C,'
| function | purpose |
|---|---|
| fopen () | Creating a file or opening an existing file |
| fclose () | Closing a file |
| fprintf () | Writing a block of data to a file |
| fscanf () | Reading a block data from a file |
| getc () | Reads a single character from a file |
| putc () | Writes a single character to a file |
| getw () | Reads an integer from a file |
| putw () | Writing an integer to a file |
| fseek () | Sets the position of a file pointer to a specified location |
| ftell () | Returns the current position of a file pointer |
| rewind () | Sets the file pointer at the beginning of a file |
In this tutorial, you will learn-
How to Create a File
Whenever you want to work with a file, the first step is to create a file. A file is nothing but space in a memory where data is stored. App cleaner & uninstaller pro 6 10 plus.
To create a file in a ‘C' program following syntax is used,
In the above syntax, the file is a data structure which is defined in the standard library.
fopen is a standard function which is used to open a file.
- If the file is not present on the system, then it is created and then opened.
- If a file is already present on the system, then it is directly opened using this function.
fp is a file pointer which points to the type file.
Whenever you open or create a file, you have to specify what you are going to do with the file. A file in ‘C' programming can be created or opened for reading/writing purposes. A mode is used to specify whether you want to open a file for any of the below-given purposes. Following are the different types of modes in ‘C' programming which can be used while working with a file.
| File Mode | Description |
|---|---|
| r | Open a file for reading. If a file is in reading mode, then no data is deleted if a file is already present on a system. |
| w | Open a file for writing. If a file is in writing mode, then a new file is created if a file doesn't exist at all. If a file is already present on a system, then all the data inside the file is truncated, and it is opened for writing purposes. |
| a | Open a file in append mode. If a file is in append mode, then the file is opened. The content within the file doesn't change. |
| r+ | open for reading and writing from beginning |
| w+ | open for reading and writing, overwriting a file |
| a+ | open for reading and writing, appending to file |
In the given syntax, the filename and the mode are specified as strings hence they must always be enclosed within double quotes.
Example: Memtest86 5 01 usb installer zip.
Output:
File is created in the same folder where you have saved your code.
You can specify the path where you want to create your file
How to Close a file
One should always close a file whenever the operations on file are over. It means the contents and links to the file are terminated. This prevents accidental damage to the file.
‘C' provides the fclose function to perform file closing operation. The syntax of fclose is as follows,
Example:
The fclose function takes a file pointer as an argument. The file associated with the file pointer is then closed with the help of fclose function. It returns 0 if close was successful and EOF (end of file) if there is an error has occurred while file closing.
After closing the file, the same file pointer can also be used with other files.
In ‘C' programming, files are automatically close when the program is terminated. Closing a file manually by writing fclose function is a good programming practice.
Writing to a File
In C, when you write to a file, newline characters ‘n' must be explicitly added.
The stdio library offers the necessary functions to write to a file:
- fputc(char, file_pointer): It writes a character to the file pointed to by file_pointer.
- fputs(str, file_pointer): It writes a string to the file pointed to by file_pointer.
- fprintf(file_pointer, str, variable_lists): It prints a string to the file pointed to by file_pointer. The string can optionally include format specifiers and a list of variables variable_lists.
The program below shows how to perform writing to a file:
fputc() Function:
Output:
The above program writes a single character into the fputc_test.txt file until it reaches the next line symbol 'n' which indicates that the sentence was successfully written. The process is to take each character of the array and write it into the file.
- In the above program, we have created and opened a file called fputc_test.txt in a write mode and declare our string which will be written into the file.
- We do a character by character write operation using for loop and put each character in our file until the 'n' character is encountered then the file is closed using the fclose function.
fputs () Function:
OUTPUT:
- In the above program, we have created and opened a file called fputs_test.txt in a write mode.
- After we do a write operation using fputs() function by writing three different strings
- Then the file is closed using the fclose function.
fprintf()Function:
OUTPUT:
- In the above program we have created and opened a file called fprintf_test.txt in a write mode.
- After a write operation is performed using fprintf() function by writing a string, then the file is closed using the fclose function.
Reading data from a File
File F New File System
There are three different functions dedicated to reading data from a file
- fgetc(file_pointer): It returns the next character from the file pointed to by the file pointer. When the end of the file has been reached, the EOF is sent back.
- fgets(buffer, n, file_pointer): It reads n-1 characters from the file and stores the string in a buffer in which the NULL character ‘0' is appended as the last character.
- fscanf(file_pointer, conversion_specifiers, variable_adresses): It is used to parse and analyze data. It reads characters from the file and assigns the input to a list of variable pointers variable_adresses using conversion specifiers. Keep in mind that as with scanf, fscanf stops reading a string when space or newline is encountered.
The following program demonstrates reading from fputs_test.txt file using fgets(),fscanf() and fgetc () functions respectively :
Result:
- In the above program, we have opened the file called 'fprintf_test.txt' which was previously written using fprintf() function, and it contains 'Learning C with Guru99' string. We read it using the fgets() function which reads line by line where the buffer size must be enough to handle the entire line.
- We reopen the file to reset the pointer file to point at the beginning of the file. Create various strings variables to handle each word separately. Print the variables to see their contents. The fscanf() is mainly used to extract and parse data from a file.
- Reopen the file to reset the pointer file to point at the beginning of the file. Read data and print it from the file character by character using getc() function until the EOF statement is encountered
- After performing a reading operation file using different variants, we again closed the file using the fclose function.
Interactive File Read and Write with getc and putc
These are the simplest file operations. Getc stands for get character, and putc stands for put character. These two functions are used to handle only a single character at a time.
Following program demonstrates the file handling functions in ‘C' programming:
Output:
- In the above program we have created and opened a file called demo in a write mode.
- After a write operation is performed, then the file is closed using the fclose function.
- We have again opened a file which now contains data in a reading mode. A while loop will execute until the eof is found. Once the end of file is found the operation will be terminated and data will be displayed using printf function.
- After performing a reading operation file is again closed using the fclose function.
File F New File In Java
Summary
- A file is a space in a memory where data is stored.
- ‘C' programming provides various functions to deal with a file.
- A mechanism of manipulating with the files is called as file management.
- A file must be opened before performing operations on it.
- A file can be opened in a read, write or an append mode.
- Getc and putc functions are used to read and write a single character.
- The function fscanf() permits to read and parse data from a file
- We can read (using the getc function) an entire file by looping to cover all the file until the EOF is encountered
- We can write to a file after creating its name, by using the function fprintf() and it must have the newline character at the end of the string text.
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