Learn php's fwrite function

This article introduces the usage of PHP’s fwrite function for your reference.

PHP fwrite() The fwrite() function is used to write a string to a file and returns the number of characters written successfully, otherwise it returns FALSE.

Syntax: int fwrite( resource handle, string string [, int length] ) fwrite() writes the contents of string to the file pointer handle. Parameter Description: Parameter Description handle The file pointer to which the string is to be written, usually created by the fopen() function data string to write length is optional and specifies the maximum number of bytes to be written

If the optional parameter length is specified, writing will stop when length bytes have been written or the string has been written.

Example:

$fh = fopen($filename, "w"); echo fwrite($fh, $word); // Output: 6 fclose($fh); ?>

Execute the example program. In the same directory as the program, the content of the file.txt file is: Hello!

Use length parameter In the above example, if the length parameter is used, at most length strings will be written: echo fwrite($fh, $word, 4); // Output: 4

PHP fwrite append writing The additional writing to the file actually has nothing to do with the fwrite function, but with the mode in which the fopen function opens the file. When fopen opens a file and the mode parameter selects a , it means appending to the file:

$fh = fopen($filename, "a"); echo fwrite($fh, $word); fclose($fh); ?>

PHP fwrite newline writing If you want to implement newline writing in the file, you only need to add the newline character n where the newline is required in the written content:

$fh = fopen($filename, "a"); echo fwrite($fh, $word); fclose($fh); ?>

The above example adds n newlines at the end of the content. To make n represent a newline when writing a file, you need to use double quotes when writing (as in the example above). If you use single quotes, the n character will not be interpreted as a newline but as an n string. Click to view: PHP string The difference between single quotes and double quotes.

n is already a real line feed. If you want to simulate a carriage return and line feed on the Windows operating system (that is, when you open a file with WordPad, it is not a black square but a list of lines), you can add r before n and carriage return. symbol:

PHP fwrite write permission When opening an existing file (usually in append-write mode), it is necessary to check whether the file has write permissions to avoid a system error. Use the is_writable function to check whether the file is writable.

The following is an example of stricter checking in append writing mode:

// Make sure the file exists and is writable if (is_writable($filename)) { //open a file if (!$fh = fopen($filename, 'a')) { echo "Cannot open file $filename"; exit; } // write content if (fwrite($fh, $word) === FALSE) { echo "Cannot write to file $filename"; exit; } echo "Successfully written $word to file $filename"; fclose($fh); } else { echo "File $filename is not writable"; } ?>

PHP fwrite function just performs the action of writing a string to a file. Its actual behavior depends more on the fopen function. If you want to write or append a string to a file all at once, the file_put_contents function may be a better choice.

PHP file_put_contents function: write or append string to file The PHP file_put_contents() function is the most suitable choice for writing a string or appending string contents to a file in one go.

file_put_contents() The file_put_contents() function is used to write a string to a file. It returns the number of bytes of data written to the file successfully, and returns FALSE if it fails.

Syntax: int file_put_contents ( string filename, string data [, int flags [, resource context]] )

Parameter Description: Parameter Description filename The name of the file to write data to data The data to be written. The type can be string, array (but not multi-dimensional array), or stream resource flags are optional and specify how to open/write the file. Possible values: FILE_USE_INCLUDE_PATH: Check the built-in path for a copy of filename FILE_APPEND: Write data by appending to the end of the file LOCK_EX: lock the file context is optional. Context is a set of options through which text attributes can be modified

Example:

Run this example, the browser output: 18 The content of the test.txt file (in the same directory as the program) is: This is something.

Tips If the file does not exist, create the file, equivalent to the behavior of the fopen() function. If the file exists, the contents of the file will be cleared by default. You can set the flags parameter value to FILE_APPEND to avoid this (see below). This function is safe for use with binary objects.

Write content in append form When the flags parameter value is set to FILE_APPEND, it means writing new data by appending content after the existing file content: After executing the program, the content of the test.txt file becomes: This is something.This is another something. The behavior of file_put_contents() is actually the same as calling fopen(), fwrite() and fclose() in sequence.

Reference reading

PHP fopen: file creation and opening. PHP fwrite: Write a string to a file. PHP close: Close an open file. PHP file_get_contents: Read the entire file contents into a string. PHP checks whether the file can be read and written using is_readable, is_writable and is_executable functions

The is_readable() function is used to check whether the file is readable, the is_writable() function is used to check whether the file is writable, and the is_executable() function is used to check whether the file is executable. is_readable() The is_readable() function is used to check whether the file is readable. If the specified file or directory exists and is readable, it returns TRUE, otherwise it returns FALSE.

Syntax: bool is_readable(string filename) example:

is_writable() The is_writable() function is used to check whether the file is writable and returns TRUE if the file exists and is writable, otherwise it returns FALSE.

Syntax: bool is_writable(string filename) The filename parameter can be a directory name that allows writability checking.

Example:

is_executable() The is_executable() function is used to check whether the file is executable and returns TRUE if the file exists and is executable, otherwise it returns FALSE. For usage, please refer to is_writable().