PHP file read operations involve more PHP file operation functions than file write operations. These functions will be introduced in detail in the code example.
The three main steps and some file operation functions involved in reading data stored in text files are as follows:
1. Open the file (file operation function: fopen)
2. File data reading (file operation functions: fgets, file, readfile, feof, etc.)
3. Close the file (file operation function: fclose)
The following is still using the PHP file read and write operation code example to explain the specific application of file reading method. In the example, by calling different PHP file read operation functions to read data in text files, you can deepen the understanding of PHP file read operation functions so that it can be used reasonably in PHP website development. The data written in the text file comes from the file writing tutorial for PHP file reading and writing operations. You can also refer to this article about the file reading and writing mode in the fopen function.
PHP file reading operation code example
<?
$readFun = "fread";
switch ($readFun)
{
case "fgetss":
@$fp = fopen("","r") or die("system error");
$allowable_tags = "<h1>";
while (!feof($fp)) {
$output = fgetss($fp,100,$allowable_tags);
echo $output;
}
fclose($fp);
break;
case "fgetcsv":
@$fp = fopen("","r") or die("system error");
while (!feof($fp)) {
$output = fgetcsv($fp,100,"\t");
print_r($output);
}
fclose($fp);
break;
case "readfile":
echo readfile("");
break;
case "fpassthru":
@$fp = fopen("","r") or die("system error");
if(!fpassthru($fp))
exit();
fclose($fp);
break;
case "file":
$output = file("");
print_r($output);
break;
case "fgetc":
@$fp = fopen("","r") or die("system error");
while (!feof($fp)) {
$str = fgetc($fp);
echo ($str == "\n"?"<br/>":$str);
}
fclose($fp);
break;
case "fread":
@$fp = fopen("","r") or die("system error");
echo fread($fp,300);
fclose($fp);
break;
default:
@$fp = fopen("","r") or die("system error");
while (!feof($fp)) {
$output = fgets($fp,100);
echo $output;
}
fclose($fp);
break;
}
?>
Note: In the above example, you can implement calls to different PHP file reading methods by assigning $readFun. The PHP file reading operation functions involved include fgets, fgetss, fgetcsv, readfile, fpassthru, file, fgetc and other functions.
The difference between PHP file read operation functions fgets, fgetss, fgetcsv
In the code instance, the default PHP file read operation function is fgets, and the functions of fgetss and fgetcsv functions are the same as fgets, and they read one line in the file at a time until the end of the file. Here I set the data length in the read text file to be 100, that is, the maximum read length is 99 (100-1). In this way, when a newline character \n or file ending character EOF is encountered, or 99 bytes are read from the file, it stops reading the data. The fgets function returns the data read by the file, in a string type.
The fgetss function is a variant of the fgets function. It can strip away PHP and HTML tags and filter unnecessary data by passing the third parameter, which can improve website security. For example, the user's input data can be filtered in the message book. The prototype of the fgetss function is as follows:
string fgetss(resource fp,int length, string[optional] allowable_tags)
The allowable_tags parameter is an optional. In the example, I wrote a line of text containing html, body, and h1 tags in the file in advance, and then in the code I set that only h1 tags can appear.
The fgetcsv function is another variant of fgets. The difference is that when the data written in your text file uses a delimiter, you can use fgetcsv to decompose a line into multiple lines, and the returned result is stored in an array. The function prototype is as follows:
array fgetcsv(resource fp,int length, string[optional] delimiter,string[optional] enclosure)
Delimiter is optional. Since I used \t in the data I wrote to the file before, I used \t in the file reading function fgetcsv in the instance, and then printed out the array structure returned by fgetcsv through print_r.
The common feature of the three PHP file reading operations functions fgets, fgetss, and fgetcsv is that they all need to use the fopen function to open the read file in advance, and at the same time, they use the feof function to determine whether the file pointer reaches the end of the file. Remember to use the fclose function to close the file after the read operation is completed.
fgetc: Read a single character
The fgetc function is used to read a character. In the code example, I read characters one by one. When I encounter \n characters, it is converted into a br mark in the html file to display the specific line break effect in the browser. Of course, the efficiency of this function is definitely relatively low and it is not recommended to use it.
The difference between PHP file read operation functions readfile, fpassthru, and file
The common thing among the three functions is that they can read the entire file at once, rather than reading one line or one character at a time. The difference is:
The readfile function opens the file and returns the file content and outputs it directly on the browser. Like the fopen function, the function returns the total number of characters in the file. The second parameter of the readfile function is an option, indicating whether PHP should look for files in include_path. In the code example, I use the echo statement not to output the read file content, but to output the total number of read file characters. The read file content readfile function has been automatically output, which must be clear! The prototype of the readfile function is as follows:
int readfile(string filename,int[optional] use_include_path)
The file function is another way to read a file. It sends the read file contents into an array, with an array unit per line. The file function prototype is as follows:
array file(string filename,bool[optional] use_include_path)
The fpassthru() function is used to output all remaining data at the file pointer, that is, if the file pointer is not at the beginning, it only outputs the data behind the file pointer. This function reads the given file pointer to EOF from the current position and writes the result to the output buffer, with the return value as the number of characters output. Returns FALSE when an error occurs. Compared with the readfile() function, the fpassthru() function needs to open the file first and close the file after data is read.
fread, file_exists, filesize functions
The fread function is also a way to read a file. It can read any byte from the file, either satisfying the length or reading to the end of the file. The prototype of the read function is as follows:
string fread(resource fp,int length)
When using the fread function, when you want to read all the data of the file but don't know the length of the file data, the filesize function can solve this problem, i.e.
<?
@$fp = fopen("","r") or die("system error");
echo fread($fp,filesize(""));
fclose($fp);
?>
In the PHP file read and write operation tutorial, we have not used the file_exists function. Usually in PHP website development, for various reasons, sometimes when the file does not exist, we are not like creating a new file. At this time, we need to use the file_exists function to determine whether the file exists before using the fopen function, that is,
<?
if(file_exists(""))
{
//Perform PHP file reading and writing operations}
?>
The above introduces various methods of PHP reading and writing operation functions. By rationally applying PHP file read and write operation functions, simple message books, website log records and other functions can be realized.