Questions and Answers on PHP File Operation_PHP Tutorial

Q&A on PHP file operations
Preface:
PHP supports the operation of various databases, and also has rich operating methods for file operations. Many friends’ current operations are still based on file operations, but sometimes There are still a lot of confusions and doubts when operating files. The following is a collection of some problems about file operations that I encountered in my daily writing process and that my friends on the forum encountered.
Q: How to create a new file?
Answer:
1. Use fopen("File name to be created", "Parameter"), the parameters can be w, w+, a, a+
2. Use exec("echo '' > The file name to be created"); This is to use the system method to create the file. You can also use the touch Linux command to create
Q: Why can't I create the file?
Answer:
1. If you use fopen to create a file, do you use the parameters correctly?
2. For system permission issues, please ask your WEBMASTER whether your FTP directory has write permissions
3. FTP permission problem. You need to confirm that the directory where the file where your PHP file is to be written must have write permission. That is, the other group must have write permission after logging in to your FTP software.
If not, please modify the permission and try again.
Q: How to read a file into an array?
Answer: Use the file function
Q: How to read out all the files?
Answer:
1. Use fread($fp);
2. If your PHP version >= 4.3.0, you can use file_get_contents();
Q: How to determine whether the file exists ?
Answer: Use file_exists();
Ask again: Why not use fopen() to judge?
Answer: The reason is that sometimes the data returned by fopen leads us to wrong judgments due to permission issues.
Q: Why do I get an error when I read a WEB page?
Answer:
1. It may be that your transmission parameters are wrong. When reading a WEB page, you can only use r mode to read the page
2. Make sure that the WEB page you want to read is accessible
Q: How can I get the relevant attributes of a file?
Answer: PHP provides a set of methods to obtain file attributes, such as filemtime(), fileowner(), filegroup(), filectime(), fileatime()... Please refer to the manual for detailed usage.
Q: After opening a file in PHP, can I position the file "cursor" like C?
A: Yes, use fseek();
Q: I want to not allow others to access the file when accessing it, what should I do?
Answer:
1. You can use other programs to restrict users from accessing the page for file operations
2. Use flock(); for detailed parameters and usage, please refer to the manual
Q: How to delete The first line in the file, or specify a line of data?
Answer:
PHP does not provide such an operation method, but we can use it in combination. The following code demonstrates that we will delete the third line of data in the file "test.dat" (the data in the test.dat file is more than Three lines)