The stream is positioned at the end of the file. Subsequent writes to the file will always end up at the then cur- rent end of file, irrespective of any intervening fseek 3 or similar. Stack Overflow for Teams — Collaborate and share knowledge with a private group.
Create a free Team What is Teams? Collectives on Stack Overflow. Learn more. Append to the end of a file in C Ask Question. Asked 8 years, 3 months ago. Active 8 years, 3 months ago. Viewed k times. Sonofblip Sonofblip 1, 2 2 gold badges 11 11 silver badges 19 19 bronze badges. Use 0 for the offset and it ought to work.
The second parameter of the open function is the mode , a string with one character. That single character basically tells Python what you are planning to do with the file in your program.
To use text or binary mode, you would need to add these characters to the main mode. For example: "wb" means writing in binary mode. It really makes sense for Python to grant only certain permissions based what you are planning to do with the file, right? Why should Python allow your program to do more than necessary?
This is basically why modes exist. Think about it — allowing a program to do more than necessary can problematic. For example, if you only need to read the content of a file, it can be dangerous to allow your program to modify it unexpectedly, which could potentially introduce bugs.
Now that you know more about the arguments that the open function takes, let's see how you can open a file and store it in a variable to use it in your program. I know you might be asking: what type of value is returned by open?
According to the Python Documentation , a file object is:. This is basically telling us that a file object is an object that lets us work and interact with existing files in our Python program. For us to be able to work file objects, we need to have a way to "interact" with them in our program and that is exactly what methods do. Let's see some of them. The first method that you need to learn about is read , which returns the entire content of the file as a string.
You can use the type function to confirm that the value returned by f. In this case, the entire file was printed because we did not specify a maximum number of bytes, but we can do this as well. To do this, you need to call the close method, like this:. You can read a file line by line with these two methods. They are slightly different, so let's see them in detail. In contrast, readlines returns a list with all the lines of the file as individual elements strings.
This is the syntax:. If you need to create a file "dynamically" using Python, you can do it with the "x" mode. With this mode, you can create a file and then write to it dynamically using methods that you will learn in just a few moments.
A curious thing is that if you try to run this line again and a file with that name already exists, you will see this error:. According to the Python Documentation , this exception runtime error is:.
To modify write to a file, you need to use the write method. You have two ways to do it append or write based on the mode that you choose to open it with. Let's see them in detail. The "a" mode allows you to open a file to append some content to it. And we want to add a new line to it, we can open it using the "a" mode append and then, call the write method, passing the content that we want to append as argument. This is the basic syntax to call the write method:. Sometimes, you may want to delete the content of a file and replace it entirely with new content.
You can do this with the write method if you open the file with the "w" mode. As you can see, opening a file with the "w" mode and then writing to it replaces the existing content. If you want to write several lines at once, you can use the writelines method, which takes a list of strings. This method is equivalent to the StreamWriter String, Boolean constructor overload.
If the file specified by path does not exist, it is created. If the file does exist, write operations to the StreamWriter append text to the file. Additional threads are permitted to read the file while it is open. The path parameter is permitted to specify relative or absolute path information.
Relative path information is interpreted as relative to the current working directory. To obtain the current working directory, see GetCurrentDirectory. The SreamWriter. WriteLine method writes a whole line in C.
We can initialize an object of the StreamWriter class with the File. AppendText method to initialize an instance of StreamWriter class that would append the data to the file.
0コメント