碳二元文件：截断或以修改其结束调整 [英] C binary file : truncate or resize in order to modify its end

问题描述

我有一个 FILE *文件保存一些二进制数据。比方说，这个数据是双列表和最后一个项目是描述那些是什么双重的字符串。我想修改这个字符串（新的字符串可能更短）。首先，我删除旧的字符串。我需要查找的字符串的起点：

I have a FILE* file that holds some binary data. Let's say that this data are a list of double and that the last entry is a string that describes what are those double. I want to modify this string (the new string might be shorter). So first i delete the old string. I need to find the starting point of the string :

fseek(file,-size(sring.size()),SEEK_END);

和那我应该怎么办？我发现删除文件环节结束，但我不知道该用哪一个？一旦文件被重新大小，可以用我简单地写我的新字符串 FWRITE ？

and then what should i do ? i found Delete End of File link but i don't know which one to use... Once the file is re-sized, can i simply write my new string using fwrite ?

推荐答案

如果您要调整的文件，那么 ftruncate（）（ http://www.linuxmanpages.com/man2/ftruncate.2.php ）是你的功能寻找。你需要调用的fileno（）在 FILE * 结构来获取<$ C $文件描述符C> ftruncate（），虽然

If you want to resize a file, then ftruncate() (http://www.linuxmanpages.com/man2/ftruncate.2.php) is the function you're looking for. You'll need to call fileno() on the FILE * structure to get the file descriptor for ftruncate(), though.

至于追加新的数据（新的字符串）一旦文件大小减少，只是寻求结束（ fseek的（文件，0，SEEK_END） ）和的fwrite（）ING也应该这样做。

As for appending the new data (the new string) once the file has been reduced in size, just seeking to the end (fseek(file, 0, SEEK_END)) and fwrite()'ing there should do it.

编辑：记得打电话 fflush（）截断文件之前

remember to call fflush() before truncating the file!

这篇关于碳二元文件：截断或以修改其结束调整的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！