prePEND文本在C文件 [英] Prepend text to a file in C

问题描述

我想用C，这些文件可能会相当大一个标准的头添加到一个文件（或文件组），所以这将是一个坏主意，它们加载到内存中，或将它们复制到临时文件（我想）。

有没有简单地prePEND直接头到每一个文件的方式？

头本身是相当小的，不超过1 KB

解决方案

应该可以不用临时文件 - 你可以阅读从最终的文件，逐块，在写每个块回（original_position + header_size）。第一块将被写回 header_size ，留有余地头。

不过，你真的不希望这样做。这将损坏的文件，如果中止（想：磁盘空间，其他I / O错误，掉电，等等）。

因此​​，你实际上应该使用临时文件 - 写它你需要的一切，然后将其重命名为原来的文件名（假设你创建相同的文件系统上的临时文件，否则你需要复制）

编辑：澄清我的意思，简化的解决方案时，整个文件在RAM适合：

• 分配缓冲区大小相同的文件


• 打开文件，并读入缓冲区


• 求（文件，header_size），并写在这里的缓冲


• 求（文件，0）写的标题

如果该文件是为大，你可以分配较小的缓冲区，并重复读/写在开始读FILE_SIZE - BUFFER_SIZE 和 FILE_SIZE写 - BUFFER_SIZE + header_size 。 2 * BUFFER_SIZE ，写在 FILE_SIZE - - 2 * BUFFER_SIZE + header_size ，然后在读下一大块FILE_SIZE重复等等。

不过，让我再说一遍：！你就有可能破坏你的文件，如果它失败

I want to add a standard header to a file (or group of files) using C. These files could be quite large, so it would be a bad idea to load them into memory, or copy them into temporary files (I think).

Is there a way to simply prepend the header directly to each file?

The header itself is quite small, not more than 1 KB

解决方案

It should be possible without a temporary file - you can read the file from the end, block by block, writing each block back at (original_position + header_size). The first block would be written back at header_size, leaving room for the header.

However, you don't really want to do this. It would corrupt the file if aborted (think: out of disk space, other I/O error, power down, whatever).

Thus, you should actually use temporary file - write to it everything you need, then rename it to the original file's name (assuming you create temporary file on the same file system, otherwise you'd need to copy).

Edit: to clarify what I mean, simplified solution when the whole file fits in RAM:

• allocate buffer same size as the file
• open the file, and read it into the buffer
• seek(file, header_size) and write the buffer here
• seek(file, 0) write the header

If the file is to big, you can allocate smaller buffer and repeat reads/writes starting with read at file_size - buffer_size and write at file_size - buffer_size + header_size. Then repeat with next chunk read at file_size - 2 * buffer_size, write at file_size - 2 * buffer_size + header_size, and so on.

But let me repeat: you risk corrupting your file if it fails!

这篇关于prePEND文本在C文件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！