fwrite写入文件大小错误的问题

最新推荐文章于 2022-09-20 18:27:41 发布

原创最新推荐文章于 2022-09-20 18:27:41 发布 · 5.1k 阅读

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#fopen #fwrite #wt #wb

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本文探讨了使用fwrite写入文件时遇到字节数与预期不符的问题，并详细解释了fopen函数不同模式（如w与wb）的区别及其对二进制数据写入的影响。

最近使用fwrite将缓冲区的内容写入文件，发现写入的字节数与预期的不一致，后来发现是打开文件时fopen使用的mode是“w”，改为“wb”问题解决。

查看BCB的帮助文档发现:

The mode string used in calls to fopen is one of the following values:

Value	Description
r	Open for reading only.
w	Create for writing. If a file by that name already exists, it will be overwritten.
a	Append; open for writing at end-of-file or create for writing if the file does not exist.
r+	Open an existing file for update (reading and writing).
w+	Create a new file for update (reading and writing). If a file by that name already exists, it will be overwritten.
a+	Open for append; open (or create if the file does not exist) for update at the end of the file.

To specify that a given file is being opened or created in text mode append a t to the mode string (rt, w+t, and so on). Similarly to specify binary mode append ab to the mode string (wb, a+b, and so on).fopen also allows the t or b to be inserted between the letter and the+ character in the mode string; for example rt+ is equivalent tor+t.

If a t or b is not given in the mode string the mode is governed by the global variable_fmode. If _fmode is set to O_BINARY files are opened in binary mode. If_fmode is set to O_TEXT they are opened in text mode. TheseO_... constants are defined in fcntl.h.

原来BCB中fopen的“w”模式默认为“wt”，以文本方式打开文件。

二进制数据中难免有一些特殊字符，以文本方式打开后，fwrite每遇到一个0x0A就会在前面加一个0x0D，造成上面的问题。

Windows以“\r\n”为换行符