如何找到文件的结尾 [英] How to find an end of file
问题描述
在阅读
a文件时找到文件结束条件的正确方法是什么？
feof（）如何检测文件末尾是到达了吗？
这是否需要操作系统的支持？
提前获得任何帮助...
" junky_fellow" <菊********** @ yahoo.co.in>在消息中写道
新闻：8c ************************* @ posting.google.co m ... < blockquote class =post_quotes>在读取文件时找到文件结束条件的正确方法是什么？
feof（）如何检测到文件结尾？
feof（）未检测到文件结束，它报告在上一次读取操作期间达到了文件结尾
。
这是否需要操作系统的支持？
如果文件是用OS实现的，feof（）将依赖OS报告这样的
读取操作的
a条件。
如果文件在C库中实现，操作系统不是问题。
重要的是要注意feof（）是违反直觉的：
- 是否达到文件末尾的读操作设置条件是
未指定：fgets（）读取最后一行将可能没有设置它，而
fscanf（）吃掉尾随空格可能。
- 如果文件是由另一个函数写入的（或者进程在哪里创建
sense），feof（）可能会返回非0，即使有更多数据可用于
读取（阅读前可能需要clearerr（）或fseek（））。
根据经验，在读取操作失败后，只使用feof（）消除文件结尾的读取错误
。
成语，例如while（！feof（f））{...}和do {...} while（！feof（f））;是b
bogus，必须避免。
-
Chqrlie。
PS：我知道7.19.6.2示例3节19节。这段代码snipplet是伪造的，而b
无用。无论如何，AAMOF大多数do / while循环都是假的。
junky_fellow写道：在阅读时找到文件结束条件的正确方法是什么
一个文件？
feof（）如何检测到文件末尾？
这是否需要OS的支持？
你可以自己做，没有feof（），通过做
struct stat statstruct;
stat（" filename"，& statstruct）;
statstruct.st_size是文件中的字节数。
提前填写任何帮助...
使用feof（）更容易。
FILE * fp = fopen（... ）;
while（！feof（fp））{
...读取的东西
}
>使用feof（）更容易。
FILE * fp = fopen（...）;
while（！feof（fp））{
...读取东西
}
当然，正如之前的海报所说，你可能有一个简短的数字或
甚至是一个错误，所以考虑到这一点。
while（！feof（fp））{
/ *短计数？ * /
n = fread（buffer，...，fp）;
if（n！= whatever）{
if（ferror（））
...某种错误
if（feof（））
...文件结尾
}
}
What is the proper way of finding an end of file condition while reading
a file ?
How does feof() detects that end of file is reached ?
Does this require support from OS ?
Thanx in advance for any help ...
"junky_fellow" <ju**********@yahoo.co.in> wrote in message
news:8c*************************@posting.google.co m...What is the proper way of finding an end of file condition while reading
a file ?
How does feof() detects that end of file is reached ?
feof() does not detect that end of file is reached, it reports that end of file
was reached during a previous read operation.
Does this require support from OS ?
if files are implemented with the OS, feof() will rely on the OS reporting such
a condition for read operations.
if files are implemented within the C library, the OS is not an issue.
It is important to notice that feof() is counterintuitive:
- Whether a read operation that reaches the end of a file set the condition is
not specified : fgets() reading the last line will probably not set it, while
fscanf() eating trailing white space might.
- If the file is being written by another function (or process where that makes
sense), feof() may return non 0 even after more data becomes available for
reading (clearerr() or fseek() may be needed before reading).
As a rule of thumb, only use feof() to disambiguate end of file from read error
after a read operation fails.
Idioms such as while (!feof(f)) { ... } and do { ... } while (!feof(f)); are
bogus and must be avoided.
--
Chqrlie.
PS: I know about 7.19.6.2 example 3 verse 19. This code snipplet is bogus and
useless. AAMOF most do/while loops are bogus anyway.
junky_fellow wrote:What is the proper way of finding an end of file condition while reading
a file ?
How does feof() detects that end of file is reached ?
Does this require support from OS ?
You can do it yourself without feof(), by doing
struct stat statstruct;
stat("filename", &statstruct);
statstruct.st_size is the number of bytes in the file.
Thanx in advance for any help ...
Using feof() is easier though.
FILE *fp = fopen(...);
while (!feof(fp)) {
... read stuff
}
> Using feof() is easier though.
FILE *fp = fopen(...);
while (!feof(fp)) {
... read stuff
}
And of course as the previous poster said, you may have a short count or
even an error, so take that into account.
while (!feof(fp)) {
/* Short count ? */
n = fread(buffer, ..., fp);
if (n != whatever) {
if (ferror())
... some kind of error
if (feof())
... end of file
}
}
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