C语言 如何查找到文件末尾以确定文件大小？
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how to seek to the end of file to determine the file size?
提问by Abhilash Muthuraj
I'm trying to get file size in c programming using seek. I can't use fseek, stat.size nor ftell, there's a custom operating system UNIX in which I need to run.
我正在尝试使用seek在c编程中获取文件大小。我不能使用fseek, stat.size 也不能使用，ftell我需要在其中运行自定义操作系统 UNIX。
How can I find out filesize just by using seek? Is it possible?
如何仅通过使用查找来找出文件大小？是否可以？
FILE *fd = open(argv[1], "r");
if(fd == NULL)
{
printf("Not able to open the file : %s\n", argv[1]);
return;
}
// Set the pointer to the end
seek(fd, 0, SEEK_END);
回答by Nordic Mainframe
seek? You mean lseekprobably. Have a look at the manual page. What does lseekreturn?
seek? 你的意思是lseek大概。看看手册页。什么lseek回报？
回答by alk
If you are just wondering whether the construct using offset = 0with whence = SEEK_ENDwould position the file offset to the end of the file, then "yes" you are right, at least for the "standard f/lseek()"s I came across.
如果您只是想知道使用offset = 0with的构造是否whence = SEEK_END会将文件偏移量定位到文件的末尾，那么“是”您是对的，至少对于f/lseek()我遇到的“标准”。
lseek()should directly return the file offset.
For fseek()a following ftell()will get you the file offset.
lseek()应该直接返回文件偏移量。对于fseek()一个下面ftell()将让你的文件偏移。
回答by Brian McFarland
Normally, open()returns an int, not a FILE *. You have to check for a return value >= 0. fopen()from <stdio.h>returns a FILE *. Also, for the record, fopen()and fseek()are part of the C standard library. A UNIX open() is part of POSIX. So in general, fopen()/ fseek()is more portable.
通常，open()返回一个 int，而不是一个FILE *. 您必须检查返回值 >= 0. fopen()from<stdio.h>返回 a FILE *。另外，为了记录，fopen()并且fseek()是 C 标准库的一部分。UNIX open() 是 POSIX 的一部分。所以总的来说，fopen()/fseek()更便携。
If you are really on a custom "Unix-like" environment, to where that is no longer true (i.e. you have an custom API instead of unistd.h) then you're not going to a good answer here without providing more info. Can you tell us what OS you are really running?
如果您真的在自定义的“类 Unix”环境中，而这不再适用（即您有一个自定义 API 而不是 unistd.h），那么如果不提供更多信息，您将不会在这里得到一个好的答案。你能告诉我们你真正运行的是什么操作系统吗？
Or like Luther suggested, check the return value of lseek()if you are using a normal <unistd.h>.
或者像 Luther 建议的那样，lseek()如果您使用的是普通<unistd.h>.
