C ++中istream的效果 [英] eof of istream in C++

问题描述

bool ios::eof ( ) const;

根据库，

如果eofbit流的错误标志已由先前的I / O操作设置为
，则该函数返回true。当按与流关联的序列
到达文件末尾时，所有标准
输入操作均会设置此标志。

The function returns true if the eofbit stream's error flag has been set by a previous i/o operation. This flag is set by all standard input operations when the End Of File is reached in the sequence associated with the stream.

我编写了一个程序来运行一些测试：

I wrote a program to run some tests:

int main(int argc, char *argv[])
{
    ifstream ifs(argv[1]);
    float f;
    ifs >> f;

    cout << ifs.eof() << endl; //check if eofbit set

    ifs.close();
}

我测试了2个文件，testcase1.txt和testcase2.txt。

I tested 2 files, testcase1.txt and testcase2.txt.

testcase1.txt是在终端中使用 cat 生成的，[Ctrl-D]用于结束输入：

testcase1.txt was generated in the terminal with cat, [Ctrl-D] was used to end input:

[~/C++ $] cat > testcase1.txt
1.234[Ctrl-D]

testcase2.txt是在 vim ，我打开 vim 并输入 1.234 ，然后保存并退出。

testcase2.txt was generated in vim, I opened up vim and just inputted 1.234, and then saved and exited.

测试结果

测试结果为 testcase1.txt 是 1 ，表示已设置 eofbit ，

Test result with testcase1.txt is 1, which means the eofbit is set,

[~/C++ $] ./a.out testcase1.txt
1

带有 testcase2.txt 的测试结果为 0 ，

[~/C++ $] ./a.out testcase2.txt
0

我同时打开 testcase1.txt 和 testcase2.txt 在 vim 中，它们看起来完全一样，然后为什么 eofbit testcase2.txt 设置c>？

I open both testcase1.txt and testcase2.txt in vim, they look exactly the same, then why the eofbit wasn't set for testcase2.txt?

推荐答案

您会在评论中看到一行新的内容：

As you see in comment, there is a new line:

ifstream ifs(argv[1]);
float f;
ifs >> f;
char c;
ifs.get( c ); // this will get '\n'

即使如此， EOF 仍然不会设置。...阅读您再次引用的段落：

Even so, the EOF still won't set.... Read the paragraph you quoted again:

如果eofbit流的错误标志已由先前的I / O操作设置为
。当按与流关联的序列
到达文件末尾时，所有标准
输入操作均会设置此标志。

The function returns true if the eofbit stream's error flag has been set by a previous i/o operation. This flag is set by all standard input operations when the End Of File is reached in the sequence associated with the stream.

要设置 eof 位，必须读取PASS的eof。您可以根据需要使用 peek（）进行操作。

To get the eof bit set, you have to read PASS the eof. You can use peek() to do it if you want.

ifstream ifs(argv[1]);
float f;
ifs >> f;
char c;
ifs.get( c ); // this will get '\n'
ifs.eof();  // this is false;
ifs.peek();
ifs.eof(); // this is true

另请参见： istream :: peek好奇行为举报。 EOF

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