【c++基础】判断是否到文件末尾-eof函数

前言

读取文件内容时，需要判断是否到文件末尾，此时用到eof函数。

函数定义

Check whether eofbit is set

Returns true if the eofbit error state flag is set for the stream.

This flag is set by all standard input operations when the End-of-File is reached in the sequence associated with the stream.

Note that the value returned by this function depends on the last operation performed on the stream (and not on the next.

Operations that attempt to read at the End-of-File fail, and thus both the eofbitand the failbitend up set. This function can be used to check whether the failure is due to reaching the End-of-File or to some other reason.

#include <fstream>
std::ios::eof
bool eof() const;

代码实例

// ios::eof example
#include <iostream>     // std::cout
#include <fstream>      // std::ifstream

int main () 
{ 
    std::ifstream is("example.txt");   // open file
    char c;
    while (is.get(c))                  // loop getting single characters
        std::cout << c;

    if (is.eof())                      // check for EOF
        std::cout << "[EoF reached]\n";
    else
        std::cout << "[error reading]\n";
    is.close();                        // close file
    return 0;
}

问题

何时说明到达末尾呢？

通过测试代码发现，读取文件内容之后再检测是否达到文件末尾。

测试代码

        while (!in_txt.eof())
        {
            if (in_txt.eof()) std::cout << "[EOF reached in while]" << std::endl;
            getline(in_txt, inputName);
            if (in_txt.eof()) std::cout << "[EOF reached after while]" << std::endl;
            dir = dir1 + inputName;
            dir += ".jpg";
            std::cout << dir << std::endl;
        }

测试输出

..//FDDB-originalPics//2002/08/07/big/img_1453.jpg
..//FDDB-originalPics//2002/08/02/big/img_760.jpg
[EOF reached after while]
..//FDDB-originalPics//.jpg
[EOF reached]
1: 1
02
..//FDDB-originalPics//2002/07/28/big/img_416.jpg

参考

1.cplusplus.com;

完