如何从头到中间读取文件

How to read a file from the begining to the middle

本文关键字：中间 读取 文件      更新时间：2023-10-16

所以我从头到尾读了几行。还行。但现在我的目的是从头到中阅读。我的文件包含浮点数，如下所示。我想如果我计算文件的长度，我会把它放在一个循环中，然后读成filelenghth/2。但我不能，因为每一行都是 6 位的输入空间和数字可以 change.it 现在不是一个好的编程实践根据数据计算。

1.33
5.45
6.21
2.48
3.84
7.96
8.14
4.36
2.24
9.45

我需要比以下代码更有效的解决方案。为此，您建议什么样的解决方案。

fstream inputNumbersFile("input.txt");
ifstream lengthOfNumbersFile("input.txt"); // for getting size of file
lengthOfNumbersFile.seekg(0, lengthOfNumbersFile.end);
int lengthFile = lengthOfNumbersFile.tellg();;
if (inputNumbersFile.is_open())
{
    for (int i = 0; i < lengthFile;)
    {
        while (getline(inputNumbersFile, line))
        {               
            cout << line << endl;
            i = i + 6;
            if (i == lengthFile/2)
            {
                break;
            }
        }
    }       
}

您可以执行以下操作：

#include <string>
#include <fstream>
#include <stdexcept>
#include <iostream>
using std::string;
using std::ifstream;
using std::ios_base;
using std::ios;
using std::invalid_argument;
using std::getline;
using std::cout;
using std::cerr;
using std::endl;

static string file_str(const string & path)
{
    ifstream ifs(&path[0], ios_base::in | ios_base::binary);
    if (!ifs)
        throw invalid_argument("File: " + path + " not found!");
    // Enable exceptions
    ifs.exceptions();
    // Init string buffer to hold file data.
    string buffer;
    // Set ifs input position indicator to end.
    ifs.seekg(0, ios::end);
    // Set the buffer capacity to exactly half the file contents size.
    buffer.resize(ifs.tellg() / 2);
    // Set ifs input position indicator to beginning.
    ifs.seekg(0);
    string::size_type buffer_size(buffer.size());
    // Read file contents into string buffer.
    ifs.read(&buffer[0], buffer_size);
    if (buffer[buffer_size - 1] != 'n')
    {
        // Continue reading until we find the next newline.
        string remaining;
        getline(ifs, remaining);
        // Append to buffer.
        buffer += remaining + 'n';
    }
    ifs.close();
    // Return by RVO.
    return buffer;
}

int main(int argc, const char * argv[])
{
    try
    {
        string file_contents = file_str(R"(C:Users...DesktopMyTextFile.txt)");
        cout << file_contents << endl;
    }
    catch (string message)
    {
        cerr << message << endl;
        return 1;
    }
    return 0;
}

其中，带有以下奇数换行符的文本文件：

line one
line two
line three
line four
line five

将改为：

"line onernline twornline threern"

并使用以下偶数换行文本文件：

line one
line two
line three
line four
line five
line six

将改为：

"line onernline twornline threern"
相关文章：