Question

所以我从头到尾读了一行。没关系。但现在我的目的是从头到尾阅读。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，我会把它放在循环中并将其读作filelenghth/2。但我不能，因为每行都是6位的输入空格，数字可以改变。现在不是根据数据计算好的编程习惯。

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。你为此目的建议了什么样的解决方案。

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;
            }
        }
    }       
}

Answer 1

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\...\Desktop\MyTextFile.txt)");
        cout << file_contents << endl;
    }
    catch (string message)
    {
        cerr << message << endl;
        return 1;
    }
    return 0;
}

其中，使用以下奇数换行文本文件：

line one
line two
line three
line four
line five

请阅读：

"line one\r\nline two\r\nline three\r\n"

使用以下偶数新文本文件：

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

请阅读：

"line one\r\nline two\r\nline three\r\n"

如何从头到尾读取文件

1 个答案: