从文本文件中读取行并将字符串放入向量中？

Question

我正在尝试读取每行包含一个单词的文本文件的每一行，并将这些单词放入一个向量中。我该怎么做呢？

这是我的新代码：我觉得还是有问题。

#include <iostream>
#include <fstream>
#include <string>
#include <vector>
using namespace std;

int main()
{
    std::string line;
    vector<string> DataArray;
    vector<string> QueryArray;
    ifstream myfile("OHenry.txt");
    ifstream qfile("queries.txt");

    if(!myfile) //Always test the file open.
    {
        cout<<"Error opening output file"<<endl;
        system("pause");
        return -1;
    }
    while (std::getline(qfile, line))
    {
        QueryArray.push_back(line);
    }
    if(!qfile) //Always test the file open.
    {
        cout<<"Error opening output file"<<endl;
        system("pause");
        return -1;
    }

    while (std::getline(qfile, line))
    {
        QueryArray.push_back(line);
    }

    cout<<QueryArray[0]<<endl;
    cout<<DataArray[0]<<endl;

}

Answer 1

@FailedDev 确实列出了最简单的形式。作为替代方案，这是我经常编写该循环的方式：

std::vector<std::string> myLines;
std::copy(std::istream_iterator<std::string>(myfile),
          std::istream_iterator<std::string>(),
          std::back_inserter(myLines));

整个程序可能如下所示：

// Avoid "using namespace std;" at all costs. Prefer typing out "std::"
// in front of each identifier, but "using std::NAME" isn't (very) dangerous.
#include <iostream>
using std::cout;
using std::cin;
#include <fstream>
using std::ifstream;
#include <string>
using std::string;
#include <vector>
using std::vector;
#include <iterator>
using std::istream_iterator;
#include <algorithm>
using std::copy;

int main()
{

    // Store the words from the two files into these two vectors
    vector<string> DataArray;
    vector<string> QueryArray;

    // Create two input streams, opening the named files in the process.
    // You only need to check for failure if you want to distinguish
    // between "no file" and "empty file". In this example, the two
    // situations are equivalent.
    ifstream myfile("OHenry.txt"); 
    ifstream qfile("queries.txt");

    // std::copy(InputIt first, InputIt last, OutputIt out) copies all
    //   of the data in the range [first, last) to the output iterator "out"
    // istream_iterator() is an input iterator that reads items from the
    //   named file stream
    // back_inserter() returns an interator that performs "push_back"
    //   on the named vector.
    copy(istream_iterator<string>(myfile),
         istream_iterator<string>(),
         back_inserter(DataArray));
    copy(istream_iterator<string>(qfile),
         istream_iterator<string>(),
         back_inserter(QueryArray));

    try {
        // use ".at()" and catch the resulting exception if there is any
        // chance that the index is bogus. Since we are reading external files,
        // there is every chance that the index is bogus.
        cout<<QueryArray.at(20)<<"\n";
        cout<<DataArray.at(12)<<"\n";
    } catch(...) {
        // deal with error here. Maybe:
        //   the input file doesn't exist
        //   the ifstream creation failed for some other reason
        //   the string reads didn't work
        cout << "Data Unavailable\n";
    }
}

Answer 2

最简单的形式：

std::string line;
std::vector<std::string> myLines;
while (std::getline(myfile, line))
{
   myLines.push_back(line);
}

不需要疯狂的 c 东西 :)

编辑：

#include <iostream>
#include <fstream>
#include <string>
#include <vector>

int main()

{
    std::string line;
    std::vector<std::string> DataArray;
    std::vector<std::string> QueryArray;
    std::ifstream myfile("OHenry.txt");
    std::ifstream qfile("queries.txt");

    if(!myfile) //Always test the file open.
    {
        std::cout<<"Error opening output file"<< std::endl;
        system("pause");
        return -1;
    }
    while (std::getline(myfile, line))
    {
        DataArray.push_back(line);
    }

    if(!qfile) //Always test the file open.
    {
        std::cout<<"Error opening output file"<<std::endl;
        system("pause");
        return -1;
    }

    while (std::getline(qfile, line))
    {
        QueryArray.push_back(line);
    }

    std::cout<<QueryArray[20]<<std::endl;
    std::cout<<DataArray[12]<<std::endl;
    return 0;
}

使用的关键字是非法的 C++！永远不要使用它。好吗？ 很好。现在比较我写的和你写的，试着找出不同之处。如果您仍有问题，请回来。

Answer 3

最简单的版本：

std::vector<std::string> lines;
for (std::string line; std::getline( ifs, line ); /**/ )
   lines.push_back( line );

我省略了包含和其他垃圾。我的版本与 FailedDev 的版本几乎相同，但通过使用“for”循环，我将“line”的声明放入循环中。这不仅仅是减少行数的技巧。这样做会缩小行的范围——它在 for 循环之后消失。所有变量都应该具有尽可能小的范围，因此这更好。 for 循环很棒。

Answer 4

适用于 C++11 及更高版本的简短版本。向量是直接从文件内容构造的：

ifstream qfile("queries.txt");
vector<string> lines {
    istream_iterator<string>(qfile),
    istream_iterator<string>()
};

请注意，此代码仅在输入文件采用 OP 描述的格式时才有效，即“每一行包含一个单词”。或者，如果您通过 qfile.imbue() 设置特殊语言环境，正如 mheyman 所指出的那样。