我可以改进从文件中读取字符串吗？ [复制]

Question

我正在尝试将逗号分隔文件中的数据读入字符串。此外，我希望从字符串中删除多余的空格。

我已经设法实施了一个可行的解决方案，但我很感兴趣如果这可以更有效地完成。我的主要目标是删除具有默认字符串大小（std::string lName( 100, 0 );）的临时字符串初始化，因为文件中的数据是可变长度的。

另外，如果您有一些建设性的建议，我将不胜感激。

我正在使用 MS Visual Studio 2008。

这是 SSCCE 示例：

#include <iostream>
#include <algorithm>
#include <string>
#include <fstream>

// helper function for removing extra spaces
void removeSpace( std::string &str )
{
    str.erase( std::remove( str.begin(), str.end(), ' ' ), str.end() );
}

int main()
{
    //========== let us construct a test file =====================//
    //===== format is Last Name, First Name, Gender, Color, Birth Date =======//
    std::ofstream os;
    os.open( "test.txt" );

    // first row
    os << " Smith  ," << " John  ," << "   Male , " 
        << " Green  , " << " 6  / 7 / 1960  \n";

    // second row
    os << " Mortensen ," << " Mike  ," << " Male  , " 
        << " Red  , " << "5/5/  1975 \n";

    // third row
    os << " Johnson ," << " Ann  ," << " Female , " 
        << " Blue , " << " 4/ 4 /1985 \n";

    os.close();

    // now let us read data from it
    std::ifstream g;
    g.open( "test.txt" );

    if( g.is_open() )
    {
        while( !g.eof() )
        {
            // temporary strings
            std::string lName( 100, 0 );
            std::string fName( 100, 0 );
            std::string gen( 100, 0 );
            std::string clr( 100, 0 );
            std::string date( 100, 0 );

            // get data from file
            g.getline( &lName[0], 100, ',' );
            g.getline( &fName[0], 100, ',' );
            g.getline( &gen[0], 100, ',' );
            g.getline( &clr[0], 100, ',' );
            g.getline( &date[0], 100 );

            // remove extra spaces from strings
            removeSpace( lName );
            removeSpace( fName );
            removeSpace( gen );
            removeSpace( clr );
            removeSpace( date );

            // display the result
            std::cout << lName.c_str() 
                << ' ' << fName.c_str() 
                << ' ' << gen.c_str()
                << ' ' << clr.c_str()
                << ' ' << date.c_str()
                << std::endl;

            //cleanup
            lName.clear();
            fName.clear();
            gen.clear();
            clr.clear();
            date.clear();
        }
        g.close();
    }

    // since our SSCCE example is done, let us delete the test file
    if( 0 != std::remove( "test.txt" ) )
        std::cout << "Couldn't delete test file!\n\n";
    else
        std::cout << "Successfully deleted test file!\n\n";

    return 0;
}

编辑：

根据成员 WhozCraig 的建议，我能够做出改进。为简洁起见，我将只发布while 循环：

while( !g.eof() )
{
    // temporary strings
    std::string line;

    if( ! std::getline( g, line ) )
        break;

    std::istringstream iss(line);

    while( iss )
    {
        std::string str;

        if ( ! std::getline( iss, str, ',' ) ) 
            break;

        // remove excess spaces
        removeSpace( str );
        // output the result
        std:: cout << str.c_str() << ' ';
    }

    std::cout << std::endl;
}

Answer 1

对于微不足道的逗号分隔（与真实的 CSV 格式相反，这远远超出了您最初问题的范围），明智地使用 std::getline 和 std::istringstream 可能会让您摆脱困境，尤其是当它来到逐行资格。我冒昧fix the while-conditon as well，

下面的完全修改示例。祝你好运。 （并且 +1 是因为您使用 remove-erase-idiom 来剥离您的空间。）

#include <iostream>
#include <fstream>
#include <sstream>
#include <algorithm>
#include <string>

// helper function for removing extra spaces
void removeSpace( std::string &str )
{
    str.erase( std::remove( str.begin(), str.end(), ' ' ), str.end() );
}

int main()
{
    //===== format is Last Name, First Name, Gender, Color, Birth Date =======//
    std::ofstream os;
    os.open( "test.txt" );

    // first row
    os << " Smith  ," << " John  ," << "   Male , "
    << " Green  , " << " 6  / 7 / 1960  \n";

    // second row
    os << " Mortensen ," << " Mike  ," << " Male  , "
    << " Red  , " << "5/5/  1975 \n";

    // third row
    os << " Johnson ," << " Ann  ," << " Female , "
    << " Blue , " << " 4/ 4 /1985 \n";

    os.close();

    // now let us read data from it
    std::ifstream g;
    g.open( "test.txt" );

    if( g.is_open() )
    {
        std::string line;
        while( std::getline(g, line) )
        {
            std::istringstream iss(line);
            std::string lName, fName, gen, clr, date;
            if (std::getline(iss, lName, ',') &&
                std::getline(iss, fName, ',') &&
                std::getline(iss, gen, ',') &&
                std::getline(iss, clr, ',') &&
                std::getline(iss, date))
            {
                // remove extra spaces from strings
                removeSpace( lName );
                removeSpace( fName );
                removeSpace( gen );
                removeSpace( clr );
                removeSpace( date );

                // display the result
                std::cout << lName
                          << ' ' << fName
                          << ' ' << gen
                          << ' ' << clr
                          << ' ' << date << '\n';
            }
        }
        g.close();
    }

    // since our SSCCE example is done, let us delete the test file
    if( 0 != std::remove( "test.txt" ) )
        std::cout << "Couldn't delete test file!\n\n";
    else
        std::cout << "Successfully deleted test file!\n\n";

    return 0;
}

输出

Smith John Male Green 6/7/1960
Mortensen Mike Male Red 5/5/1975
Johnson Ann Female Blue 4/4/1985