c – 使用迭代器正确读取和写入std :: vector到文件中

发布时间：2020-12-16 10:36:34 所属栏目：百科来源：网络整理

导读：我试图理解 here提供的答案,但我似乎无法使其发挥作用. 这是我尝试过的： #include algorithm#include iostream#include iterator#include vector#include fstreamint main(){ std::string path("numbersfile"); std::vectorint myVector{1,16,32,64}; std::

我试图理解 here提供的答案,但我似乎无法使其发挥作用.

这是我尝试过的：

#include <algorithm>
#include <iostream>
#include <iterator>
#include <vector>
#include <fstream>

int main()
{
    std::string path("numbersfile");

    std::vector<int> myVector{1,16,32,64};
    std::vector<int> newVector{};

    std::ofstream FILE(path,std::ios::out | std::ofstream::binary);
    std::copy(myVector.begin(),myVector.end(),std::ostreambuf_iterator<char>(FILE));

    std::ifstream INFILE(path,std::ios::in | std::ifstream::binary);
    std::istreambuf_iterator<char> iter(INFILE);
    //std::copy(iter.begin(),iter.end(),std::back_inserter(newVector)); //this doesn't compile
    std::copy(iter,std::istreambuf_iterator<char>{},std::back_inserter(newVector)); // this leaves newVector empty
}

最后一次复制后,newVector仍为空.如何更新最后一个语句以填充newVector？

解决方法

在调用第二个副本时,文件尚未准备好读取. (感谢Piotr Skotnicki在评论中的回答)

拨打flush可以使程序正常工作：

#include <algorithm>
#include <iostream>
#include <iterator>
#include <vector>
#include <fstream>

int main()
{
    std::string path("numbersfile");

    std::vector<int> myVector{1,std::ostreambuf_iterator<char>(FILE));
    FILE.flush(); // required here

    std::ifstream INFILE(path,std::back_inserter(newVector)); // this leaves newVector empty
    return 0;
}

创建ifstream时,ofstream仍在范围内.如果已经调用了ofstream的析构函数,那么该文件也已经为ifstream做好了准备.在以下程序中,ifstream会自动销毁：

#include <algorithm>
#include <fstream>
#include <iterator>
#include <vector>

std::string filename("numbersfile");

std::vector<double> myVector{1.342,16.33,32.1,12364};

void write_vector_to_file(const std::vector<double>& myVector,std::string filename);
std::vector<double> read_vector_from_file(std::string filename);

int main()
{
    write_vector_to_file(myVector,filename);
    auto newVector{read_vector_from_file(filename)};
    return 0;
}

void write_vector_to_file(const std::vector<double>& myVector,std::string filename)
{
    std::ofstream ofs(filename,std::ios::out | std::ofstream::binary);
    std::ostream_iterator<double> osi{ofs," "};
    std::copy(myVector.begin(),osi);
}

std::vector<double> read_vector_from_file(std::string filename)
{
    std::vector<double> newVector{};
    std::ifstream ifs(filename,std::ios::in | std::ifstream::binary);
    std::istream_iterator<double> iter{ifs};
    std::istream_iterator<double> end{};
    std::copy(iter,end,std::back_inserter(newVector));
    return newVector;
}

（编辑：李大同）

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