cout 字符串和向量在同一行

Question

每当我将string 和vector 放在同一行时，字符串就会变为空。 在我的代码中，

string line, s1, s2; 
vector<pair<string,int> > binaryvector;
ifstream filename(uncompr_filename.c_str());

如果我这样做

while(getline(filename, line))
{
    s1 = line.c_str();
    s2 = binaryvector[0].first.c_str();
    cout << s1 << endl;
    cout << s2 << endl;
}

它同时打印 s1 和 s2 的值。 但如果我这样做，

while(getline(filename, line))
{
    s1 = line.c_str();
    s2 = binaryvector[0].first.c_str();
    cout << s1 << s2 << endl;
}

它只打印 s2 字符串。我哪里错了？ 这只是为了说明问题。我实际上想要做的是使用 if(s1 == s2) 比较 s1 和 s2。但如果我这样做，它会返回 false，因为 s1 似乎没有任何内容并且不等于 s2 字符串。

完整的代码。

#include <iostream>
#include <fstream>
#include <algorithm>
#include <string>
#include <map>
#include <vector>
#define DICTIONARYSIZE 4

using namespace std;
typedef map<string,int> Instruction_Binaries;
struct val_greaterthan : binary_function < pair<string,int>, pair<string,int>, bool >
{
        bool operator() (const pair<string,int>& x, const pair<string,int>& y) const
        {return x.second > y.second;}
}val_gt;

int main(int argc, char *argv[])
{
    int c, i;
    Instruction_Binaries binary_count;
    string uncompr_filename, compr_filename, outfilename;

        if(argc <= 3)
        {
                cout << "Format is \"./SIM -c original.txt cout.txt\" or \"./SIM -d compressed.txt dout.txt\"" << endl;
                return 1;
        }
    while ((c = getopt (argc, argv, "c:d:")) != -1)
        switch (c)
        {
                case 'c':
                        (uncompr_filename=optarg);
                        break;
                case 'd':
                        (compr_filename=optarg);
                        break;
                default:
                        cout << "Format is \"./SIM -c original.txt cout.txt\" or \"./SIM -d compressed.txt dout.txt\"" << endl;
                        abort ();
                        break;
        }

    ifstream ifile(uncompr_filename.c_str());
    string binary, Directory_Index;

    while (ifile >> binary){
        int index;
        ++binary_count[binary];
    }

    vector<pair<string,int> > binaryvector;
    copy(binary_count.begin(), binary_count.end(), back_inserter(binaryvector));
    sort(binaryvector.begin(), binaryvector.end(), val_gt);

    while(ifile >> binary){
        int flag = 0;
        for(i=0; i<4; ++i){
                if(i==0) Directory_Index = "00";
                else if(i==1) Directory_Index = "01";
                else if(i==2) Directory_Index = "10";
                else if(i==3) Directory_Index = "11";
                if(binary == binaryvector[i].first){
                        cout << "001" << Directory_Index << endl;
                        flag=1;
                        break;
                }
        }
    if(flag == 0)
                cout << binary << endl;
    }
    return 0;
}

Answer 1

问题出在代码中的其他地方，因为它有效：

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

using namespace std;

int main()
{
    string line, s1, s2; 
    vector<pair<string,int> > binaryvector;
    binaryvector.push_back({"heya", 5});
    ifstream filename("input.txt");

    while(getline(filename, line))
    {
        s1 = line.c_str();
        s2 = binaryvector[0].first.c_str();
        cout << s1 << s2 << endl;
    }
    return 0;
}

我在http://www.compileonline.com/compile_cpp11_online.php 上运行了这个，输入文件如下所示：

This is the file you can use to provide input to your program and later on open it inside your program to process the input.
second line
third line

After a blank line!  Booya!
and a line without "ending" it

输出如下所示：

This is the file you can use to provide input to your program and later on open it inside your program to process the input.
heya
second line
heya
third line
heya
heya
After a blank line! Booya!
heya
and a line without "ending" itheya

这意味着cout 没有问题，但你在某处做错了其他可怕的事情，因为我刚刚制作的“最小”程序 100% 可以解决你的“受限”问题。