C ++：为什么我的（置换索引）代码不能正确打印出来？

Question

I'm walking myself though Accelerated C++'s problems and this is the first one i'm having any sort of trouble with.

The problem is to code a program that is able to generate a permuted index from a set of lines.

The code below has two functions: permutedIndex5_1 which is the "main()" function of sorts, and permuteLine5_1 which takes a given line (and a reference to an vector of already permuted lines) and permutes the given line rotationally, adding each rotation to the vector.

The problem i'm having is that the permuted lines are printing out incorrectly on stdout. I've included several 3 debug statements in permuteLine5_1 to test the first and last strings to be printed, and the results of those print statements show what should be printed out, however what is being printed out is completely different.

My gut feeling is that it may have to do with me erasing the iterator in that function, but i'm not sure how to rectify it. In any case, any help would be appreciated.

EDIT: The contents of the text file read are :

The quick brown fox
The slow brown fox
The quick blue dog

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


using std::fstream;
using std::ios;
using std::istringstream;
using std::vector;
using std::string;
using std::cin;
using std::cout;
using std::endl;

void permuteLine5_1(vector< vector<string> >& lines, vector<string> curLine)
{

    for(int i = 0; i < curLine.size(); i++)
    {
        vector<string>::iterator curBeginStrItr = curLine.begin();
        string curBeginStr = *curBeginStrItr;

        curLine.erase(curBeginStrItr);
        curLine.push_back(curBeginStr);

        cout << "The first string in the current line is : "  + *(curLine.begin()) << endl;
        cout << "The first string in the current line is VIA INDEXING IS : "  + curLine[0] << endl;
        cout << "The last string in the current line is : "  + *(curLine.rbegin()) << endl;

        for(int j = 0; j < curLine.size(); j++)
        {
            cout << curLine[j];
        }
        cout << endl;

        lines.push_back(curLine);
    }


}

void permutedIndex5_1()
{
    vector< vector<string> > lines;

    fstream fileLines;
    fileLines.open("C:\\Users\\Kevin\\Desktop\\lines.txt", ios::in);

    string curLine, curWord;
    vector<string> curLineVec;

    while(getline(fileLines, curLine))
    {
        cout << curLine << endl;

        curLineVec.push_back("|");

        istringstream strS(curLine);

        while(getline(strS, curWord, ' '))
        {
            curLineVec.push_back(curWord);
            cout << curWord << endl;  
        }

        lines.push_back(curLineVec);
        curLineVec.clear();
    }

    vector< vector<string> > permuted;

    for(int i = 0; i < lines.size(); i++)
    {
        permuteLine5_1(permuted, lines[i]);
    }

    sort(permuted.begin(), permuted.end());

    /*Code below prints out permutations. Commented out because
      permuting function does not work properly

    for(int i = 0; i < permuted.size(); i++)
    {
        vector<string> curVec = permuted[i];
        for(int j = 0; j < curVec.size(); j++)
        {
            cout << curVec[j] << ' ';
        }

        cout << endl;
    }*/


}

Answer 1

I think your iterator erasing is fine, because you make a real copy of the string first, and your invalidated iterator is not subsequently used.

I'd simplify the permutation a bit to...

for(int i = 0; i < curLine.size(); i++)
{
    string curBeginStr = curLine[0];

    curLine.erase(curLine.begin());
    curLine.push_back(curBeginStr);

But, I think the real problem is in the sort, and I'm a bit surprised it compiles:

 
 
 
  
  sort(permuted.begin(), permuted.end());
 
  

You're trying to sort a vector of vectors of string - which means that the sort algorithm needs to somehow compare two vectors of strings to determine order. I think it can't do that, and that you'll need to provide a custom sorting predicate to perform the exact comparison you want.

Thanks to Chris for the correction.