快速Q-无法写入文件功能输出

Question

Code :

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

using namespace std;

void printVector (const vector<string>& theVect, vector<bool>& bArray, int nItems){
    for (int i = 0; i < nItems; ++i)
       if (bArray[i] == true)
         cout << theVect[i] << " ";
         outFile << theVect[i];
    cout << "\n";
    outFile << "\n";
}

void nCombination(const vector<string> &Vect,int n, int r){

    vector<bool> myBits(n, false);  // everything is false now
    int count = 1; 
    for (size_t i = n-1; i >= 0 && count <= r; --i, ++count){
        myBits[i] = true;
    }
    do  // start combination generator
    {
       printVector(Vect, myBits, n );
    } while (next_permutation(myBits.begin(), myBits.end()));;  // change the bit pattern
}

void nPermutation(vector<string> o, int r){
    do {
        for(int count = 0; count < r; count++){
        cout << o[count] << " " ;
        outFile << o[count] << " ";
    }
        cout<< endl;
        outFile << endl;
    } 
    while (next_permutation(o.begin(), o.end()));
}

int main(int argc, char** argv) {

int numofOps;
char Op;
int n;
int r;
string line;

    ifstream myFile("infile.dat");
    myFile >> numofOps;
    myFile.ignore(1,'\n');

    ofstream outFile;
    outFile.open ("example.txt");

    for(int q = 0; q < numofOps; ++q){
    myFile.get(Op);
    myFile >> n;
    myFile>> r;

    vector<string> original(n);
    for(int i = 0;i <= n - 1; i++){
        myFile.ignore(1,'\n');
        myFile >> original[i];}

    myFile.ignore(1,'\n');

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

    cout<< '\n'<< endl;


    if(Op == 'P'){
        nPermutation(original, r);
    }
    else{
        if(Op == 'C')
            nCombination(original,n,r);
        else
            cout << "Incorrect Input" << endl;
    }
    original.clear();
    }
    outFile.close();
    return 0;
}

My code works but when I add in the outFile to write everything to a file called example, it doesn't work. How can I print out the result of the functions??

Examples would be so nice!!

Answer 1

One immediate problem springing to mind:

if (bArray[i] == true)
     cout << theVect[i] << " ";
     outFile << theVect[i];

Python is the only language I'm aware of that uses indentation to control blocking of statements. In C-based languages, you should use braces:

if (bArray[i] == true) {
     cout << theVect[i] << " ";
     outFile << theVect[i];
}

---

On top of that, the code you've given shouldn't even compile. You create outFile as a local parameter inside main() then attempt to use it in the other functions, where it's not accessible.

You should either make it "global" by moving it out of main() so that every function can see it (unwise, but probably the quickest solution here) or pass it as a parameter to each function that needs to use it.

For the former, you could use:

using namespace std;
ofstream outFile;     // taken from main().

For the latter, it's a matter of adding it for each call to printVector() , nCombination() and nPermutation() , and modifying those functions so that they accept it, for example:

void nPermutation (
    vector<string> o,
    int            r,
    ofstream       os
) {
    os << "blah blah blah\n";
}
:
nPermutation (original, r, outFile);