在 C++ 中显示字符串向量

Question

I'm sorry if this is a repeat question but I already tried to search for an answer and came up empty handed. So basically I just want to add strings (single words) to the back of a vector and then display the stored strings as a single string. I am quite the rookie.

#include <iostream>
#include <vector>
#include <string>
#include <cctype>
using namespace std;


int main(int a, char* b [])
{
    vector<string> userString;      
    string word;        
    string sentence = "";           
    for (decltype(userString.size()) i = 0; i <= userString.size() - 1; i++)
    {
        cin >> word;
        userString.push_back(word);
        sentence += userString[i] + " ";
    }
    cout << sentence;
    system("PAUSE");
    return 0;
}

Why doesn't this work?

EDIT

int main(int a, char* b [])
{
    cout << "Enter a sequence of words. Enter '.' \n";
    vector<string> userString;      
    string word;                    
    string sentence = "";           /
    int wordCount = 0;
    while (getline(cin, word))
    {
        if (word == ".")
        {
            break;
        }
        userString.push_back(word);
    }
    for (decltype(userString.size()) i = 0; i <= userString.size() - 1; i++)
    {
        sentence += userString[i] + " ";
        wordCount += 1;
        if (wordCount == 8)
        {
            sentence = sentence + "\n";
                    wordCount = 0;
        }
    }
    cout << sentence << endl; 
    system("PAUSE");
    return 0;
}

So my new program works. It just puts values at the back of a vector and prints them out 8 words to a line. I know there's easier ways but I'm just learning vectors and I'm going in baby steps. Thanks for the help guys.

Answer 1

Because userString is empty. You only declare it

vector<string> userString;     

but never add anything, so the for loop won't even run.

Answer 2

Your vector<string> userString has size 0 , so the loop is never entered. You could start with a vector of a given size:

vector<string> userString(10);      
string word;        
string sentence;           
for (decltype(userString.size()) i = 0; i < userString.size(); ++i)
{
    cin >> word;
    userString[i] = word;
    sentence += userString[i] + " ";
}

although it is not clear why you need the vector at all:

string word;        
string sentence;           
for (int i = 0; i < 10; ++i)
{
    cin >> word;
    sentence += word + " ";
}

If you don't want to have a fixed limit on the number of input words, you can use std::getline in a while loop, checking against a certain input, eg "q" :

while (std::getline(std::cin, word) && word != "q")
{
    sentence += word + " ";
}

This will add words to sentence until you type "q".

Answer 3

You have to insert the elements using the method present in vectors STL, check the below program to add the elements to it, and you can use in the same way in your program.

#include <iostream>
#include <vector>
#include <string.h>

int main ()
{
  std::vector<std::string> myvector ;
  std::vector<std::string>::iterator it;

   it = myvector.begin();
  std::string myarray [] = { "Hi","hello","wassup" };
  myvector.insert (myvector.begin(), myarray, myarray+3);

  std::cout << "myvector contains:";
  for (it=myvector.begin(); it<myvector.end(); it++)
    std::cout << ' ' << *it;
    std::cout << '\n';

  return 0;
}

Answer 4

You ask two questions; your title says "Displaying a vector of strings", but you're not actually doing that, you actually build a single string composed of all the strings and output that.

Your question body asks "Why doesn't this work".

It doesn't work because your for loop is constrained by "userString.size()" which is 0, and you test your loop variable for being "userString.size() - 1". The condition of a for() loop is tested before permitting execution of the first iteration.

int n = 1;
for (int i = 1; i < n; ++i) {
    std::cout << i << endl;
}

will print exactly nothing.

So your loop executes exactly no iterations, leaving userString and sentence empty.

Lastly, your code has absolutely zero reason to use a vector. The fact that you used "decltype(userString.size())" instead of "size_t" or "auto", while claiming to be a rookie, suggests you're either reading a book from back to front or you are setting yourself up to fail a class.

So to answer your question at the end of your post: It doesn't work because you didn't step through it with a debugger and inspect the values as it went. While I say it tongue-in-cheek, I'm going to leave it out there.

Answer 5

vector.size() returns the size of a vector. You didn't put any string in the vector before the loop , so the size of the vector is 0. It will never enter the loop. First put some data in the vector and then try to add them. You can take input from the user for the number of string user wants to enter.

#include <iostream>
#include <vector>
#include <string>
#include <cctype>
using namespace std;


int main(int a, char* b [])
{
    vector<string> userString;
    string word;
    string sentence = "";
    int SIZE;
    cin>>SIZE;    //what will be the size of the vector
    for (int i = 0; i < SIZE; i++)
    {
        cin >> word;
        userString.push_back(word);
        sentence += userString[i] + " ";
    }
    cout << sentence;
    system("PAUSE");
    return 0;
}

another thing, actually you don't have to use a vector to do this.Two strings can do the job for you.

#include <iostream>
#include <vector>
#include <string>
#include <cctype>
using namespace std;


int main(int a, char* b [])
{
   // vector<string> userString;
    string word;
    string sentence = "";
    int SIZE;
    cin>>SIZE;    //what will be the size of the vector
    for (int i = 0; i < SIZE; i++)
    {
        cin >> word;
        sentence += word+ " ";
    }
    cout << sentence;
    system("PAUSE");
    return 0;
}

and if you want to enter string until the user wish , code will be like this:

#include <iostream>
#include <vector>
#include <string>
#include <cctype>
using namespace std;


int main(int a, char* b [])
{
   // vector<string> userString;
    string word;
    string sentence = "";
    //int SIZE;
    //cin>>SIZE;    //what will be the size of the vector
    while(cin>>word)
    {
        //cin >> word;
        sentence += word+ " ";
    }
    cout << sentence;
  //  system("PAUSE");
    return 0;
}

Answer 6

This code works without any modifications though.

Source: https://gist.github.com/lucianmachado/9a26d5745497ffe5d054

#include <glob.h>
#include <vector>
#include <string>
inline std::vector<std::string> glob(const std::string& pat){
    using namespace std;
    glob_t glob_result;
    glob(pat.c_str(),GLOB_TILDE,NULL,&glob_result);
    vector<string> ret;
    for(unsigned int i=0;i<glob_result.gl_pathc;++i){
        ret.push_back(string(glob_result.gl_pathv[i]));
    }
    globfree(&glob_result);
    return ret;
}

Use it like:

glob("pattern");

"pattern" could also be a string.c_str(). It also returns the strings so you can catch it too in a string variable for instance.