C++ - Storing user input string separated by comma

问题:

I have a code written that performs this task to a certain extent. But, I would like to how to alter my code so that I can store as many string inputs the user wants to enters into the vector.

Here is my code:

#include <iostream>
#include <cstring>
#include <vector>

using namespace std;

int main ()
{
string input = "";
cout << "Input: ";
cin >> input;
string a,b;

for(int i = 0; i<input.size(); i++)
{
    if(input.at(i)==','){
        a=input.substr(0,i);
        b=input.substr(i+1);
    }
}

vector<string> objects;
objects.push_back(a);
objects.push_back(b);

for (int k = 0; k < 2; k++) {
    cout << objects[k] << endl;
}

return 0;
}

So far, it can only recognize and store two inputs separated by commas. I am very new to coding so could someone show me a way to make this into a loop and take in as many inputs as the user enters?

Thank you.

回答1:

You need to change your code in order to work for any number of user input. The logic is to push every sub string between the commas into vector.

vector<string> objects;

for(int i = 0,j=0; i<input.size(); i++)
{
    if(input.at(i)==',' || input.at(i)=='\0'){
        objects.push_back(input.substr(j,i-j)); //pushing the sub string
        j=i+1;
    }
}

In order to print the vector first you have to find the size of the vector,then simply iterate over to print it.

//display

int l=objects.size();
for (int k = 0; k < l; k++) {
    cout << objects[k] << endl;
}

Note: If you want your code to work for strings with spaces in between , for example: a ,b ,c ,d then use getline(cin,input); to take input from user.

回答2:

There are much simpler approaches to parse an input string using stringstreams:

string a;
vector<string> objects;

for(stringstream sst(input); getline(sst, a, ','); )  // that's all ! 
    objects.push_back(a);

copy (objects.begin(), objects.end(), ostream_iterator<string>(cout," ; "));  // display all

Online demo

回答3:

You can see running code here or as a github gist.

// Example program
#include <iostream>
#include <string>
#include <vector>
#include <string>

void ParseCSV(
    std::vector< std::string >& output,
    const std::string& csv )
{

    int q = 0;
    int p = csv.find(",");
    while( p != -1 )
    {
        output.push_back( csv.substr(q,p-q) );
        q = p+2;
        p = csv.find(",",q);
    }

    // The terminating comma of the CSV is missing
    // so we need to check if there is
    // one more value to be appended

    p = csv.find_last_of(",");
    if( p != -1 )
    {
        output.push_back( csv.substr( p+2 ) );

    }
    else
    {
        // there was no comma
        // this could be because the list is empty
        // it could also be because there is just one element in the list

        if( csv.length() > 1 )
            output.push_back( csv );
    }
}

int main()
{
    std::string test("this is my list, a, b, c, d, end of line");
    std::vector< std::string > split;
    ParseCSV( split, test );
    for( auto& s : split )
        std::cout << s << std::endl;

}

As suggested by Christophe, using stringstream is much better. No special case handling needed! I use a while loop - it seems clearer what is happening.

void ParseCSV2(
    std::vector< std::string >& output,
    const std::string& csv )
{
    std::stringstream sst(csv);
    std::string a;
    while( getline( sst, a, ',' ) )
        output.push_back(a);
}