Readin a line from console c++

Question

I am new to c++ and I am a bit lost here!

I am trying to read the following line

* - 6 + x -6 - - 9 6 * 0 c

and I am iterating through the characters using

    for (std::string line; std::getline(std::cin, line);) {
        for(auto c : line){
          if(c != ' ')
        }
    }

now I am expecting to get "-6" at the sixth iteration but a I am getting "-" and then at the next iteration I am getting 6, I need to get "-6"! any help!

question from:https://stackoverflow.com/questions/65836080/readin-a-line-from-console-c

Answer 1

In the outer for loop, you are infinitely looping until getline() evaluates to false. In the inner for loop, you are looping through each character in line.

I don't know of any elegant syntax to parse a string into tokens like it seems you are trying to do. One way is to utilise std::stringstream and put things into an array or vector. Below is a sample main I wrote demonstrating how versatile this is:

#include <iostream>
#include <sstream>
#include <vector>

int main() {
    
    std::string line;
    while ( true ) {
        std::cout << "Enter parse string: ";
        std::getline( std::cin, line );
        
        if ( line == "Stop" ) break;        // Enter stop to quit program
        
        std::stringstream ss( line );       // constructor sets 'line' as contents of the stream
        std::vector <std::string> tokens;   // where our tokenised input is stored
        std::string temp;                   // where current token is temporarily loaded before it's put into the vector
        
        while( getline( ss, temp, ' ' ) )   // extract characters from ss until a space is found and stores them in temp
            tokens.push_back( temp );       // put the token formed by getline in our vector, from back so order is kept
        
        /*
         
          Now you can use the vector as you would like. Below the contents are printed.
        
         */
        
        for ( auto& x : tokens )            // for each token in 'tokens' vector,
            std::cout << x << ' ';          // print out token with a space at the end
    
        std::cout << "

";
        
        for ( int i = 0; i < tokens.size(); i++ )           // for each token in 'tokens' vector,
            std::cout << i << ": " << tokens[i] << '
';    // print out index number and token
        
        std::cout << std::endl;             // newline & flush
    }
    
    return 0;
}

If you want to abstract the details away, you could always wrap the std::stringstream stuff into a function that takes in a string and returns a std::vector<std::string>. Below I demonstrate what that would look like:

#include <iostream>
#include <sstream>
#include <vector>

std::vector <std::string> toParsedVector( std::string input ) {
    
    std::stringstream ss( input );      // constructor sets 'line' as contents of the stream
    std::vector <std::string> tokens;   // where our tokenised input is stored
    std::string temp;                   // where current token is temporarily loaded before it's put into the vector
    
    while( getline( ss, temp, ' ' ) )   // extract characters from ss until a space is found and stores them in temp
        tokens.push_back( temp );       // put the token formed by getline in our vector, from back so order is kept

    return tokens;
}

int main() {
    
    std::string line;
    while ( true ) {
        std::cout << "Enter parse string: ";
        std::getline( std::cin, line );
        
        if ( line == "Stop" ) break;        // Enter stop to quit program
        
        std::vector <std::string> tokens = toParsedVector( line ); // create vector
        
        // Now you can use the vector (tokens) as you would like. Below the contents are printed.
        
        for ( auto& x : tokens )            // for each token in 'tokens' vector,
            std::cout << x << ' ';          // print out token with a space at the end
    
        std::cout << "

";
        
        for ( int i = 0; i < tokens.size(); i++ )           // for each token in 'tokens' vector,
            std::cout << i << ": " << tokens[i] << '
';    // print out index number and token
        
        std::cout << std::endl;             // newline & flush
    }
    
    return 0;
}

I hope this helps; might not be the most elegant solution, but it is very versatile.