Read and parse line in C/C++; put tokens in an array or vector or similar structure

Question

Hello everyone,

I have to submit code to one of the problems in ACM IPC and, as you may know, the time counts a lot. So, I have to read efficiently an input like this: The first line will contain the sequence of integer values associated and the second line will contain the sequence of integer values associated with another sequence. E.g.:

3 2 1 4 5 7 6    
3 1 2 5 6 7 4   
7 8 11 3 5 16 12 18   
8 3 11 7 16 18 12 5   
255  
255

I have to put the 1st line in an array and the second in another and pass both in a function.

How do I read and put these in C/C++? I was thinking in a C way, but my approach would have 2 while's... I have preference reading with scanf, but the parsing can be done as you want.

Please , help this newb!

Answer 1

Read the lines using std:;getline(). Then use a stringstream to parse each line. As this is for a competition, you won't be wanting actual code.

Answer 2

You could also use strtok() and strdup().

See example of using strtok() and strdup(). strtok() would then be used to extract the individual tokens - strdup() to allocate space an copy them.

Answer 3

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

typedef std::vector< int > ints_t;

void dump_ints( const ints_t& input )
{
    std::copy(
        input.begin(),
        input.end(),
        std::ostream_iterator< int >( std::cout, " " ) );
    std::cout << std::endl;
}

void foo( const ints_t& first, const ints_t& second )
{
    dump_ints( first );
    dump_ints( second );
}

bool parse_line( std::istream& is, ints_t* output )
{
    std::string line;
    if ( std::getline( is, line ) )
    {
        std::istringstream raw_ints( line );
        std::copy(
            std::istream_iterator< int >( raw_ints ),
            std::istream_iterator< int >(),
            std::back_inserter( *output ) );
        return true;
    }
    else
    {
        return false;
    }
}

bool parse( std::istream& is, ints_t* first, ints_t* second )
{
    const bool result = parse_line( is, first ) && parse_line( is, second );
    return result;
}

void run( std::istream& is )
{
    while ( is )
    {
        ints_t first;
        ints_t second;
        if ( parse( is, &first, &second ) )
        {
            foo( first, second );
        }
    }
}

int main()
{
    //if you want to read input from file use ifstream and comment istringstream 
//    std::ifstream is( "put_here_a_path_to_input_file" );
    std::istringstream is( 
        "3 2 1 4 5 7 6\n"
        "3 1 2 5 6 7 4\n"
        "7 8 11 3 5 16 12 18\n"
        "8 3 11 7 16 18 12 5\n"
        "255\n"
        "255\n" 
        );
    run( is );
}