CODEWITHSUNDEEP
c++file-iointegerstring-parsing
droidmachine
droidmachine

Reputation: 577

How to read integers from txt file by skipping =?

1 = 0 0 97 218
2 = 588 0 97 218
3 = 196 438 97 218
4 = 0 657 97 218
5 = 294 438 97 218

I have txt file like above.How can i read only integers from this file without = ?

Upvotes: 0

Views: 296

Answers (2)

Jerry Coffin
Jerry Coffin

Reputation: 490048

Another possibility would be a facet that classifies = as white space:

class my_ctype : public std::ctype<char>
{
    mask my_table[table_size];
public:
    my_ctype(size_t refs = 0)  
        : std::ctype<char>(&my_table[0], false, refs)
    {
        std::copy_n(classic_table(), table_size, my_table);
        my_table['='] = (mask)space;
    }
};

Then imbue your stream with a locale including this facet, then read the numbers as if the = wasn't there at all:

int main() {
    std::istringstream input(
            "1 = 0 0 97 218\n"
            "2 = 588 0 97 218\n"
            "3 = 196 438 97 218\n"
            "4 = 0 657 97 218\n"
            "5 = 294 438 97 218\n"
        );

    std::locale x(std::locale::classic(), new my_ctype);
    input.imbue(x);

    std::vector<int> numbers((std::istream_iterator<int>(input)),
        std::istream_iterator<int>());

    std::cout << "the numbers add up to: " 
              << std::accumulate(numbers.begin(), numbers.end(), 0) 
              << "\n";
    return 0;
}

Granted, it's probably not very sensible to add up all the numbers, since the first one on each line seems to be a line number -- that's just a quick demo to show that we're really reading the numbers without the extra "stuff" causing any problems.

Upvotes: 1

Kerrek SB
Kerrek SB

Reputation: 476950

Here's the basic framework: read line-by-line and parse.

for (std::string line; std::getline(std::cin, line); )
{
     std::istringstream iss(line);
     int n;
     char c;

     if (!(iss >> n >> c) || c != '=')
     {
         // parsing error, skipping line
         continue;
     }

     for (int i; iss >> i; )
     {
         std::cout << n << " = " << i << std::endl; // or whatever;
     }
}

To read a file via std::cin, pipe it into your program, like ./myprog < thefile.txt.

Upvotes: 0

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