Read file and split each line into multiple variable in C++

Question

I have a file of this type:

key1#value1#value2##
key2#value3#value4#value5##
key3#value6##
etc.

I need to read each line, and separate key and values. I've tried different approaches (istringstream & iterator - but I don't know how to explicitly define # as the separator), double getline, I read about boost libraries but I am not sure I would be able to compile it.

I thought another way to do it would be to separate each line into a vector. The first element will always be the key, and vector's size will determine how many values each line had.

What is the best way to split each line?

This question already has an answer http://stackoverflow.com/questions/3946558/c-read-from-text-file-and-separate-into-variable — Tejendra, Mar 09 '15 at 08:44
@Tejendra Incorrect. The mentioned answers does not cover custom delimiter settings, which is in fact the question here. — Géza Török, Mar 09 '15 at 08:49
@Tejendra, the question you linked only provides an answer if the file format uses a value separator (`s`) for which `std::isspace(s)` evaluates to true (tokens separated by spaces, tabs, etc). — utnapistim, Mar 09 '15 at 08:51
Hey, SO people! Why do you downvote _every_ _single_ question regardless of it's worthy or not? I simply don't get why a question about delimiter usage with C++ streams deserve a downvote.. — Géza Török, Mar 09 '15 at 08:51

utnapistim · Accepted Answer · 2015-03-09T10:44:30.957

What is the best way to split each line?

I would simply call while(std::getline(stream, line) to read each line, then for each read line, I would put it into a istringstream (iss), and call while(std::getline(iss, value, '#')) repeatedly (with stream being your initial stream, and line and value being strings). The first value read in the inner loop will be the key; the rest, will be the values.

Some code:

auto read_file(std::istream& in)
{
    using namespace std;
    map<string, vector<string>> values;
    string line;
    while(getline(in, line))
    {
        istringstream linein{ line };
        string key, value;
        if(!getline(linein, key, '#'))
            throw runtime_error{ "bad file format" };
        while(getline(linein, value, '#') && !value.empty())
            values[key].emplace_back(move(value));
    }
    return values;
}

std::ifstream in{ "file-of-this-type.txt" };
auto values = read_file(in);

And probably store everything in a `std::map>`. – Christian Hackl Mar 09 '15 at 08:54 — Christian Hackl, Mar 09 '15 at 08:54

score 0 · Answer 2 · edited May 23 '17 at 12:12

0

You can get each line as a String. After that use this information Split a string in C++? It's very useful

edited May 23 '17 at 12:12

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answered Mar 09 '15 at 08:43

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Read file and split each line into multiple variable in C++

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