reader.cpp

#include <fstream>
#include <vector>
#include <stdexcept>
#include <iostream>
#include <boost/lexical_cast.hpp>

using namespace std;
using boost::lexical_cast;

vector<double> readMatrix(istream& stream, string const& name)
{
    string actual_name;
    int row_count, col_count;
    stream >> actual_name >> row_count >> col_count;
    if (!stream)
        throw std::runtime_error("error reading vector " + name);
    else if (actual_name != name)
        throw std::runtime_error("expected to get vector " + name + " but got " + actual_name);


    size_t count = row_count * col_count;
    vector<double> values;
    values.reserve(row_count * col_count);
    for (int i = 0; i < count; ++i)
    {
        double v;
        stream >> v; 
        if (!stream)
            throw std::runtime_error("not enough values for " + name + " expected " + lexical_cast<string>(count) + " but got only " + lexical_cast<string>(i + 1));

        values.push_back(v);
    }
    return values;
}

int main(int argc, char** argv)
{
    ifstream stream(argv[1]);
    readMatrix(stream, "matrix_a");
    readMatrix(stream, "matrix_b");
    readMatrix(stream, "matrix_c");
    readMatrix(stream, "matrix_d");

}

testfile.txt

matrix_a
2 3
0 1 2 3 4 5
matrix_b
4 2
0 1 2 3 4 5 6 7 8